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How might one make value judgments regarding bidding systems?
In the comments section of this question, it was noted that the late Barry Crane would open "an 11 high card point hand containing a king. With good distributional hands open lighter." The downside to this, as a commenter noted, was that  "he built an entire system around the concept of early entry and early exit, and deliberately sacrificed slam accuracy as the trade off."
I would be wary about "sacrificing slam accuracy as the trade off" in rubber bridge or even IMPS, because of the potential for large losses of points. But at matchpoints, I am less concerned about lost slam scores and more concerned about winning 10 point "knife fights" (sacrificing 100 points to save a 110 part score).
Would such considerations lead me to choose bidding systems that make these, or similar, trade-offs at duplicate but not at other forms of bridge?


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How should I have dealt with the Capelleti interference to my partner's 1NT bid
With no one vulnerable, partner opened 1NT (15-17) after three passes. The intervening opponent bid 2 clubs (Capelletti, a system I don't understand), except that it could indicate length in any suit.. I bid 2NT with ♠ 843 ♡Q4 ♢AK532 ♣ T32. Partner passed, and we went down one, a result I considered acceptable under the circumstances (we got an average minus score). I had predicated my 2NT bid on the fact that I had "half stoppers"* in every suit, and expected the same from partner's 1NT.
Was this an appropriate response despite the down one? The other response I considered was two diamonds, which would have interfered with their "relay." The problem is that partner and I didn't know about Capelletti, and we weren't sure about whether (transfer) systems were "on" or "off."
How should I have dealt with this bid?
*A "half stopper" is a holding in NT that will create a stopper if matched with equal or better in partner's hand. For instance, xxx is a half stopper, because if partner has xxx, the opponents will have seven cards in the suit, divided 4-3 62% of the time. My Qx of hearts would be a half stopper opposite Kx or Jxx.

You and your partners should adopt the following agreement:
After a 1 notrump opening and interference in the direct seat of 2 clubs:

Double is your normal Stayman 2 club call; and
Everything else is on just as without the interference.

If the best interference the opponents can muster is 2 clubs showing an unspecified suit(s): ignore their call. Forget seeking penalties until they give you more information.
So on this hand your normal response is 2 notrump - which you bid. Getting an average minus probably means you lost a trick in the play, either from strong defense or a Declarer error, along with about half the field. As you don't give the full deal and play, it's hard to say more.

Partner had ♠ AQJT ♡75 ♢QT6 ♣ AK95. (I was hoping for as little as Jxx of hearts but didn't get it.) The heart bidder ran 6 hearts and we took the rest for down one. The two E-W pairs (out of three) that outscored us 1) bid one spade (made two) and 2) set four hearts. This group is probably not up to your standards.

@TomAu: That's just a rub of the green. Cards lay unfortunately for you, and opponents didn't make an error. Determining that your chances on this hand are better in 4 diamonds than 2 notrump, in the absence of knowing opponent's suit, seems remote.

So it was a case of "you pay your money, you take your chances," right? On a better day,  two "half stoppers" would make a whole one, and we would take seven additional running tricks. Partner did well to pass.

You don't worry about stoppers at all in this situation. When opponents overcall partner's 1NT with 2C (showing a single-suited hand with an unknown suit), you take your normal action, except that you replace 2C (Stayman) with double (also Stayman).

As @ForgetIwaseverhere says, whenever opponents overcall partner's 1NT with 2C (regardless of its meaning) your bids should mean what they normally mean, with X standing in for 2C. You should take the meaning of opponent's bid into account when deciding what call to make (e.g. if it shows majors you probably shouldn't invite NT with xx xx KJxxx KQxx). However, when it's Capelletti 2C (showing a single unknown suit), there's no real effect on the action you should take, just as it is no longer considered optimal to require a stopper in every suit to open 1NT. Don't let them cheaply derail you.

@ruds: When bidding NT, I don't require stoppers in every suit. But I do try to have "half stoppers." My bid of 2NT reflected this fact. That is, my Qx, a "half stopper" would have combined with  a hypothetical Jxx in partner's hand  to form a full stopper.

What this answer and my comment are telling you is that you should just ignore stoppers in suits that haven't been explicitly bid by opponents when you're making quantitative balanced bids, like opening 1NT, inviting with 2NT over 1NT, etc.

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Under what circumstances might some modern experts bid no trump with "offshape" hands?
This question arises from the modern practice of sometimes bidding say, 1 NT with only a singleton ace (or even king).
I would never do this with a singleton king, but might do with a singleton ace. I'm using a model that says that a singleton ace has about as much "stopper" value as xxx, with a Kx being worth a bit more, and Qx worth just a bit less. I would be reluctant to bid 1NT with xx in my weakest suit, at least unless I had compensation elsewhere in the hand.
I also don't mind bidding 1NT with a 5-4-2-2 shape if the two doubletons are reasonably well guarded, say, Kx and Ax. I would refrain from doing so if the doubletons were weaker, say Kx and xx, or conversely if they were too strong, say AK and AQ, leaving too few values for my longer suits.
Among the expert or near-expert practitioners of such offshape no trump bidding, what guidelines do they use?

Actually, singleton K's are better for 1N openings than singleton A's.  That's not because the singleton K is good at NT - rather it's because the singleton K is worthless in a suit contract but, in a NT contract, defenders sometimes underlead or duck an A.  The singleton A, however, is worth about the same at either.

Let me emphasize something.  You should never be asking yourself the question "Is this a good or bad bid?"  Instead you should ask yourself "Is this bid better or worse than the alternatives?"  (Similarly, you should never ask "Will this contract make?"  Rather you ask "Will being in this contract probabilistically score better than the alternative contract(s) (including the ones played by your opponents)?")

@AlexanderWoo Actually the singleton A is worth more in suit contracts because after you took the single trick you may be able to ruff in that suit.

I am an intermediate, but even I consider Qx doubletons to be a good excuse to bid NT at the earliest opportunity. A non-typical cases is partner having Axx (or even Kxx) opposite. If this is the opponents strongest and longest suit, you want the opening lead to come to the inadequately guarded queen rather than through it. This is often the crucial difference of having a suit doubly stopped, giving your side that much extra leeway in playing the ever favorite 3NT.

Many experts now open 1N on almost all hands that are 5422 with 5 in a minor, 6322 with 6 in a minor, or 5332 with 5 in any suit, and also "in range".  The primary reason is that, even playing fairly sophisticated 2/1 methods, these hands can be quite difficult to bid otherwise.
Suppose you hold xx AKJx xx AKxxx.  You could open 1C, but then if partner responds 1S, what do you do?  You aren't strong enough to bid 2H, rebidding 1N is a severe underbid, and 2C tends to show 6 clubs and a weaker hand.
Many experts might open 1C on AKJx xx xx AKxxx, but probably not on AQxx Kx xx AQxxx.  It's easier to get to 2H on the 5-2 fit when you open 1N; when the bidding goes 1C-1H-1S, responder cannot really rebid 2H on 5 hearts and a weak hand since opener frequently has only 1 heart.
Also suppose you hold Qx Kx KQxxxx AQx.  If you open 1D, you are a bit strong for 2D but your suit isn't good enough for 3D.  However, xx xx AKQxxx AKx is usually considered too strong for 1N.  (In contrast, many would open xx xx AKxxxx AKx or even xx xx AQxxxx AKx with a 15-17 1N.)

Great coverage of the question. To address a specific aspect of the question: Am I recalling correctly that experts now look at total flaws, rather than detailed analysis or comparison of specific flaws, when considering the possibility of opening or rebidding in notrump? That seemed to be true when I was last playing regularly at this level.

@ForgetIwaseverhere: I'm no expert, but I have a proprietary measure of suit strength: Two points for each spot card with "Work" points added for each face card. So xxx is six points. A singleton A is six points,, Qx is six points, Kx is seven. So when bidding NT I want a minimum of six suit points in each suit. Also, xxx is a "half stopper." Facing its equivalent of xxx in partner's hand, opponents will have only  a 4-3 suit 62% of the time. Qx  is a Half stopper. Opposite Kx or Jxx, the suit is stopped.

Kx and Ax. are my "optimal" doubletons. I would bid 1NT (reluctantly with Kx and Qx. I would probably do so up to  AJ and AQ (but I would want 17). Beyond that, I consider the two short suits too "top heavy."

@ForgetIwaseverhere: I think it's better to consider how flawed the hand is for a 1 of a minor opening rather than consider how flawed the hand is for 1N.  We open these hands 1N not because they are good for 1N but rather because opening 1 of a minor can cause so many problems.  I'm the wrong person to ask because I'm not an expert and my most serious bridge has been with a weak NT, where the rebid problems (especially with 5422 hands) are even bigger.

@TomAu: Meckstroth and Rodwell are well known for having won many national and world championships by bidding lots of 30% games.  Between the times when it makes on a lucky lie of the cards and the times it makes on a misdefence, they come out ahead.  Of course it helps that they are good deceptive declarers who make defenders think a lot, and, at the end of a session, they get a few extra gifts because their opponents are worn out from having to make so many difficult and important defensive decisions.

@AlexanderWoo: Yes, I like that. Opening flawed hands in notrump when it reduces rebidding complexities is the correct approach.

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Did my partner make a plausible sequence of bids?
At matchpoints, with no one vulnerable, there were two passes before North opened one club. Partner (East) doubled. South bid one heart, and I (West) passed, since I was "off the hook.
North rebid two clubs. Partner doubled that. I thought, "she must be really short in clubs, and probably in hearts. Therefore loaded in the "pointed" suits. I bid two diamonds with Q986 of the suit, with no other high card points in a 3-3-4-3 distribution. Partner bid two spades, we went down one, and got an average score.
Partner said, the second double was for penalty and that her first double showed strength in the majors. I have trouble seeing that.
I've seen a sequence of one club, pass, one heart, pass,, two clubs, double for penalty. The doubler passed and did NOT declare club shortness on the first bid.
But here, partner declared shortness by doubling the one club bid, and then based her double of the two club bid on "strength." Is there a plausible holding that can support both calls, say AK of clubs? (She actually had AT72 of clubs).

