text:
What is the substantial cause of an instance of consciousness?
Context: I'm considered a skeptic of rebirth in my tradition which is the Gelug branch of Tibetan Buddhism. I'm asking this question to help me understand what other traditions think. In my tradition it is believed that rebirth is a semi-obscure phenomena the truth of which can be fully known through reasoning alone. I have a hard time understanding how and do not find any line of reasoning I've heard to be particularly convincing.
The strongest reasoning I've seen others in my tradition give for rebirth is that each instance of consciousness must have a substantial cause. And that brain/matter cannot be that substantial cause because brain and consciousness are fundamentally of two different natures. Therefore, each instance must have been proceeded by a previous instance as its substantial cause leading to an infinite regress/progress back/forward in time.
Here is an excerpt from His Holiness the Dalai Lama's book - Kindness, Clarity and Insight - where he briefly summarizes this reasoning:

"... the nature of
  the mind is mere luminosity and knowing. Mind is something that has
  the capacity of appearing in the aspect of whatsoever object through
  the force of the object’s casting its aspect to it and is an entity of
  mere clarity and cognition, with a nature of experience. It
  disintegrates moment by moment. However, among its many
  causes—classified into substantial cause and cooperative conditions—it
  must, as an entity of conscious experience, have as its substantial
  cause an immediately preceding cause which is a former moment of consciousness. It is not
  possible for an entity with the character of luminosity and knowing to
  be produced from external material elements as its substantial cause.
  Similarly, an internal mind cannot act as the substantial cause of
  external elements. Since each moment of consciousness requires a
  former moment of consciousness as its substantial cause, there is no
  way but to posit that the basic continuum of mind is beginningless.
  Some specific types of minds [such as desire for an automobile] have a
  beginning and end, whereas other types [such as the ignorance
  conceiving inherent existence] have, in terms of their continuum, no
  beginning but an end. However, neither a beginning nor an end can be
  posited to the mind of luminosity and knowing. Therefore, although
  mind disintegrates moment by moment, its continuum is beginningless."

I believe this reasoning is basically equivalent to Chalmer's Hard Problem of Consciousness. To be clear, I think it is a hard problem for scientific reductionists who believe that consciousness can be reduced to physical matter and energy arranged in a specific way.
On the other hand, it is also equivalent in a different formulation to another famously hard problem: Descarte's famous mind/body problem which assumes the dichotomy of mind/body above and then asks if these are of such fundamentally different natures, then how do they interact? It would seem that positing any mechanism of interaction would betray the original assumption: that they are so fundamentally different that one could never give rise to the other... that they could never touch if you will.
Which leads to the question: what is the substantial cause of an instance of consciousness?

Mind
Matter
Both
Neither
Pineal gland did it!

Would prefer answers with reasoning to help me understand.

BTW, if you are unfamiliar with this problem from a Western philosophical perspective see here: https://plato.stanford.edu/entries/dualism/

I marked the question down & voted to close it because it is not related to Buddhist philosophy. The question is about biology or neurology where as the Buddhist teaching is about how suffering arises & how suffering ceases.

It is actively talked about and discussed by people who believe they are speaking about Buddhist philosophy including ordained members of the Sangha so I'm not sure how/why you think it unrelated to Buddhist philosophy.

My comment was clear. The Buddha said he only teachings about suffering & its cessation (MN 22)

You mean, "he only teaches" rather than "he only teachings", right? His Holiness the Dalai Lama has explicitly taught about this subject. You seem to have an idiosyncratic idea about what constitutes Buddhist philosophy.

The Dalai Lama often follows Tibetan ideology. Also, if the Dalai Lama could answer your question, why don't you simply find an answer from the Dalai Lama?

Yeshe Tenley, I'm not sure what (or who) you're asking: are you asking for an orthodox answer e.g. according to what the Dalai Lama taught? Or are you asking everyone for their personal opinions? Are you only asking for answers from people who do, or who don't, see this as a reason to give for "literal rebirth"? Or only asking people who have learned the "Western philosophical perspective" you cited?

