How exactly do time and "tense" work in Mandarin REALLY? I am trying to figure out what the most proper way for one to say something simple like if someone asked, "How do you know that?" and then I say, "I read it in a book". Now what I'm wondering about is how you translate that "I read a book" clause into Mandarin.

See, the "read" here is a past tense, and apparently, in Mandarin, there is no "tense" marking. Time, it seems, is indicated by putting a time adverbial before the verb. Yet here there is no specific time, rather it's at some indeterminate past time, the only thing known is that it happened. My best guess from various reading material was to try something like,


  我以前看一本书 (wo yiqian kan yi ben shu),


but that seems to my ear to lay really heavy emphasis on the "past"-ness of this action, when that is not the primary point here, the point is the fact of having read the book.

So what I really feel I want to do is to use 了, as in


  我看了一本书 (wo kan le yi ben shu)


But then I hear that 了 "is not a tense marker", "has nothing to do with time and nothing to do with tense" and stuff like that, and that what it really indicates is "completion". Yet the English sentence has tense. So is the above the correct way or not? I also think that the first sentence I mentioned should be 我以前看了一本书 (wo yiqian kan le yi ben shu) as well, but there the 了 seems less troubling to me because we have the time specified and in the sentence 我看了一本书 given out in this context it seems to my ear that 了 is acting like a tense marker, setting up a contradiction. Without 了 I get


  我看一本书 (wo kan yi ben shu)


which sounds to me more like "I read [pronounced REED] a book", but then again I've heard that tense/time can be inferred from context.

If the form 我看了一本书 is correct then what role is 了 playing here and why does it sound to me like past tense with a not-a-tense-marker indicating tense?

If none of these are correct, what, straight up is the correct translation? I've found it really hard to find something that just straight up answers that.

(Also, I'm not 100% sure if the counter 一本 indicating the singularity of the book is needed or correct in all these either but that's a separate question! This question is about time/tense not measure and I'm just using that as an example of something where I think the time is not indicated elsewhere in the conversation by any grammar feature.)
If the form 我看了一本书 is correct then what role is 了 playing here and why does it sound to me like past tense with a not-a-tense-marker indicating tense?

'了' in &quot;我看了一本书&quot; is a [aspect marker] indicating completed action.

我看一本书 = I read a book

In 我看了一本书,  the action '看' is completed, which imply 看 is not in present tense but in past tense.


Also, depend on the context, [verb + 了] could indicate :

[present perfect tense] 我刚看了一本书 = I have just read a book
[past perfect tense] 我昨天看了一本书 = I had read a book yesterday
[future perfect tense] 我明天会看了这本书 = I will have read this book tomorrow.

'过' in &quot;我看过一本书&quot; is a [particle] marking experiential aspect

我看一本书 = I read a book
我看过一本书 = I had read a book (I experienced reading a book, that indicates 看 is in past perfect tense)

*I think I answered a similar question How do you specify past tense for 是?

If no time reference is found in the context, then all verbs are in present tense by default.
When you are reading a historical novel, even most individual sentences in it didn't have time reference, you should still know it is in past tense; If you are reading an instructional manual, you know the text is written in present tense entirely.

Edit:

Mike3 comment:
OK... now I'm not entirely clear on the difference in meaning between &quot;我看了一本书&quot; and &quot;我看过一本书&quot;. Is it just that one emphasizes something else (completion vs. experience) or what? Which would be the correct one to use in the scenario I mentioned in the question and why?

In your scenario:
Q: &quot;How Do you know?&quot;
A: &quot;I read a book&quot;
you can use &quot;我看了一本书&quot; or &quot;我看过一本书&quot; for &quot;I read a book&quot;  in this scenario.

&quot;我看了一本书&quot; stated the fact that you finished reading a book in the past. (了 emphasizes the completeness of your action)
&quot;我看过一本书&quot; stated the fact that you had in the past read a book (过 emphasizes the action was in the past).

Both sentences stated the source of your knowledge is from reading a book. '看过' is more preferable if you want to emphasize the action happened in the past.
As I mentioned, depend on the context, '看了' can be in any perfect tense.