Your partner is simply wrong: all over the world, in whatever bidding system, their second double would be interpreted as take-out by good players. It's usually not that clear-cut, but this is! (By the way, what did she have?)

Your 3rd round call of 2D is correct; and you got the par result on the hand. Your analyses of the actual auction and its comparison auction are sound. Partner has no means of undoing her initial statement of short clubs, and I would read her hand as being something like 4441 or 4342 after the second double. Following Partner's two  spade call you correctly passed.
There's not much more to add.

Assuming that the 1C opening was natural, partner's first double showed (let's say) 12+ with 0-2 clubs or 18+ any shape. Their second double showed 15+ with 0-2 clubs or 18+ any shape. Your 2D call was correct; I think the 2S call must show something like 15-18 with something like a good 5-card spade suit. With a better hand for spades, partner could have bid some number of spades on her own.

A rule of thumb I learned many years ago is "The first two doubles are takeout, the third is penalty." There are exceptions, but your auction is not one of them.
So partner's second double is takeout, and should show a stronger hand than the first one did. The logic is that you had an opportunity to show moderate values by bidding after the first double, and you chose not to, so you must be very weak. Yet they're forcing you to bid anyway, and at a higher level, so they must have extra compensating values.
Doubling and then bidding a suit yourself shows a very strong hand (typically 17+ HCP) and at least a 5-card suit (6+ if they double and jump); this also negates the original implication that they're short in opener's suit and have support for the other suits. But if that's what your partner had, they should have bid their suit instead of the second double.
So it doesn't really make sense for them to double twice and then bid a suit.

I learned only the first is a takeout and the second is a penalty but I learned from a very old book.

@Joshua True, over the years double has become more and more artificial. I think the Karen Walker column in recent Bulletins has been exploring various kinds of doubles.


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Is this small slam biddable and if so, how?
With only them vulnerable, right hand opponent dealt and opened two spades (weak).
I overcalled three hearts with the following: ♠ K8 ♡ AKQJ52 ♢J976 ♣ J. I thought of making a "big" double before overcalling, but considered my hand too weak.
Partner raised to four hearts. All the pairs with our cards (including us) made six, and all but us and another pair bid six, so we shared a bottom with the other pair. The salient reasons were:

Partner had AQTxx of diamonds (giving us a double fit), and the K of diamonds was onside the finesses.
The ace of spades was onside the finesse to the K8.
Partner had the ace of clubs opposite my singleton.

How could this slam have been bid? Should it have been? For instance, could one have reasonably inferred from the opening bid that both finesses would have worked?
Or is it the case that we would have gotten a shared top if one of the finesses had failed and we did well to refrain from bidding slam despite the "poor" result?

Please give your partner's hand. It's hard to give a full auction with only bits and bobs of information.

@ruds: Partner's hand was ♠ Q ♡ 9763 ♢AQT53 ♣ AQ7.

This is a very deep question; and it's not at all clear to me that you should be bidding this slam - it depends critically on what you know about opponents (ie are they top 1/4, second 1/4, or bottom 1/2 of the club) and on their exact agreements ( in 1st seat red on white) on opening Weak Two's, opening major suit Preempts at the 3 level, and opening major suit openings. Please expand without telling me any more about their actual holdings, and specifically without telling me the location of either spade jack or club king, or a possible seventh spade in opener's hand..

@ForgetIwaseverhere: Our opponents were among the most solid and conservative players in the club (although I don't know their conventions).. It is divided into two groups, call them A and B. I typically score in the 45%-50% range against this, the "A" group, (49% on this occasion) almost 60% against the "B" group, and in the 50%-55% range in a "blended" crowd. More than the specific advice, I am glad to hear from you that this is a "deep" non-trivial question. My guess is that on amost days, one finesse fails and we share a top.

@ForgetIwaseverhere: This slam may be biddable against particular opponents in the club who would routinely overcall with AQxxxx or Ajxxxx of spades (spade finesse works), and little else (diamond finesse works). Our opponents weren't among these people although on this day, both finesses were "on."

I agree with you; you don't have the right hand to double and then bid hearts. I would not choose that course of action over a one-level bid, much less over a preempt.
In my opinion, partner is too strong to raise directly to 4H. A full opening hand, known fit with 9+ hearts, two aces, and shortness in opponents' suit should have partner thinking that slam is possible, even though you are somewhat limited by your bid of 3H instead of doubling. My choice with partner's hand would be a cue bid of 3S.
A reasonable (though somewhat aggressive) auction could be something like
(2S) 3H  3S
     4C  4NT
     5H  6H

3S shows a good raise of hearts. Overcaller is pleased to hear it and cooperates with 4C, a cue bid showing first or second round control. Now advancer sees that all the suits are controlled and partner is slam positive, so makes a somewhat aggressive move and asks for keycards. When partner shows two with the queen, we're off a keycard so we settle for the small slam.
You were fortunate to have so little interference from opponents. With a 10-card fit in spades, opponents should have been more in your face. I might expect some tables to start (2S) 3H (4S) 5H (P). Now you're in a tough spot but probably have to try 6H.

This slam may be biddable against particular opponents in the club who would routinely overcall with AQxxxx or AJxxxx of spades (spade finesse works), and little else (diamond finesse works). Our opponents weren't among these people although on this day, both finesses were "on." Responder would have to bid four diamonds, and the overcaller would have to make the aforementioned inferences (or hope the responder had at least the AK of diamonds).
This seems to be one of those plays that often work against a weak field, but probably should be shunned by players of serious bridge because they will usually fail against sound players. My guess is that on more days than not, one finesse fails (most likely the diamond finesse) and the two cautious pairs share a top. And even in this field, our opponents were among the sounder ones.

Tom, There is no spade finesse on the pair of hands you gave. Q across from K8 means that you will always lose exactly one spade trick no matter which hand holds the SA, and that this will establish for your side a trick in spades.

The following hands are all reasonable 2S openings in first seat unfavorable:

AJTxxx x xxx KTx
AJTxxx xxx x xxx
AJTxxx xx Kxx xx
AJTxxx xx xx Kxx

This hand is not a reasonable 2S opening first seat unfavorable: JTxxxx x Kxx Kxx (too much defense, trumps too poor). I rate it at slightly better than 50% that the diamond K is onside.

The bidding is already well explained in ruds answer but they didn't address the finesse. First, opponent opened a weak 2 spades in first position. You have the K of spades. So if the opponent doesn't have the ace they have neither of the top two honours. You can ask your opponents about their exact requirements for a weak two opening in first position but 6 spades without the top two honours seems too weak in first position (it's probably fine in third position after 2 passes).
Next a good weak two opening hand has little values outside the trump suit which makes it more likely that the king of diamonds is to your left.
I don't think you can guarantee whether the finesses will work but the odds here are much better than the 1 in 4 you have with no extra information.


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Which of the following hands are good enough for a takeout double?
With only them vulnerable at matchpoints, the dealer opens one club.
I would make a takeout double in the second seat with the following: ♠ AK97 ♡ K763 ♢6532 ♣ 9. It's only 10 high card points, but I have a nice 4-4-4-1 shape.
My partner in the second seat actually had ♠ AK97 ♡ K76 ♢6532 ♣ 93. Same 10 high card points but the shape is not quite as good. She passed instead of doubling.
Would most experts double or pass with my partner's cards? And would any significant proportion of experts pass instead of doubling with the first (4-4-4-1) version of the hand?

Here's a really simple rule:
Never pass a hand that Goren would have recommended acting with.
Modern bidding is more aggressive than the style Goren recommended, which results in calls being found for hands which Goren would recommend passing with. But never the other way around.
Applying this to your question:

Double with ♠ AK97 ♡ K763 ♢6532 ♣ 9; and
Pass with ♠ AK97 ♡ K76 ♢6532 ♣ 93.

The first Goren evaluates at a nice 12 Points, with 2 1/2 controls, while the second is merely 11.


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How should an intervening bid have changed my response?
With only us vulnerable at matchpoints, partner (South) dealt and bid one diamond. If West had passed, I would have bid one spade (one over one) with ♠ JT83 ♡ Q943 ♢J87 ♣ Q2. For this, I have minimum values.
But West overcalled with one heart. I (North) still bid one spade, which partner took, perhaps reasonably, for my having five spades. (See last paragraph.)
An alternative bid to show four spades might be a negative double. But my understanding is that this bid means "I don't like your suit and I don't want to defend the opponents' suit; i.e. I would prefer to play in one of the black suits, not red." But that's not the case, because I don't mind defending hearts or being dummy in diamonds.  Also, I'm not sure that that my six high card points are adequate for a negative double, so I don't like this bid.
Should I have made a negative double despite my misgivings? Or was there a better call, perhaps "pass," since I don't mind defending a heart contract?
East bid two hearts, partner raised to two spades, West bid three hearts, and partner competed to three spades with minimum value: ♠ Q52 ♡ T ♢AQT94 ♣ AT93. We went down two and got a bottom. We would have gotten an average score by letting the opponents play three hearts, and a top score if our opponents had been kind enough to let us play in two spades (down one). Did my one spade bid wrongly encourage partner to go to three spades?

Just make a Negative Double. If partner bids 2 clubs preference back to 2 diamonds, as Partner is at least 4-4 in those suits. If Partner bids 1 spade, 2 diamonds, or 1 no trump just pass. This is easily the most descriptive call available, and poses no likely downstream problems. The 1 spade should always show something better than a negative double, be it a fifth spade or an extra queen.

@ForgetIwaseverhere: So a negative double is weaker, not stronger than a one over one bid. I had not realized this. And if my hand had been just a bit weaker would "pass" have been the appropriate call?

Correct - hence, I suspect, why the name Negative Double is more popular than the original Sputnik Double.

Sorry, you're right -- I was mistaken. I meant I've never seen an agreement that bidding 1 spade here included hands with only four spades.

@ruds: Good. That's what I figured you meant. I flagged your first comment above as no longer needed, and deleted my comment directly above.