Hi ChrisW, I'm asking all Buddhists who believe they know the answer and to provide reasoning to support if possible. My reference to the Dalai Lama was only in reply to whether this question was legit in the context of Buddhist philosophy: ie, it was meant to proffer evidence in support.
I'm not really sure what the Dalai Lama would answer nor what his reasoning would be, but if he reads this I would be very interested in his answer as well :)

i think you should explain what you mean by substantial cause, which is a term i had forgotten or was not familair with. i mean, in most english language interpretations of buddhism substance is closely linked to self and svabhava

You can see below Tenzin Dorje’s answer which has the definition of “substantial” which I don’t think has the implication of “substance” as you are thinking, but not sure.

The cause of suffering is avijja. The choice to avoid uncomfortable truths. Nibbana, the total end of suffering, can only be attained by summoning the courage to conquer this weakness and striving to see things as they actually are. The uncomfortable truth is that clinging to views which are not supported by evidence is a coping mechanism for suffering which keeps us locked into the cycle of suffering.

In his commentary to Kamalashila's Stages of Meditation, His Holiness the Dalaï-Lama lists 5 types of causes:

All those phenomena that  are produced at some times but not others
  depend on causes and conditions, and they are of various types. Causes
  are of different types, such as (1) substantial cause, (2) direct
  cause, (3) indirect cause, (4) cause of equal state, (5) concomitant
  cause, and so forth.

He gives a definition of substantial cause:

[A substantial cause is] A cause that primarily produces its result as its
  substantial continuity; e.g., production of a sprout from a seed.

In 'Kindness, clarity and insight', HHDL says:

It is not possible for consciousness to be produced from matter as its
  substantial cause. Once consciousness is produced from a former moment
  of consciousness, a beginning to the continuum of consciousness cannot
  be posited.

In addition, in 'Consciousness at the Crossroards', HHDL gives an interesting line of reasoning establishing that matter (form) is not the substantial cause of awareness:

Specifically, the awareness must have a substantial cause. Now if the
  substantial cause of awareness is matter, then why is it that some
  things have no consciousness, and other things, such as animals, have
  consciousness?

In Pali and Sanskrit, 'substantial cause' is Upādāna. Regardless of contexts where it refers to specifics, literally it translates fuel. The Tibetan for substantial cause is nyer len.
In 'Buddhist Philosophy: Losang Gönchok’s Short Commentary to Jamyang Shayba’s Root Text on Tenets, by Daniel Cozort and Craig Preston, Jamyang Shayba says:

Because of being a mind, it is established that [another mind]
  precedes it.

And Losang Gönchok comments:

The subject, a knower [i.e., a mind] just after conception, is
  preceded by a mind that is its substantial cause because of being a
  knower. The subject, the final mind of death of a common being, is
  able to generate the mind that is its impelled object because of being
  a knower having desire, such as a prior main consciousness.

With respect to the ancillary topic (rebirth) it says:

Because of movement [to activities immediately after birth] and memory
  [of former lives] also, [the existence of former lives is
  established]. Moreover, since a calf who has just been born seeks the
  milk of the teat and since with respect to animals, etc., the mind
  moves to activities of eating grass and engaging in desire without
  being taught, one can understand that this is done due to the
  conditioning of previous lifetimes. Also, memories of former lifetimes
  exist, and matter cannot act as a substantial cause to produce
  consciousness.

this answer is much better than mine!

Since you asked for personal responses with reasoning, I feel I can just answer in my own words, not quoting scripture or teachers. And yet I believe my position is in line with the view of the realized. In fact this time I will go as far as to say that I know and see directly, and the only constraint on sharing this is my ability to communicate or our ability to understand each other.
I understand your question, and I see multiple parts to it, or several assumptions that you make.
First, about mind/matter dualism, it is absolutely clear to me that these relate as information and it's media. Which basically translates to, they are not the same, neither are they separate. In context of existence at large, information is inherently connected with causation... and energy... This is to say that information, causation, and energy are different aspects of the same thing. Of the two sides, information and media, the media or matter is not primary. We could say, information is primary, as it shapes, transforms and animates matter. Perhaps we could even say, information-energy is all that exists, since in one sense matter, when looked at closely, is nothing but energy all the way down. This information-energy principle is what gives rise to mind.
Here's how mind arises from the continuum of dynamic information-energy permeating the universe. Because information moves over matter as it's media, and moves non-linerarly in various directions, it shapes and influences its media in different ways. This process carries some patterns across, leaving imprints, or something like informational echoes. This gives rise to representation - an ability of information to reflect or represent. As parts of the universe interact, they leave imprints on each other, carrying the echoes of information, representing the shape of the interaction. This representation of information by information is what we call mind.
Mind not always exists in conscious form; 99% of it is thin and subtle, manifesting as astronomical, geological, and biological phenomena. Only in sentient beings mind gets condensed enough to give rise to consciousness, or full-blown experience of a world. Consciousness is the mind's nature of representation taken to its pinnacle.
So when you ask about causes of consciousness of a sentient being (defined here as experience, or dynamically maintained model of existence), it is present mind (here defined as information's representation capacity) plus past mind (stored representation, or memory), plus interaction or exchange of information over media between the locality of the sentient being and the rest of the world. In other words, the cause of an instance of consciousness is mind, and the nature of mind is dynamic information. This dynamic information is a process of exchange and transformation that has no logical beginning.
This entire description is limited in its dependency on the notions of time and space. Strictly speaking, time and space are creations of mind in its modeling activity. In reality the structure I described above is a multidimensional network that in its complexity goes far beyond "space" and "time", and has some holographic aspects, but from the perspective of individual consciousness with its observation of locality, time and space seem to exist. But we are at limits of speakable here, so I won't talk about this much.
Anyway, what's useful for us, Buddhist practitioners, is to realize that mind is not special, but that in fact it permeates the normal fabric of things, and that it's interactions come to us from beginningless times. So in some sense we (the sentient beings with our minds) are the result and the legacy of the same beginningless process that gives rise to stars and Buddhas. We are of the same nature, we are continuation of the same thing. Each of us is a holographic locality of the rest of the universe.
What this means, is that Enlightenment has nowhere to hide from us. Our nature is Buddha nature, and has always been unstained from the beginningless times. This also means that consciousness, or experience of the world, is a very crude model, a contrived representation that we assumed to be real and accepted as our prison. We are stuck in our own mind, taking its models for real, and spinning in a circle of reaction, frustration, pain, and fake goals, which keeps us maintaining the same picture of the world. A particular picture of the world, contrived and maintained by the mind stuck in a negative self feedback loop is called (contaminated) experience or consciousness.
The cause of this experience of a world is ignorance (of the fact that this experience is mind made) and the self-maintaining loop of pain, frustration, and action that comes from taking this world for real.
At the end of the day, this entire story, including ignorance, and waking up from ignorance, is just the way things work, so everything is perfect in its completeness, and there's no reason to feel bad about the illusion of the world we live in, since creating illusions is the nature of mind. But perhaps, with greater understanding we can be free to stop maintaining the worst nightmares we dream to ourselves, and experience the meta-reality from a wider range of perspectives.
This is probably the most out of line answer I ever gave, so I apologize if this goes too far outside topics we normally deal with on this site. I hope you can relate to this from the perspective of Buddhism, at least in my mind it all connects and makes sense together.

Hi Andrei, I think this answer is most appropriate and probably does the best job responding to what I was looking for. I have also seen your other replies and answers on similar topics and find that our views are pretty closely aligned. That said, I think this answer is essentially refuting what my teachers say or at least I think their is daylight between this view and theirs. In other words, this answer does not posit that the truth of rebirth can be deduced through reason alone. Would you agree?