If you take an action with this hand, double is the correct action. Pass is also acceptable, but I think it would be a very conservative approach and would expect most of the field to act. In this circumstance, the Negative Double is treated by most North American pairs as showing exactly 4 spades and 6 or more points, while a bid of one spade promises 5+ spades and 6 or more points.
Note that the negative double is not limited, contra some of the answers and comments on this question; that is an agreement that I have never seen before. However, this is a bit of a special case auction: partner opened one of a minor and opponents overcalled one heart specifically.
If partner opens 1C and RHO overcalls 1D, your negative double shows 4-4 in the majors and a bid of one of the majors shows 4+ cards in that suit and 6+ points. If partner opens 1 of a minor and RHO overcalls 1S, your 2H response shows 5+ hearts and extras (say 10+ points), so the negative double has to cover heart oriented hands that don't fit this rubric: all responses with 4 hearts, and hands with 5+ hearts and say 7-9 points.

Perhaps my comment was unclear. I didn't mean that it was limited at the top end, but rather that it reached lower than a new suit call. I've known very, very, good players who aggressively bid 1 spade in these auctions; but never with both a minimum response and just 4 spade cards.  Their thinking was that, occasionally and often enough, one got to bury opponents spade suit this way. I've never been quite that aggressive myself.  The fifth spade in addition to 6 points does of course comprise an extra value.

I see. I would still argue that this is not a standard agreement in North America, and not something I would mention in response to a question about the basics of the negative double, but I don't doubt that there are some experts who intentionally widen their 1S to pick off opponents' suit.

@ForgetIwaseverhere: I use a "grid" in making my bidding choices. Here, ideally, one would have five spades and 8+ points for a one spade call. Five spades and 6 points might work, as might four spades and 8+ points. But four spades and 6 points doesn't work because it is a double minimum or "saddle point" on the grid.

I think that's one approach. My sense is that the standard is X = 4 spades, 1S = 5 spades, regardless of strength, because degree of fit is more important than strength for making decisions in a highly competitive auction. If opponents stay out of the auction after bidding 1H, our side will have opportunities to differentiate strength for a game/partscore decision.

Understand that the issue is that your hand is very borderline for a response of any kind.
If the bidding had been one diamond, pass, to you, you had barely enough for a "one over one" bid of one spade. With West having overcalled one heart, there is no reason for you to make a "free" bid of one spade, because the overcall gave partner a chance to speak again. For a "free" bid, you should have either five spades with your six high card points, or 8-9 points with four spades, as Forget pointed out in a comment.
Your hand is, however, barely strong enough for a call, with that being "double" (negative). That hints at your four cards in the unbid major, and promises the six high card points (but no more) that you actually have. Note that the double does not raise the bidding level. With a hand any weaker, you should pass.

Bidding 1S in this situation with 4 spades and any number of points is not a standard agreement in North America.


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Is it more important for a responder to bid their suit or raise partner under the following circumstances?
With only us vulnerable at matchpoints, I oponed one heart after dealer passed. The second opponent passed and partner had the following for a response: ♠ AQJ74 ♡ 742 ♢K754 ♣ 7.
I would have expected a one spade bid (one over one) from him but he felt that it was more important to show his heart support.
More to the point, he raised to three hearts (invitational).I raised to game and we went down one, because I believed that he had more strength than he actually had. Specifically, I would have expected either a fourth trump with ten high card points, or at least twelve high card points with only three trumps. And his "three" was pretty nominal. (So, in all fairness, was my five, with A8653; we each had minimum trump strength.)
Was partner right to bid hearts instead of spades? And if hearts, was two hearts or three hearts the better bid?

Despite partner holding only 10 points, I feel that his hand is closer to a game force than to a 2H call. The hand has a good 5-card side suit, ruffing values, and good controls.
The 3H call is not completely wrong when playing Standard American. The SAYC booklet says that a 1S response tends to deny a heart fit, and that 3H shows 10-11 dummy points with three or more hearts. As you have noted, three vs four trumps can make an important difference in how well your two hands mesh, which is why many pairs establish agreements that allow responder to differentiate, but no such agreement exists in basic Standard American.
However, I agree with Joe's answer that 1S is a better call than 3H. If you were to rebid 2D, 2H (promising 6), or 2S, I would bid a game (4H over 2D or 2H, 4C over 2S (splinter showing short clubs; a mild slam try in case partner has no club wastage)); over your 1NT or 2C rebid I would invite with 3H.

The stronger your hand is, the slower you want to go in most cases, with the exception of specific highly descriptive bids. Each higher bid you make eats up space to find the exact right contract - and a partnership with 23+ points needs that time to find out whether they are in a low-point-game, a high-point-not-game, a normal game but in a different suit... all the other possibilities than the standard 'okay we have a heart fit and borderline game points'.
As such, 1h-3h is definitely not what this hand asks for.  10 points is plenty to have a conversation at the lower levels first.  1H-3H is realistically only used to describe invitational hands with clear heart fits - as you say, usually 4 hearts.  (Many use Bergen raises anyway for this, but if you're not using them, that's what it should mean.) 10-12 points, 4 hearts, nothing else interesting to talk about.
Whenever you do have something else, you want to show it as soon as possible.  If partner also has 3-4 spades, for example, you don't want to miss that - you might still end up in 4H, say, but the double fit is useful to know as it implies additional tricks (but also requires full control of trump to make use of).
Think about what you're going to bid here:

S
N

1H
1S

2C
?

Do you rebid spades? Do you bid 2H? Do you bid 3H? (2D would be fourth suit forcing, probably not in the cards here.)
You need to know what 2H vs 3H raise means here, in particular.  2H might be minimum, 4S/3H fit.  3H might be invitational here and just wanted to mention spades first.  I'd make sure you agree on what count of trump 3H bid would show here (I think 4 is still often a good idea here).

I agree with everything until your last paragraph. How is AQxxx xx xxx xxx or AQxxx xx xxxx xx supposed to bid after 1H-1S; 2C except to bid 2H? 2H has to be available as a preference bid, so 3H can't really promise 4 trumps.

Yeah, rereading that I think you're right that 1s->2h has to have that space... removing that last line.  The point of the paragraph is to figure out what exactly you do in those hands though - 10p 3h needs to have a space it's slotted into.

As responder, I would bid one spade, and re-bid only two hearts, since my "three" hearts are so weak.

meh, 2h here is pretty weak as your second bid, you have values that suggest game is at least possible; you should explore a little.  2h is okay only if you really have no other option.  1h-1s-1nt-2h shows a much worse hand (it could be as little as KQxx-xx-Qxx-xxxx).  You've got something like 2.5 more tricks than that hand does!  That said, though, if you would open 1nt with 15 points and 3-5-3-2, then the 2h might be okay (since partner is capped at 14).  3h jump is perhaps permissible there - 1h-1s-1nt-3h - showing the heart fit and near game values.

2d is another possibility, but honestly the 3h jump might be best if you agree it is invitational showing 5-3 or a good 4-3.  Partner then passes with their 12 count and 5 mediocre hearts, and you're in the exactly right contract.

You don't say what bidding system you play. If you are playing Acol, then partner's bid definitely shows four card support and 10-12 high card points. In SAYC, at least according to Ned Downey, a jump to three of partner's major is invitational, with 10-12 points and at least three card support. Your partner has only seven losers (i.e. an opening hand), a strong side suit and a club singleton. In my book definitely worth an invitation.
You don't give your hand, nor why you raised to game. If you had the king of spades, then you are looking at 8½ tricks on the cards we know about and were unfortunate with your remaining high cards. Possibly you were missing the aces of clubs and diamonds, to go with your two heart losers; possibly you had wasted values in clubs; in the worst case the diamond ace and queen were sitting over your partner's king and you lose two or three tricks on the opening lead.
If you didn't have the spade king, you certainly had 10-11 points outside the majors; if you don't have first-round control of clubs you certainly have the ace of diamonds. That would make it a 50% game (spade finesse), and you should bid 50% games. Counting losers, you have at most seven for an opening bid, partner has seven, so contracting for 10 tricks would the par recommendation (24 minus your seven losers minus partner's seven gives 10 tricks).
If you don't want partner to raise to three of a major with seven losers and three card support, discuss the hand with them - would you prefer to show the spade suit, do you want to widen the range for the 2H, and how do you cope with the resultant ambiguities in those auctions? It's a partnership, both of you should have input into your bidding system.

The rule is ‘showing support for partner’s Major always takes priority over showing your own suit’ - However showing support doesn't necessarily mean bidding partners suit!! What isn’t explained well here, is there's no one correct bid to apply. There are different sets of rules which disagree on whether you ought to bid hearts or bid spades first in showing support. (Although having found one major fit in hearts, you aren't bidding spades to find another fit). The 'correct' bid depends on several 'variables':

The system you are playing: Even 2/1 and SAYC apply different rules (let alone Acol!)
Whether you adopt any Conventions (like Bergen, fit-jumps, etc)
The length and strength of the suit(s).

Too many permutations to cover, although mostly they just differ by which fits are denied by a 1S bid, and whether the jump-raise in H promises 3 or 4 cards. Ignoring Bergen (and many others!) I believe it's common that:
In SAYC, responder raises with 3 hearts, (2H weak and 3H invitational) so 1S typically denies 3 hearts
In 2/1, responder wants 3 hearts for a minimum raise and 4 hearts for an invitational jump raise; So 3H might be misleading here and 1S followed by a 3H jump-raise is clearer.
EXCEPT! This responder's hand appears to have only 7 losers! so responder could insist on game themself, and stopping at 3H could be under bidding the hand!
Jacoby 2NT and Splinters generally need 4 card support; However I think 1S is generally a good and flexible course of action in most systems, hoping to show support with a 4H delayed-game-raise. But, when opener inevitably replies 2C! responder must either conservatively recognise wasted points in Clubs and Spades and settle for 3H - or see a cross-ruffing opportunity and optimistically plump for 4H.  (Would you raise their 3H to 4H regardless with the undisclosed hand?) Checkback could be useful over a 1NT reply (although to investigate how well your hands match rather than looking for spade contract).
Generally in all systems, showing (major) support is always the first priority, however showing strength is an even Higher priority! - Thus, sometimes a delayed raise is the best description of support (it's not about any other suit, its whether the correct Strength and Trump Length are described under the partnership agreement).
Addendum: You want a suit quality of at least 10, in order to impose your own major suit on partner, so AKQJxx or AKQxxxxx (or better).