Hi Andrei, your answer is intuitive, and the way you have presented it here is quite remarkable. I enjoyed reading it and I respect your view. But the phrase "Mind not always exists in conscious form; 99% of it is thin and subtle, manifesting as astronomical, geological, and biological phenomena." made me pause. The Buddhist definition of mind is that it is culmination of feelings, thoughts, ideas, intuitions etc, which doesn't bode well to your quote above. Just wanted to get your insight on the above quote. Can you please elaborate?

Thanks! Not sure where you got that definition of mind as culmination of feelings, thoughts etc. - certainly not in suttas. Then again, when we say mind we need to be careful since it's a very overloaded term. Here in the answer I spoke about the basic mind element as opposed to the higher order phenomena such as the human consciousness. Basic mind element is mere representation, for example as a star's spectrum carries a representation of its chemical composition, or an impact crater's shape carries a representation of the asteroid's size and speed.

The inanimate nature is full of information exchange, interactions carrying representations, with their impact accumulating, developing into tendencies. These then serve as the building blocks for the so-called Life which is just a more developed level of tendencies and in-turn their interactions carrying their representations.
E.g. a set of volatile organic compounds emitted by a flower is a representation of its nectar's content, including sugar, and ultimately of its genetic makeup (a specific self-reproducing cyclical tendency). The bee is an instance of another cyclical tendency...

The bee picks up on the scent and collects the nectar - and here we have the basic mind at play. Human mind is just more of the same. Buddha defines "distinguishing mind" (vijnana) as something that develops from accumulation of "tendencies" or "latencies"(samskaras) - which is exactly what I described above. Sorry, this must be difficult to follow, I'm trying to be as clear as I can but it's not an easy subject to explain in a few comments.

One more thing, further to this answer:

a view of life -- developmental neurology

... and this answer ...

Frankly, that's an awful argument that would be laughed out of any undergraduate class

Without wanting to be rude to the teachers, I'm quietly sympathetic to the latter statement, i.e. I too was not persuaded by the argument as an argument.
Perhaps, if you want to accept it, you shouldn't see it as an argument, not as a  proof, but rather as a description of what is.
I learned (from my Physics teacher) that you choose a (scientific) theory because it's useful -- e.g. it isn't contradicted by observations, and it makes useful/accurate predictions about future observations. Sometimes there are different mutually-contradictory theories, which are useful in different circumstances (e.g. sometimes electrons are "like a wave" or sometimes "like a particle" depending on the type of experiment -- so you sometimes choose one theory and sometimes another, depending on which problem you're trying to solve, or which observation you're trying to explain).
The Theory of Gravity for example is useful for predicting planetary orbits. It's not, so far as I know, any good at explaining why people love each other. I'd thus describe the Theory of Gravity as a "right view" when you're calculating planetary orbits ... and it's a "wrong view" when you're explaining why people love each other!
So perhaps you shouldn't separate, can't afford to separate, the explanation from the reason for the explanation (i.e. its purpose, the use to which it will be put).
The "developmental neurology" I mentioned ... I mentioned it because you asked about the origin or substantial cause of consciousness: and maybe that (the book I referenced) was a fair description of how "consciousness" might start, grow, develop. To that extent it may be a right view of the development of consciousness in a person.
In my opinion, though, it's something of a "wrong view" from a Buddhist perspective:

Firstly, because it's easily mistaken for a materialist view ("neurology" implies you're observing physical neurons and encourages you to overlook the effects of experience and even of intention);
More importantly, because (in my experience) the theory doesn't help solve the important problems at hand, for example questions about ethics or about dhukkha (or about "self").

I find that the "neurology" view isn't just useless to me1, it's even counter-productive, if I try to apply it to the kinds of circumstance -- e.g. post-natal existence :-) -- for which Buddhist doctrine is helpful.