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What is meant in matchpoints by "opponents have control of the bidding and play?"
This possibility was raised by "Forget," in answer to this question, and comments about it.
Could it be a phenomenon I've noted under a different description: My partner and I earn a (theoretical) par score but we get a bottom or near-bottom because we had tough opponents that held us to the par score while other pairs with our cards got better scores than us because their opponents weren't as hard on them?
Are the two things the same? If not, how does paragraph 1 differ from paragraph 2? And in event, what causes this (or both of these) situations?
Sometimes these situations happen in your favor. Is part of the "luck" of matchpoints how many times they favor you, as opposed to your "table opponents" (people playing at the same table, e.g E/W versus your N?S, not other N/S pairs)?

Yes, this is part of the "luck" of bridge. Some hands are not difficult at all to defend, e.g. one opponent has the AKQ of trumps, and there is no other chance of a trick anywhere. The opponents will take three tricks regardless how good they are. If you play such a hand against players better than you then you got lucky, because they couldn't capitalise on their skill.
Conversely, if a hand is difficult to defend but the defenders do so successfully then your score will generally be below average. This is sometimes referred to as "declarer's advantage".

Yes, this is part of the "luck" of bridge.  And JDL is correct that some hands that "play themselves" mean that if you get them against the best pair in the room, you're likely getting out of that round with a better score than the field, where their skill gets a chance.
But the quote: "the opponents have control of the bidding/play" usually implies almost the opposite of that case: a hand where we have no meaningful decisions, but they do.  Examples:

we have 7-8 HCP and no suits.  Now, it's up to the opponents:

if slam is on, and they find it, you're getting a bad score.
if slam is obvious, but your opponents find 6NT and it's right, you're getting a bad score.
if they stop in 3NT, and it turns out that 12 tricks just aren't there despite the fit and the 33 high, you're getting a bad score (and they're rewarded for their bad bidding!)

Similarly, the opponents are the only ones in the room playing Precision, so they're the only ones that could find the jack needed to bid the grand that everybody makes (Note: I have one in my history where "because we were the only ones playing Goren"; my 1♥ on 4 and 15 HCP got us there where after the room's 1NT they couldn't resolve it).
The auction is going 1NT-3NT across the room.  Now, your defence may matter, but sometimes it doesn't; the only thing that matters is whether declarer can play to make -600, -630 or -660.
the only relevant decision on this hand is a two-way guess for the Queen of trumps.  If they get it right, they get a good score; if not, you do, almost independent of your skill.  Doubly so if that's the setting trick.

So, almost always this phrase is used in cases where the opponents have a large majority of the points and you are likely to be passing throughout; or where your defence (unless it's unusually poor) isn't really going to matter.
An example where "large majority of HCP" doesn't apply: "this pair is the only one in the room playing a weak NT".  Now, any time they have a balanced 12-17 and get to open, the auction is going to be different.

Many times that isn't going to matter;
Sometimes it's a weak NT opener passed out, where a 1m opener would let the opponents in;
Sometimes it's a weak NT opener passed out where the field is finding their 4-4 major fit;
Sometimes it's just that the normal contract is played from the other direction and the other hand is on lead (and top or bottom depends on which defender has the "killing lead" in their hand).

Again, on the hands where this is relevant, your good or bad score is almost entirely dependent on whether the hand is good for the weak NT system or for the strong NT field.
As to your last paragraph: note that, due to the single-dummy nature of bridge versus the double-dummy nature of "par", there will always be hands where par is an incredibly poor score for one side or the other.  Sometimes, "being held to par" for a bad score is declarer's poor play rather than the opponents' brilliance.  There are even hands where "playing the par defence" is more likely to get you a trip to ethics than commendation for your brilliance.
When you get a "we made par, but it's a poor score" it is always worth it to analyse the hand and see what the reason is - it's usually not "the field played badly"; frequently also not "the opponents defended better".  Frankly, when comparing to par, it's always worth a quick analysis to see if par is anywhere close to "what would happen at the table".


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Should I have raised partner or bid 1NT in the following situation?
Both vulnerable at matchpoints, I dealt and opened one diamond with the following:
♠ A86 ♡ K86 ♢QT75 ♣ KT5.
Partner bid one heart. I was taught to raise a "one over one" bid to two on my second bid as opener with Qxx or better and a minimum opening hand.
After partner bid and made four hearts, she said, "Yes, I had five hearts but I might have had four. I wish you had bid 1NT with only three card support."
I replied that my solid three card support was the most salient feature of the hand, and I needed to convey that information because I might not get another chance to bid.
An opponent weighed in with the following: "In your shoes, I would have bid 1NT because of the the 3-3-4-3 distribution, but I would have raised to two hearts with a ruffing value" [doubleton].
Who was more nearly correct? Partner, the opponent or myself?

Modern practice (which assumes that at least Check-Back Stayman (CBS) or New Minor Forcing (NMF), if not XYZ, is being played) requires that all balanced minimums be rebid at the one level (whether with 1NT or one of a 4 card major suit) when available. The sole exception is when holding 4-card support for Partner's major suit.
The reasons for this are myriad, but boil down to the combination of better bidding systems allowing more precise distinction of hands when one's system works this way - and that's, very simply, just much better bridge.
If your system doesn't incorporate this approach, including whichever of CBS, NMF, or XYZ your partnership has chosen, then adopt and adapt. You are handicapping yourself measurably, as these hands are quite frequent. All of these sequences now clearly signal that Responder, if with the unlimited hand, is captain on the auction; and the immediate single raise of Responder's major suit shows four card support, with options later to show just three card support.
Finally - this is not new. This practice was filtering down from the experts into high intermediate level more than forty years ago. It has always been a core pillar of Five Card Majors as promulgated by Max Hardy since at least the 1974 edition of his eponymous book.
Some history:

Although they played a Weak rather than Strong opening 1 No Trump, Kaplan-Sheinwold in their 1962 book How to Play Winning Bridge, outlining their early East Coast experiment with a Five Card Major system, employ the same structure:

The opener would raise hearts if he had four-card support for that suit. He would show a new suit at the level of one if he could.

At the same time, Goren's 1964 edition of New Bridge Complete states (playing four-card majors of course):

Rebid by opener after take-out to 1 of a suit

If your opening bid was approximately minimum strength, this the time to make that announcement. The message is conveyed to partner either by a rebid of 1 No Trump or a rebid of 2 of your suit, which ever best describes your hand. ...

*The naming of a second suit at the level of 1 requires no additional strength. ...

The naming of a biddable four-card major suit at the level of 1 takes precedence over rebidding even a good six-card minor.

Raising partner's one-over-one response to 2

... Wherever your hand contains four of partner's trumps, or where it contains a singleton and normal support [Footnote: At least three trumps, usually with a high honor] for partner, you may raise once even with a minimum hand.

To find even the barest support for your chosen call, I had to go back to Culbertson's 1936 New Gold Book of Bridge. Culbertson's system precedes the development of various modern arrangements, so is less hasty in responding 1 No Trump. However, his requirement for a single raise in Responder's suit is:

... and the opener has adequate trump support for the responder's suit, he may count his winners exactly as though he were the responder's hand ... and the opener should raise once if he has five supporting winners.

I fail to see how your actual hand can claim "five supporting winners" in support of Hearts. My count is a bold stretch to even get to 3 1/2. Yes, Culbertson played a more aggressive game than he preached in his books - that's still not eliciting a 2 Heart call on this rat-bag.

If "The naming of a biddable four-card major suit at the level of 1 takes precedence over rebidding even a good six-card minor." you might want to take a look at this question and the two answers. The minor suit advocate was upvoted, and the major suit advocate was downvoted. (I didn't contribute to ither vote total because I didn't feel that I knew enough to vote.) Note, however, that I was the responder (not opener) and bidding for the first time with a four card major and six card minor.

US expert standard has mostly moved on to XYZ, which uses both 2C and 2D as artificial bids to look for a 5-3 fit.

@TomAu: I deleted my earlier response. Yes, Opener rebids a four card major below the level of 1NT, if available, in preference to bidding 1 NT; otherwise the suit can get lost.  Did you intend to include a link in your comment? It seems incomplete without one.

@AlexanderWoo: Thank you. That's a great approach; and helped clarify my thinking even on auctions where it's not agreed. However it seems to me that it works even better with a weak NT opening. Is that the case? Or am I imagining things?

@ForgetIwaseverhere: The relevant question is whether you want to be able to play in 2C if opener opened 1C.  I think the answer is 'no' if opener has 15-17 balanced and 'yes' if opener has a minimum unbalanced opener.  (I prefer to play that 1m-1H-1S promises an unbalanced hand, especially playing weak NT.)

@AlexanderWoo: I'd agree. Distinguishing NT as a desired, rather than fallback, denomination is too important on a weak opening to let get lost.


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What are the implications of fourth suit forcing in the following "strange" hand?
At matchpoints, with only our opponents vulnerable, my partner opened one diamond in fourth seat with the following: ♠ KQJ2 ♡ T7 ♢9873 ♣ KQ3.
With opponents passing all bids, I responded one heart, partner bid one spade, and I said 2 clubs (forcing). After my left hand opponent passed and then asked for the meaning of my bid. Partner, who was also the tournament director, ruled that she should have alerted the bid, and stated that the penalty was that she had to pass.
Was the bid generally alertable or only in our club? If so, was the penalty appropriate? What should she have bid without the penalty, 2NT perhaps? And should she have opened in fourth seat with only 11 high card points and 4-2-4-3 distribution? Or should she have taken the average score she would have gotten by passing?

There are a number of questions raised here, so I'll take them one by one.
First, was your 2C bid generally alertable? Yes, an artificial and forcing 2C bid is alertable according to the ACBL Alert Procedures. In the section on artificial bids, it is not listed among the "Other Artificial Bids" that should not be alerted.
Second, was the penalty appropriate? No, by my reading of the Laws of Duplicate Bridge. Law 21 (Misinformation), Section B (Call Based on Misinformation from an Opponent), reads in part:

(a) Until the end of the auction period (see Law 17D) and provided that his partner has not subsequently called, a player may change a call without other rectification for his side when the Director judges that the decision to make the call could well have been influenced by information given to the player by an opponent. Failure to alert promptly where an alert is required by the Regulating Authority is deemed misinformation.

Here, LHO has passed, perhaps because of misinformation, and RHO has not yet taken a call, so LHO is entitled to change a call without other rectification. Moreover, I don't even see that any relevant unauthorized information has been transmitted to you, since partner realized their mistake before taking their next call, so I don't think that any further restriction on your bidding is necessary. Frankly, I don't think any restriction on your partner's bidding would be warranted even in other twists on this situation unless you said something before the end of the auction (or end of play, if your side ended up defending) to indicate that partner failed to alert.
By the by, LHO should have asked your partner about the meaning of your bid before taking a call. I suppose that your partner may have been thinking about her bid before being woken up to its meaning by LHO's question, but that is not unauthorized information -- that awakening was caused by your opponents, not you.
Third, what should her rebid have been after your 2C? Yes, I think 2NT is perfectly appropriate. Partner doesn't have 3-card heart support or a suit-oriented hand with rebiddable diamonds, and does have a club stopper. She clearly doesn't want to be in 3NT, but 2NT may well be the best spot.
Fourth, should she have opened in fourth seat? I think at match points this hand should be opened; the nice spade suit means that her side is not likely to "lose the auction" by allowing the opponents to back into a nice 2-level contract. As another answer indicates, 1S is a good choice for opening, but I do not go as far as he does and say that it's the only possible choice. 1D is also reasonable if she just treats this hand as a 12 count; her honor structure is nice and there are some nice spot cards. I think that choice is more defensible if your practice is to rebid 1NT with minimum balanced hands even with a four-card major, reserving 1S for more distributional hands.

Partner should have simply opened 1 spade, and passed any natural response from your hand. Partner should rebid to show Bad-Hand/Bad-Suit over Drury; and convert any other non-natural raise to the minimum number of spades.
Hands that open 1 diamond in fourth seat should have fit one of these patterns:

A hand that always opens 1D in second seat vulnerable against not. These hands should have a good chance of making 9 tricks in Diamonds or 8 in No Trump, even opposite Partner's pass. This isn't such a hand.

A hand that is 3442, below minimum strength but opening on the basis of its Pearson Points; and will pass any call by responder. This isn't that hand either.

What Partner has, instead, is a hand that opens in Fourth seat solely because of the Spade suit. These hand MUST open 1 spade in order to enable Drury, allowing Partner to show Bad-Hand/Bad-Suit, and get out in a 2 spade contract. This is that hand. The spades are opened in order to smother opponents' possible heart fit.
Instead Partner tied herself up in knots, and gave opponents an opening lead roadmap to the hand.

Would you make this bid in third position? Partner has still passed, and there might be at least the merit of shutting out fourth seat from bidding one of a suit.

@TomAu: Assuming Drury or equivalent - absolutely.

I'm not sure I would do this with four hearts instead of four spades because of the possibility of a one spade overcall that reduces my equity.


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How do good partnerships adjust their systems when overcalling, instead of opening, 1NT?
Over an opening bid of 1NT, responders will use a variety of systems, such as Stayman, (Jacoby) transfers,etc.
But suppose the sequence was South: 1 diamond, West 1NT, North, Pass, and you are East. You are confronted with the fact that you are dealing with an overcall, and South's one diamond bid means that if you bid 2 clubs (and partner responds two diamonds), or you bid two diamonds yourself, you are bidding the opponents' suit.
Do good partnerships persist with "systems on," or would they revert to natural bidding, or is it "some of each"? What are the advantages and disadvantages of "systems on" versus "systems off"?

In my experience, most partnerships simply play System On. The intent and extent of inquiry is not, for the most part, affected by the existence of a prior opening call. This makes the benefit of a modified system fairly small, particularly compared to the memory and discussion cost of an alternate system.
For more rigorous partnerships, perhaps a transfer into Opener's (major) suit may be a specialized asking bid; but I see no benefit to doing the same in a minor suit that is frequently only 3-cards long.
It's been a very long time since I played regularly against truly top-notch opponents; so as to what those top-tier experts are currently doing here I will not speculate.


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Does it make better sense to open "light" in matchpoints than in rubber?
By "light" I mean with something like 11 high card points and a five card major suit or 10 high card points and a six card major headed by at least two honors. My (limited) experience has been that I will make my contract almost as often as if I open with 12, but there will be times when my "lightness" will cause me to go down much more.
In rubber or money games, the occasional big loss will be a deterrent to any given activity. But in matchpoints, my main worry is about a "rounder" bottom. Also, if others are opening light and they go down with me, I won't look so bad on the "curve."
In my duplicate club, pairs that stretch bid tend to do better in close auctions (both pairs have about 20 points each) than pairs who underbid (by an equivalent amount). Is this, in fact, a feature of matchpoint scoring?

You're obvious has a confound big enough for Icon of the Seas to sail through: Yes, better players will regularly score better. They bid, call, and play more accurately because they evaluate hands, particularly difficult hands, better; and more accurately read the cards behind opponent calls. That naturally looks like aggressive bidding when aggression is called for; and caution otherwise, which you're ignoring. 1/2

Better players make accurate decisions more reliably, both in being aggressive when aggression is called for and in being cautious when caution is called for. Looking at only one side of the coin, and opting to be blindly more aggressive without actually improving your card reading and play, will lower your score not raise it. Simply because you've deliberately become a weaker player, by choosing to bid less accurately. 2/2

@ForgetIwaseverhere: You have not addressed the main point of the question, which is that there is a floor to the downside in matchpoints. How would this "floor" skew the bidding at the borderline?

In a word: No. Just the opposite is the case. Match Points is about consistency: the ability to sit down for 3 1/2 hours and make zero unforced errors. The reason is that there simply aren't enough tops available to overcome any avoidable bottom. Here's why.
Consider a typical club game with 12 top on a board, each pair playing 26 boards. A typical low intermediate player looking to improve is stuck scoring 156 to 168, only occasionally sneaking into the placing, is looking to add 12 to 18 points to their score so that they place regularly. Intermediates a bit better are scoring 168 to 180, regularly placing but rarely winning or even getting second, are likewise looking to improve by 12 to 18 points so that they see themselves with a shot at winning in most games.
However, there are only 26 hands being played, each one worth at most 12 points. On about half of those boards, call it 13, the scores will cluster at 4 and 8 hinging only on 1 trick in the play. Any attempt to "win" these boards in the auction will almost certainly either net a bottom for simply being in the wrong contract; or at best guaranteeing a 4 instead of an 8 by keying the opposition play. To improve your game here simply bid with the field, and improve your play so you are getting 9 or 10 scores of 8 here instead of just 5 or 6.
On another 3 or 4 boards the opponents will, whether through skill or luck, fix you. The hand was theirs to win or lose, instead of yours, and they won. Learn to accept these; and work on trying to keep these to a 3 or 4 instead of a 0 or 1.
On the remaining third of the boards, 8 or 9, both sides have interesting, and possibly difficult, decisions in both bidding and play. If you've been solid through the 17 boards above, then you clawed back enough on type 1 above to overcome your losses on type 2. You're perhaps a half board above average. To have a shot at winning you need to average 9+ on these boards, for a score of 162 + 9*2 = 189. That won't win often, but it will win on occasion; and if you're scoring this every third or fourth game, then the club's strongest players will start thinking a game with you might be an enjoyable evening.
But to get there, you need to avoid bottoms. There is no recovery from a goose-egg here; because it takes 3 tops to overcome each one. (Specifically because 9*4 = 36 = 12 * 3. This is why Top & Bottom bridge is always losing bridge - there simply aren't enough tops available to overcome a couple of bottoms.) The key is very simple: bid, play, and defend these hands near perfectly. (I.e. with no avoidable errors.) Be skillful. Forget weird bidding heuristics. Evaluate your hand well; listen to the opponents passes as well as their bids; signal consistently on defense and always see and read partner's defensive signals; and avoid all actions which risk a bottom.
If you can do all this, your game will move from the field's average of 156 up into the mid 170's. The occasional 190 or even 200+ game will come your way. Stronger players will ask for a date when you're available for a game, instead of you begging them for one.
This is the opposite of IMP play, where unforced errors in uncontested part score contracts (perhaps 1/4 to 1/3 of the deals) are quickly overcome, in bulk, by a single game swing. Here, one relaxes during the part scores so as to achieve maximum focus during game and slam hands.

You told me that Barry Crane had a style of opening light, sacrificing slam accuracy (relatively infrequently) in order to win  (frequently )dogfights for part scores. That makes more sense in matchpoints than IMPs or rubber. That's what's happening in my club.  That was the gist of my question.

@TomAu: Crane's system also played 4-card majors. Is that happening in your club also? Precision and Blue Club players also play lighter openings, because the low end of their forcing opening has dropped by about 6 points. These are systemic approaches. Your question is asking about systemic variations, a very different beast. Don't conflate the two.

In my club, de facto, maybe not de jure. I once asked a question about how the club's highest scoring player opened 1 spade with AQJx.

@TomAu: I suspect because: he was playing with the second or third best player - and knew exactly when it was systemically required to lie. I doubt he was "taking a view"; but rather was avoiding down-the-road trouble.

I have, on occasion over the years, overcalled 1S with just AQJx in the suit; because it seemed the lesser of evils rather than a "view'.