My main study at school was actually Maths not Physics. IIRC Maths doesn't try to prove everything. Progress in Maths depends on making or accepting assumptions (called an "Axiom)", and then saying, "given this axiom, what further theories can we prove?" Or conversely, "In order to prove this theory, what axioms do we need to assume?"
I think there's no shame in treating some statement as axiomatic -- I guess2 that doing so is inherent in any attempt to use logic. For example, a Syllogism depends on "premises".
Quoting from this answer again:

I mean, you seem to beg the question that consciousness has a substantial "cause", and then beg the question that it cannot have such a "cause", and then infer that it must, then, be eternal. Really, it should just show you that one of your assumptions is wrong.

I think there's a limit to what you can "prove" using logic (in particular it's difficult to prove the premises you're using) -- on the other hand logic can be helpful.
In summary, when you're studying at a school like this one3  perhaps it might help (to understand what's being taught) if you were to see statements about rebirth as being axiomatic rather than proven, and see whether you derive useful results from those axioms.

I wonder if the first three of the Four Noble Truths are another example of a logical syllogism:

Definition of Dukkha is an axiom
Craving as the origin of Dukkha is an axiom
Cessation of Dukkha with cessation of Craving is a logical conclusion from these axioms

My logic tells me that:

The first two are acceptable, plausible, axioms, which I can fit to my experience.
The third would be useful if true, is based on reasonable logic and on plausible axioms
The third is therefore a theory that's worth considering: i.e. to experiment with, to test, to see whether it's true (i.e. to see whether you observe the effect predicted by the theory).

You wrote in a comment:

To my mind, belief in rebirth requires faith but I know others disagree.

So far as I know, any logical statement ultimately rests on some premise[s] or axiom[s].
You may, or may not, want to describe that as "requiring faith" (see also faith).
You can try to prove an axiom by appealing to further axioms (e.g. prove rebirth by assuming something about substantial causes) -- ultimately it's turtles all the way down -- so (instead of hoping for some ultimate proof) you might want to depend on assessing what you'd consider sensible4, useful, ethical.

I'm not sure but the fact that logic is like this might be related to how or why some schools describe everything as "empty"?

1 (I'm not a neurologist myself, so no wonder I get little insight from it; I don't want to disparage neurologists' work either)
2 (I'm not sure, because I'm not a philosopher either)
3 (I say this without understanding what that school is teaching, and why)
4 (sanditthiko akaliko ehipassiko opanayiko paccattam veditabbo vinnuhi -- see also this answer)

Hi ChrisW, as someone with a background in physics and math I am sympathetic to your answer, however my teachers say that the truth of rebirth can be arrived at through pure reasoning and that it is not dependent upon any controversial axiom. As I have explained, I have problems understanding how, but I don’t necessarily think that means they are wrong. In other words,  I have great deal of respect for them and thus leave open the possibility they are right and I just have an obstacle to overcome.

the truth of rebirth can be arrived at through pure reasoning Kant wrote something about that, if that matters. But, even without "axioms", perhaps there are "definitions"? If your mother points at something and tells you, "that's a cow!", that's not a reasonable but a definitional one. So might it help (help to accept) to see more of the statements as definitional rather than reasonable or logical? And IMO sometimes you're in class not to learn about the world but to learn about (to study) the teacher, and how the teacher reasons.

I'm not saying that the reasoning my teachers posit is free from axioms or definitions, just that the axioms are uncontroversial and the definitions rather common :) Again, I myself admit to being unable to arrive at the conclusion that they say is evident. However, I am as yet unwilling to conclude that I am right and they are wrong. In the meantime, I take it on faith and strive to understand their reasoning and to try and look deeper.

What is the substantial cause of the wetness of a wet cloth?
Is it water? Or is it the cloth? Or is it your hand touching the cloth and ascertaining that it is wet?
There is no single substantial cause for wetness. Similarly, there is no single subtantial cause for consciousness. It arises out of the complex interaction of other factors, which is covered under dependent origination.