I would say those two bids were competitive, and in duplicate there is incentive to compete more keenly at lower levels, so maybe light opening is a misnomer.
'Forget...' is 100% correct in saying duplicate is about avoiding mistakes, and one follows the system precisely in 1st and 2nd seats. However, passing a suitable bid is also a mistake! 11 points with 5-4 in first seat would meet 'rule of 20' as does a 10 point 6-4 hand. An unacceptable light is 11 points balanced (unless that's the convention card you play!); Some 12 point hands shouldn't open, while in 3rd and 4th Seats one effectively adopts a different bidding system that's even lighter.
The top players get good scores from bidding marginal situations well. They recognise subtle differences and bid according to the context. It is not bidding light per se but rather bidding to the situation with well-defined exceptions to 'basic' rules, so partner can still read the hand EXACTLY, and make the marginal decision needed. An opaque 'error-range' around the normal bid is always bad.
In duplicate there's more to gain from competing at a lower level, less to lose on doubled contracts, and an incentive to sacrifice; going down -1 to prevent opponents making a contract is usually better, but this comes from precise bidding at low levels and not the light bidding.
In the long term, down -1 saving 10 points 9 times out of 10 outweighs a -50 once in 10, and getting 60% 9 times and 0% once is good bridge, while 60% 8 times and 0% twice is bad bridge! Margins are thin so one's generally conservative to avoid mistakes, and 'Light' is bad where partner may misinterpret and place the contract wrongly.
But it's not a grey area, I would conclude the principle is: If you don't know which 'Light' exception you're following then don't bid it, but when you do know, then do it! And improving is about learning which marginal condition you and your partner should or shouldn't bid.


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Should I have tried for slam in the following situation, and if so, did I do so in the right way?
With only them vulnerable at matchpoints, my (new) partner dealt and opened one club. After a pass by opponent, I bid one diamond with the following: (s) 7 (h) KQ (d) KT98543 (c) KT3.
Partner bid 2NT (balanced, 18-19). I decided to try for slam with 4NT (quantitative). Counting my 11, we had only 29 high card points between us, but with seven diamonds, I added two points each for the two long diamonds (above 5), bringing the total to 33. (A pair needs about 31 to be even money for a small slam.)
Partner took my bid for Blackwood, and bid 5 clubs, showing four aces.  I took that as a sign off bid at 5 clubs, with one major suit unguarded, and figured that with three card support, clubs would be a good place. But I now believe that I should have continued in diamonds, since I had seven, and partner at least two.
We went down at five clubs (partner had a 4-4-2-3 distribution with all four aces and the queen of spades). We would have made six diamonds or six no trump.
Was I right to try for slam with my holding? Did I do so the right way or did partner reasonably take my 4NT bid for something other than quantitative? And should I at least have "pulled" five clubs to five diamonds?

4N is quantitative if you've agreed with partner it's quantitative and Blackwood if you've agreed with partner it's Blackwood.  If you haven't discussed this with partner, discuss it.  If you're not in a situation where it can be discussed, then don't care if it goes wrong, and don't ask what it 'should' be, because there is no 'should' here.

That said, I don't know of a single decent player who plays ordinary Blackwood in any situation (maybe except 1suit-immediate4N), and I don't know a single decent partnership that doesn't have some artificial bids for responder after 1X-1Y-2N to enable both finding the right game and starting slam exploration at a lower level.

Yes, the playing strength is sufficient to investigate slam - but with a new and questionable partner you have no methods for a proper investigation. So what are your odds if you just wing it?
Partner has 2/3 of the remaining points, and your main concern is that you are missing 2 aces: The odds are (close enough for bidding decisions, though possibly not for play decisions):

(⅔)4 = 16/81 = ~20% that Partner has all four of them; and
4 * (⅔)3 * ⅓ = 32/81 = ~40% that Partner has three of them.

That adds to ~60% - and you should just bid 6 diamonds. Defenders can make an inaccurate assumption from your bidding; or even just err in their analysis. These perhaps increase your odds a bit more.
Yes, the above ignores space considerations in Partner's hand - but it's easier to place 4 points in his hand with an ace than it is with 2 or 3 other cards. That is a significant counterbalance to the space considerations; he has to have his 18-19 points somewhere, and you're already accounting for 3 of the 4 kings that are the next easiest way to place a 4 point combination in his hand.
The wild card hand - yours - will be hidden; so if you still need to pull a fast one on the defense, do it in tempo on trick 1 or 2.

A few things to say here.
First, don't assume that partner has failed to understand your bid. If you think that 4NT is quantitative, how could partner sign off in 5C? That doesn't really make sense. They have no idea what you have; 5C may be a much worse contract than 4NT. It's good to have agreements in these situations, but with a pickup partner you may not. In any case, 5C has to be a forward-going bid that's looking to pick the best slam. If partner stretched to bid 2NT with long clubs (not a good idea), they just have to swallow the bad score and pass 4NT, because at this point finding the best slam is the focus. But in any case, it is sensible to be able to respond to quantitative with a forward-going bid, and less sensible to be able to respond with a signoff.
Second, it was correct to look for slam here. I disagree that 4NT is the right approach. Why do you think that asking partner whether they have a min or a max is the right way to determine whether you have slam?
The question you need to answer is this: Do you have a diamond fit and 3 out of the 4 aces? If partner holds Axxx Axx Axxx Ax then you are making seven (partner only has 16!). If, on the other hand, partner holds AKQJ JTxx Qx AQJ then you are probably going down in a small slam (partner has 20!). It's about degree of fit, and controls. Standard agreements can't handle it. Gerber could answer part of this: if partner has 3 or 4 aces, you're probably making a small slam. Without tools to find out more, probably you should just jump to 6D. It may be right, or opponents may make the wrong lead.

Agree with all - you should try.
However, 4NT isn't the try, even if you're both on the same page that it's quantitative.
You can't add length points to your HCP to make a quantitative slam try; it needs 33 Miltons.  Because otherwise you can be off two aces.  The game doesn't care if you can take 16 of the last 11 tricks if you're off two aces that get cashed first. (yes, even with 33, you can be off AK suited.  Very very rare.)
You are correct that 31 with two balanced hands is slightly better than 50% to make slam; but only if you're not off two quicks.  The way to find that out is not "pretend I have more HCP than I have; the two aces will magically compress into one".
Without agreements, I like bash-and-hope; at least it doesn't (until dummy comes down, in 6NT - which is why 6♦ was the suggestion, and is the right bash) flag that there could be two aces missing, unless they're both in leader's hand (or that they cash! You didn't ace-ask, why?  Because you have a void!)
Definitely agreements help; in this auction, I play "the only non-game-forcing call is pass" with almost everybody (including, without discussion, pickup partners in my city).  I have an alternative to 6♦ - 3♦.  100% forcing, clearly a slam try (else why not just 3NT? or in very odd cases 5♦?), partner should be able to evaluate.  And I've pointed out the focus ("tricks are coming from running my suit") and we have the entire 3 and 4 level to work out the rest.
Others, as shown in their answers, have other methods, but mine are simple.  I understand that in your circle, you don't have that guarantee (I agree, +190 is an embarrassing score!) - but you should.
But even without those agreements, there's an evil one that might just work.  As ruds says, 4 aces and out should be golden; 4♣ is Gerber (for almost everybody), no?  (Which is why 4NT can be quantitative)

Yes, there are those who think that 4NT is blackwood (of some sort), and 4♣ is Gerber, and never clue into the fact that they have two bids for one situation and zero for another.
Yes, I would be very happy if nobody asked me to play Gerber ever again (several of my partnerships have "Gerber is baby food" on the card).
Yes, even with this hand, Gerber is wrong (what if you get 3?  Do you have a call that says "slam is on if your hand is good for diamonds" and a call that says "don't you dare go on, we're off two aces" if partner showed only two?), and there are clearly better ways to bid this (which is why I would be happy to never play it again - it's too easy a crutch for even experienced partners to jump for).

but it's still better than "go on 19, don't on 18, I don't care how many aces you have, because we won't be off two if you go."
Having said that, it is clear that 5♣ is not to play and must be "partner thought I was ace-asking".  There is just no hand that was willing to play 2NT that prefers 5-only-clubs to 4NT opposite no known support.  Your "open major"?  How does she know that you don't have it stopped?  You made a bid that said "if you have one more HCP than you have, we can make 12".  Without that point, now your hand won't cover 3 losers in that suit?  (ah, but you didn't actually do that.  And since you don't have that extra Q, just the two long diamonds, you "could see" the potential problem partner could have.  Notice, though, that partner can't see it!)
Whatever it showed, you are right you should correct to diamonds; partner will guess right.  To bring up yet more of my agreements, Meta-agreement #1: "Confusing bids are forcing" (that might apply to both partners here!)

I'm going to be obnoxious here, and pretend you're playing with my agreements with one of my partners.
First, this is definitely worth a slam invite.  The question you should ask is: Can you imagine many balanced 18 point hands opposite which slam is good?  The answer is yes - Axx xxx AQx AQxx makes 6N, and is only 16 points.  There are many variations.
Now - how do you either ask partner if they have a suitable hand or tell partner what a suitable hand would be?  The cards you're asking for are aces, the queen of diamonds, and the third diamond.  The queen of clubs is useful if partner does not have Axx(x) of hearts (or AK of spades).  The honors that are useless are the lower spade honors.
So I bid 3C, a transfer to diamonds, followed by 3S after partner's 3D bid.  The 3S bid shows slam interest and shortness in spades (telling partner that lower spade honors are useless).  If partner bids 3N, I make one more try with 4D, after which I'll pass partner's 4N or 5D bid.  If partner bids 4C (ace showing) or 4D (interest in slam), I bid 4H, which is keycard asking in diamonds.  If partner bids 4H, I bid 4S, showing one (or four, in theory) keycard.  If partner bids 5D, showing a terrible hand with no spade stopper, I pass.  If partner bids anything else, I bid 6D.
(These are hardly the most implausible agreements.  In fact, one bridge club in Seattle ran an individual a couple years ago with these as part of the imposed system.)

Here's my interpretation of my own bidding: "We've talked about clubs and diamonds, and I am promising 14 points opposite your presumed 18.. This would give us 32, making us odds on for 6NT, except that I'm worried that you have only Qxxx in one of the majors or Kxx in both,, causing us to lose the first two tricks. I only had 11 high card points, but my 7 diamonds should be worth two extra tricks (compared to five diamonds." I took five clubs to mean "I'm "open" in one of the majors, so let's play in my first-bd suit.

Slam bidding is not about counting points, but actually picturing how you will take 12 tricks.

I can count to 12 tricks with the two hands. Six diamonds, two clubs, three hearts, one spade. The only question is, can the defense win two tricks, say a diamond and the king of spades, before we get 12.

You're avoiding doing the right exercise.  1) figure out 5 different hands for partner (different in more than just low spot cards), consistent with their bidding so far, for which slam will likely make (against best defense).  2) figure out 5 different hands for partner for which slam will likely fail.  3) figure out a sequence of bids which will either give you the information to distinguish the first 5 hands from the second 5 hands, or a sequence of bids which will get a thinking partner to bid to slam on the first 5 hands and not on the second 5 hands.

Actually, I do an abbreviated version of this exercise. First, I make an inventory of outstanding honors (those not in my hand). Then I evaluate partner's bids, e.g. s/he opened and therefore has at least 12  points. Then I assign the best and worst possible configurations of partner's "12" points and see what I come up with. That's why "points" are so crucial to my analysis.

@TomAu: That's not "abbreviated", but rather "simplistic". Reason is that if you're not doing five distinct at each end you have no way to accurately estimate weighting between the two. Your method assumes that the arithmetic mean equals the median - which is frequently not the case when the distribution is uneven.


text:
Can a J-T combination be counted as a single honor under a "two honor" rule?
There are times in bridge (e.g. when opening a "weak two") when a bidder needs a strong suit headed by at least two out of the three "top" honors, that is A-K, A-Q or K-Q. The weakest of these, K-Q, has one guaranteed "top" trick.
The rule is designed to prevent bidding (under these circumstances) with suits headed by two card combinations like Q-J, K-J, Q-T, K-T, and worst, J-T, where you are not guaranteed at least one top trick.
So in these situations, a Q is acceptable as "one" honor, with the K as the second honor. But if you had J-T behind the Q, and counted the combination as a second honor, the Q-J-T combination would guarantee one top trick.
So are there systems or experts who would allow a bidder to open a "weak two" with a suit headed by Q-J-T, K-J-T, A-J-T etc., counting the J-T combination as "one" rather than two honors?  (With a Q-J-T headed suit, I would want a side honor for a 5-10 point "weak two..")

Broadly yes. A common take on this is ‘Two of the top three, or three of the top five.’  That means QJT counts (or KJT or what have you).  See for example this article on Fifth Chair.
Also note that this only really applies first or second seat, and some would even do it first seat Not Vulnerable. Preempts are getting somewhat more aggressive over time as their value is shown - some even do five card weak twos now, though I find that more risky than I can tolerate.

And if you had QJTxxx or KJTxxx in fourth position, you would pass and find out which of the first three seats had an opening hand, right?

Right, preempts are off in fourth seat entirely. Fourth seat ‘weak’ two is different - still weaker than opener but much stronger and looking for a part score or game opposite ten. https://www.larryco.com/bridge-articles/rule-of-15-and-crifs for example.

"Rules [of thumb] are made to be broken". But "you have to understand why the rule exists so you can effectively choose to break it".  This is what makes them different from Laws and Regulations.
To answer your question straight up, it would be rare to see an expert whose weak 2 agreements in all positions are "2/top 3" (even 2/top 3 or 3/top 5); in fact, it would be rare to see an expert whose agreements in any position (maybe 2nd seat unfavourable) is 2/top 3.  This conservative rule of thumb has been shown to be less effective than a more liberal style.
It's easier to play a conservative style when it comes up; it's trivial for partner to know when to bid game, and when to double the opponents.  It's not that KQ or AQ vs QJT is a trick, it's that partner knows that top-honour-doubleton will solidify the suit (for max 1 loser, 90% of the time), when counting tricks for game.  You can use your limited asking room very effectively.
But it's much easier to oppose a conservative style when they pass and your teammates/the rest of the room doesn't.  The whole point behind preempting is a gamble that because you're weak, the opponents own the hand, and we should take away their room.
Third seat "preempts" have always been some flavour of "he has 13 cards and some of them are spades".  With no worries of preempting partner, hands that are clearly too dangerous to open in case partner has the big hand are clear openers, as are hands that are "too strong" and would be opened at the 1 level if partner could have a hand.
As far as systems go, I submit EHAA.  From the linked synopsis:

An EHAA two-bid shows six to twelve high card points, and a five card or longer suit. There are no restrictions on suit quality (xxxxx and AKQJxxxx both qualify).

Is it a good system?  Well, nobody would play it in a world championship, so no.  But it got us to the second day of a National event, because it puts the opponents to a lot of guesses the rest of the room doesn't have, and if they get enough wrong, even underdogs can do well (of course, our first final session was 35%; if they get enough right, it doesn't matter how good you play).  Obviously, all the system you have over a more normal weak 2 goes out the window, replaced by things that work when partner could have an 8- (or even 6-) high suit.
Less spectacularly, my regular partnerships:

play Precision, and we've agreed "2/top3 or 3/top5 second or vul".  Remember we open most 10-counts at the 1 level, especially 10-counts with a 6-card major;
play "anything goes" in a 12-14 NT context.  First seat favourable, J9xxxx is an expected minimum (and could be worse), second seat all white probably minimum KJ8xxx or QT9xxx.  We play Ogust so we have a hope the few times partner has the hand; we lose on average when she does; we win on average when she doesn't[*];
expects to be the best pair (or second) in the room, and therefore avoids gambles.  We play disciplined first two seats, trusting our defence to get back some of the advantage we're giving to the more freewheeling pairs, knowing we're getting their bad results "for free".

[*]: This is the partnership that plays EHAA when we're bored, challenged to, or when the opponents complain that "we only play all that weird stuff to confuse us".  No, this is what we play when we want to confuse you...

This is not a "rule" but a bidding agreement, and not all partnerships use it. I prefer, for example, to say that a weak two-bid will include "Two of the top three or three of the top five when vulnerable, but any one honor when not vulnerable". Yes I will open 2H on a suit that is Jxxxxx when not-vul against vul. Those who use the Ogust convention to respond to weak two openings are more likely to open with a weaker suit. Ogust permits the responder to ask about suit and hand quality right away, when there is a possibility of game.


text:
Are there times to double for a one trick set in duplicate, when you would not do so in rubber?
In rubber bridge, I would "never" double a part score contract for a one trick set. The reason is that a successful double will increase your score from 50 to 100 if the opponents are not vulnerable, and from 100 to 200 if vulnerable, that is produce a gain of 50-100 points. On the other hand, doubling opponents into game will add a 500 to 700 game bonus to their score, plus 50 in penalties, and double the value of their original part score contract if they make it. The "skewness" of the two possible outcomes argues strongly against a "hair trigger" double.
In match points, a successful double of a part score will increase the penalty from 100 to 200 when opponents are vulnerable, likely enough for a "top" if this is truly a part score battle. It will be a "bottom" relative to other part scores if it fails. But at least the results are "symmetric."
Given the difference between "skewed" and "symmetric" results, are there situations in matchpoints where one would double for a one trick set when one would not do so in rubber?

In very competitive bridge, awareness of when you can double is essential.  When it occurs is most often in match points - not IMPs, where the risks and rewards are more similar to Rubber - and in very specific situations.  But from my experience, midlevel players don't double nearly as often as they should; perhaps for the best in some cases as they don't have the experience to recognize the situation (and I'd count myself in that group for the most part nowadays), but still - they cost themselves not doubling when they should.
In particular, at the higher levels, you should be able to tell what the rest of the room likely is in.  This often occurs when you're facing opponents with unusual conventions, or aggressive opponents.  Say, you're in a clearly comfortable spade partscore (2H, expecting to make 8 tricks comfortably, but not comfortable with the game or even the 3 level), after a slowly developing uncontested auction. Your LHO doubles 2H for takeout, and RHO bids 2S.  (Yes, this is not that uncommon in aggressive play - the "late" takeout.)  This is all vulnerable.
You've clearly got 110 to 140, maybe, and they all of a sudden are declaring, and you're looking at probably setting them 1 - the "cost" in switching from hearts to spades (and switching to defense) is around 2 tricks, in this case.   If you pass, they go down one, and get a top board - that's the point of the interference.  You have to recognize to double here - because of your situational awareness, that the late takeout double will be fairly rare, and most everyone else will be 2H= or 2H+1, and if you are setting 2S 1, you're bottom board!  You could bid 3H of course, but that has its own risks - and if your hand evaluates as perfectly fine on defense, given the point advantage (say you think it's about 22-18), you want to double.
That situational awareness of course also has to recognize when it's a bad idea - when they're not bidding speculatively, but just slowly.
Gavin Wolpert has a good piece on this; in that, he notes first:

When we are entitled to +140 and the opponents compete, scoring +100 just won't cut it. The risk of doubling depends on how many tables have competed to the same level. If we judge that most pairs will sell out and let our counterparts holding our cards make 140, then we must try to protect our equity by getting a bigger plus score.

But then, he shows the opposite:

To demonstrate let's change gears and look at what happens when your opponents bid one more over your 5 level sacrifice. Since most of the field will either play in 4 or double the sacrifice, you will most likely get a near top for +50. If you double them you effectively give up your edge. A plus score of any kind will win the board against all tables which do not find the sacrifice. You will also win the board against all the tables which stop and double the sacrifice. The extra penalty for the double does not help you.

Here the X is tempting, but unnecessary - you already have your advantage over opponents (forcing them to try and make 5); doubling is silly, even if you do think they'll make.
The point is recognizing when it is necessary to protect your part score.  When it is - when you have a solid > 100 points in the bag, and they interfere - you basically have a bottom board anyway if they make, or go down one undoubled, so you have to double.  It's just a matter of experience recognizing those versus the times when it's just a competitive auction and they happen to get in a bit late.

Absolutely! It's a key strategic ploy in competitive auctions.
The key factors that I have always made the decision on is if all of the following conditions are true:

Opponents are Vulnerable, so the one trick set is worth 200 Points. The maneuver is a risky one, and can only be justified if the gain is near certain to get one a top in exchange for the certain Bottom being risked.

We have no further competitive actions available at the Two Level. Attempting to score 110 in a Major, or 120 in NT, has a better risk-benefit trade-off as long as it is available. This usually, though not always, means the Double is made of a Three Level bid.

There is good reason to infer that getting the Undoubled 1-trick set is not just a bad board, but a very bad or bottom board. Worse than 2 out of 12. Converting a passel of 2's and 3's into 0's will ruin a game, so avoid that nonsense.