Hi Ruben, I am sympathetic here as I also have a hard time understanding how to reduce an infinite series of dependencies for any phenomena into a finite number of causal conditions and labeling one of them the “substantial” condition.

I'm not sure if this counts as an answer, but ...
I think that some (other) people ask a similar question, to "prove" the existence of God. They argue that, "If something (i.e. the universe) exists then someone (i.e. God) must have created it. If the universe was created by the Big Bang, then what created the Big Bang? The answer is, 'God'."
They point to some infinite chain of causation, assume there must have been a "prime cause", and call that prime cause "God".
You seem to be arguing something similar -- "a cause for consciousness isn't evident, therefore present consciousness must have been caused by a previous consciousness, reborn from a previous life." Is that a fair summary of the argument?
So far as I know, the Buddha in the suttas doesn't answer that question. There's a sutta (Assu Sutta (SN 15.3)) translated as

At Savatthi. There the Blessed One said:

"From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. What do you think, monks: Which is greater, the tears you have shed while transmigrating & wandering this long, long time — crying & weeping from being joined with what is displeasing, being separated from what is pleasing — or the water in the four great oceans?"

The beginning is called "inconstruable" and you leave it at that, and return to a more important topic.
See also The unanswered questions.
As a former mathematician I distrust attempts to "prove" things by reasoning about "infinite" series (e.g. Zeno's paradoxes) -- IMO they prove nothing except that logic is untrustworthy -- that kind of reasoning doesn't really prove the existence (or non-existence) of God ... nor of literal rebirth.

To answer the question ... I don't know, a friend of mine once gave me The Blank Slate which I thought was good. I think it claims that the brain (when it's born) has some built-in structure (the optic nerve and what that connects to, for example), and then learns to see (and eventually to be "conscious" of what it's seeing, e.g. to discriminate between different sights, to associate other experiences and feelings and so on with various sights, to recognise objects, and so on).
But although that is a view of life (I'm not sure what to call it -- developmental neurology perhaps), I don't think of it often: it's a view, but not an important one. I mean, you can consider it important if you want to ... but I think, my experience is, that this a topic which I am only able to classify into the "thicket of views" category.
To try again to answer the question, I suppose the cause of present (adult) consciousness is some combination of sensory contact with (learned or stored) past experience.

(There's a lot of literature that I'm not familiar with, including Tibetan Buddhism, the Abhidhamma, and David Chalmers.)

Hi ChrisW, I had assumed (apparently wrongly) that other Buddhist traditions besides Tibetan buddhism believed two things:

That the truth of rebirth is a semi-obscure phenomena that can be known through reasoning alone

That instances of consciousness require a substantial cause - for without a substantial cause this is akin to saying that instances of consciousness arise from nothing at all and are not subject to karma

I will update my question stating explicitly these assumptions and followers of other traditions can answer accordingly.

I had assumed (apparently wrongly) Not wrongly -- for all I know, you may be right -- I suppose some people do believe these things, or argue that way. I wasn't trying, in my answer, to explain the belief of a tradition -- only my own view. I thought this topic was a follow-on from a previous question about 'secular buddhism' -- I think you were implying that the argument (about cause) is solid logical proof of literal rebirth -- I don't understand it to be a solid proof, and maybe not even a useful or answerable question.

Ah, no this question is not related. In fact, I have trouble following this reasoning and do not see how it is sound. In other words, my tradition - Gelug branch of Tibetan Buddhism - regards rebirth to be a semi-obscure phenomena that can be known through reasoning alone. I assumed this was a widely held belief among other traditions as well. I asked this question to explore reasonings to hopefully understand why teachers I respect say this can be known through reason alone. To my mind, belief in rebirth requires faith but I know others disagree. I wanted to know their reasons.