From the bidding, one knows both where the setting trick is coming from and how the Defense should go. No nonsense making this double and then huddling over Opening Lead - if you don't know what to lead, and how to follow up, this Double is out of place.

Remember that a plus score, especially in a competitive auction, is rarely a Bottom. The key to successful Duplicate Bridge is avoiding the Bottoms - as the Opponents will always throw a Top or two your way. If you can average 7 (or even 6.5) Match Points over 24 or 25 Boards, and then throw in a gift top or two that weren't gifted back, that's a session score of 176 to 182 on a 156 average. That's a successful game.
The key risk with tight Doubles (as with all attempts to create action in the Bidding) is the lack of detailed information. One can more reliably create good scores in the Play, whether as Declarer or Defender. Throwing away a hard-earned overtrick or undertrick on an over-confident speculative Double is not successful Bridge.
Finally, I have known very successful players who occasionally make this for a not Vulnerable set. It's part of their success. But on those occasions when I've been playing up, not once has the remark been made that "I" should have made such a call. I'm looked for and at as a reliable, if not quite regular, partner because I will bid steadily and reliably; find a few extra undertricks and overtricks in the play; and give nothing back unforced.

Update
Reading the comments, there seems to be a presumption that your only option is to Pass or Double.

That's not true. Learn to balance if the Opponents are buying more than 1 hand per session in 1NT, and burying you with them; that's just absurd. Those are your hands. Why aren't you in the auction? Play old-fashioned ASTRO promising a 4-card Major and a longer lower suit if need be. Setting 1NT is hard - harder than making 7 tricks in a 2-level contract of your denomination - so get into the auction.

There will be anywhere from 3 (Good day. Yeah!) to 6 (Bad day. Boo!) where the Opponents are in control. The goal on these hands is to: (1) Identify them; and (2) Get out with an Average Minus. These are not the hands to try for Top or Bottom on; these are the hands to play steady on. Some days you're simply not dealt a possible 200 score.

So it's "never" in rubber and only "rarely" in match points. Under restrictive circumstances: 1) opponents are "sacrificing" by bidding e.g 3 minor over 2 major. 2) You know where the setting trick is 3) Without converting a vulnerable -100 to -200, you are almost as likely to get a bottom or near-bottom as if you tried and failed. Therefore try and (hopefully) succeed.

@TomAu: There will always be part-score hands, every session, where the Opponents are entitled to earn an 8 or 9 if they bid and play correctly. Turning your 3's and 4's into 0's is losing bridge - unless you're getting nearly as many 11's; and those 11's are harder to come by than you realize. Often one pair in the room had a meltdown and gave up 500, so the best you're ever getting is actually a 10, tied with two other pairs. Sometimes you key Declarer's play and turn +100 into -750. Perhaps everyone's down and +100 is a near top. Not every hand is yours - accept it.

The point I was trying to make was that this is at least "permissible" in matchpoints, but "rare" even then .I wasn't thinking every hand, or even every other or third hand. Maybe every eighth or tenth. But those "eighths" or "tenths" add up to two or three hands a session. The other thing I got from your comment is that you wouldn't double if you thought you could get 2 points out of 12 by not doubling. That would imply that you are only "risking" 1's or 0's against "top or bottom, which would have a weighted average value of 4-6 out of 12.

@TomAu: Half that - once per session is more typical. There will always be 3 to 6 hands per session where Opponents - not you and Partner - have control in the Bidding. Attempting to control those hands is how you end up with a 35% game. Let them go, and try to get the extra trick in the play to salvage Average-Minus. If there's 6 such this session, it's just not fated to be a brilliant session. Play solid; go home with your 170 or 175; and look forward to the 'morrow. A session where Opponents are in control only thrice will come by; and that's the session to try for 200.

I think this is right, for the most part, at the club level.  I don't think that you can assume, for example, that a plus score, especially in a competitive auction, is rarely a Bottom in the higher levels of competitive Bridge; plenty of times there you'll see auctions where 25/30 hands are 1N= +90, and your opponents happen to play an odd 1N  system that happens to end up in them declaring 1N instead, for -1.  You double (+100=good board) or you don't (+50=bad board).  In club bridge you just don't have that kind of consistency, so reliable positive is more important..

@Joe: From club game to Regional Flight A, I rarely encounter a hand where +50 scores lower than A-. It's just not that common - if you're playing well. And if you're not plating well - then there is far more wrong with your game than neglecting to double the Opponent's part score for +100.

@ForgetIwaseverhere I must have played different hands than you... it's fairly often that -50 is well above A+, in my experience, in higher level competition, and even if you're right that +50 is A-, at the higher levels turning those A- into A+ (or more) by doubling is key to a good final standing.  It becomes something you (must) learn how to recognize, when a hand undoubled will inevitably be a poor score, and when doubling it is necessary to make it good - but it does happen, fairly often in my experience (and far more often watching the better players I've known).


text:
When are good times to build early roads "inland" in Catan?
In most cases, it is a good idea to build early Catan settlements, close to, but not on the coast, and then build roads toward the coast. This has the dual advantages of 1) heading toward key ports, and 2) minimizing conflict with other players, and the resulting wasted effort.
Like every rule, this rule probably has exceptions. Which might they be? For instance, might it make sense for both settlements to point their roads toward each other, aim for a "connection" (and intervening third settlement), and later on longest road?

This is a pretty open-ended question, as it's very situational and depends on lots of things such as play style, board setup, other players placement, resource distribution, etc. With that in mind, take this answer with a grain of salt.

In most cases, it is a good idea to build early Catan settlements, close to, but not on the coast, and then build roads toward the coast

Assuming that the number tiles are somewhat fairly distributed, I'll usually try and take this strategy and place my second settlement (in the snake draft) such that I can build one road and my third settlement to be on a port.
Some of the exceptions to this might be:

Crowding. If the folks you are playing with are hogging the coasts and leaving the middle more bare, forward settle them. You'd have the advantage of potentially blocking them from moving in towards the island, which could keep tiles for yourself.
Attempting longest road. As you briefly mentioned, it may be in your best interest to start building wide and connect your empire. I'd say this is rare (going for longest road over preferable resource placement), but certainly not impossible. Especially if you're going 4th, you can potentially guarantee connecting your initial settlements early on. Personally, I've found it better to not ever go into the game planning longest road. If it comes around as an opportunity later in the game, great. If not, then there are plenty of other ways to get VP's.
The number tokens are not well balanced. If you do not place the number tokens in the recommended pattern (or place the desert in-between two outer edges which would offset the tokens), then there might be a particularly good spot (e.g. 6-8-4) that would probably supersede shooting for a coast.

A bit late to the case, but you're not allowed to have 6-8 hexes next to each other, it is stated in the rules.


text:
In Diplomacy, is it possible for an army to be convoyed by two countries if both write the appropriate orders?
There are numerous possibilities, but this one comes to mind. Italy and Austria are allies in a "Lepanto" opening (against Turkey). In the spring of 1901, Italy moves a fleet, Naples to the Ionian Sea, and Austria moves its fleet, Trieste to Adriatic Sea.
In the fall of 1901, Italy wants to move an army, which "held" in Venice in the spring, to Tunis. Austria agrees to convoy it through the Adriatic Sea to the Italian fleet in the Ionian Sea, from thence to Tunis.
So Italy writes: "Army Venice to Tunis, via convoys in Adriatic Sea and Ionian Sea. Fleet Ionian Sea convoys Army from Austrian fleet in Adriatic Sea to Tunis."
Austria writes, "Fleet Adriatic Sea convoys Italian army in Venice to Italian fleet in Ionian Sea."
Is this a valid set of orders, and will it achieve the desired result?

It is possible for an army to be convoyed my multiple countries (although you should write the orders differently than you did in your example).
First, the relevant rules:

Convoying an Army Across Several Water Provinces
If Fleets occupy adjacent water provinces, an Army can be convoyed
through all these water provinces on one turn, landing in a coastal
province adjacent to the final Fleet in the chain.
In Diagram 20, the English Army from London goes to Tunis on a
single move with help from the French player.

Italy would need to write the orders:

A Ven to Tun
F Ion convoys A Ven to Tun

And Austria would write the order:

F Adr convoys A Ven to Tun

From the rules:

Writing Convoy Orders
Just as “S” indicates support, the letter “C” is used to indicate convoy.
Following is an example of a convoy order:
A Ank–Sev; F Bla C A Ank–Sev

The reason for this is that you can potentially issue multiple convoy orders:

An Army convoyed using alternate convoy orders reaches its
destination as long as at least one convoy route remains open.
Orders can be written to permit more than one route for convoying
an Army from its origin to its destination. The Army isn’t prevented
from moving unless all routes in the order are disrupted.

An important consequence of this is that you can not write a convoy order that is contingent on the convoy route.  If you have army in Rome and write A Rom-Spa, F Tyn C A Rom-Spa, from an agreement that you will be convoyed through Wes that order will go through if there is a fleet in GoL that convoys.

That idea is allowable, but the exact phrasing is slightly off.
Italian orders:
Army Venice to Tunis;
Fleet Ionian Sea Convoy Army Venice to Tunis;
Austrian orders:
Fleet Adriatic Sea Convoy Army Venice to Tunis;

No, those orders are not valid. Italy's orders for their army in Venice would be
A Ven-Tun
That's it. There is no room in the syntax for specifics about how that will occur, so the "via convoys..." makes no sense.

ETA:
The fleet orders must match the army orders, and "army from ____ sea" is not valid.

This is rather pedantic. "A Venice to Tunis" is a valid order, it does not have to be fully abbreviated.

@Caleth - on the contrary, pointing out that the full city name can be used instead of the abbreviation is pedantic; I pointing out an essential flaw with the case that Tom presented.

There's no flaw. There is additional text that does not introduce any ambiguity in what the orders are.

@Caleth I am not so sure about that.  The via formulation seems to imply that your orders has a requirement that you are not allowed to put on the order.  (Ie. you are not allowed to specify the actual route of the convoy)

@Taemyr so? As long as there is at least one complete route, the order resolves

@Caleth I am not comfortable that any judge would interpret "An order that has only one meaning" to be "An order that has only one legal interpretation"