According to a quick google search, it seems that HHDL is using Dharmakriti's argument for rebirth, supplemented with the idea that mind and matter are not absolutely divided, that reality is in fact indivisible. I would just want to raise two points wrt your question:

what exactly is a "substantial cause"? Once you have that you can work out whether every moment of consciousness is preceded by another moment of consciousness as a substantial cause. What's important is that you do so without begging the question.
I don't think Descartes thought that reality is indivisible. Descartes is engaged in a specific metaphysical project to describe the nature of "reality itself", and in doing so he says that mind and body are "really distinct". If in reality itself mind can exist without body, and vice versa, then it is wrong to say that reality is indivisible, whether or not reality is divided.

If you want to ignore the more subtle differences between philosophical arguments it seems a bit like 1st cause argument for God, except God is replaced with the self.

Oh??!! I did not know this argument was originally Dharmakirti’s argument! That is very helpful and gives me something to research... especially as Dharmakirti often gave arguments from non-Prasangika tenet system. Thank you very much for this!!

@YesheTenley thanks! and you agree with point 1, right? i think that's the key to understanding the "argument", and i can't see of any other way one could proceed with it

I think right now I agree that premise 1 as you have above seems to be begging the question. IOW, it seems the definition of “substantial” seems to be doing a lot of the work in this reasoning and I have doubts whether the definition is sound or whether it is ill-defined. It looks like a tautology...

This is my apostate explanation in answer to your question, founded within my meditative practice, not my scholarship (phd). It’s too long to quote here, but it’s not TL;DR for someone with your obvious rigor, Yeshe Tenley. Please accept it in that light.
https://bit.ly/BreakingTheMirror

Karma is the direct cause of consciousness. When light hits the eyes, the eye consciousness arises as a result of past Karma. When the sound hits the ears, ear consciousness arises as a result of past Karma.
But except for the case of mind consciousness, the physicality acts as an indirect cause for the consciousness to arise as every sensory experience except the mental experiences consists of both mental and physical aspects.
Regarding rebirth, it is the materialists who need to provide evidence that all experiencing cease at the moment of death. What we call death is really a concept. You have no firsthand knowledge of death. But you have firsthand knowledge that after every experience, another experience arises. You have no direct evidence that experiencing is ever going to stop. So why throw away your first hand knowledge in favor of a concept you have no direct knowledge of?

SN 12.25 says there can be no kamma without contact.

SN 12.25 :"The Blessed One, my friend, has said that pleasure & pain are dependently co-arisen. Dependent on what? Dependent on contact." Pleasure and pain are Vipaka(result or Karma). Not Karma itself. You got it confused.

Whatever brahmans & contemplatives, teachers of kamma, who declare that pleasure & pain are self-made, even that is dependent on contact. Whatever brahmans & contemplatives, teachers of kamma, who declare that pleasure & pain are other-made, even that is dependent on contact. Whatever brahmans & contemplatives, teachers of kamma, who declare that pleasure & pain are neither self-made nor other-made, but arise spontaneously, even that is dependent on contact.

@Dhammadhatu that simply explains pleasure and pain are not created by a self or entities other than self. Karma has nothing to do with a self. It's a mere causes and effect process.

The Pali suttas often mention 'consciousness' because consciousness is one of the five aggregates clung to as 'self'. It is the absolute Law of Dhamma that such clinging will always bring suffering, as described in the following sutta, which uses the metaphor of a 'thief' for clinging:

And how is the nutriment of consciousness to be regarded? Suppose
  that, having arrested a thief, a criminal, they were to show him to
  the king: 'This is a thief, a criminal for you, your majesty. Impose
  on him whatever punishment you like.' So the king would say, 'Go, men,
  and shoot him in the morning with a hundred spears.' So they would
  shoot him in the morning with a hundred spears. Then the king would
  say at noon, 'Men, how is that man?' 'Still alive, your majesty.' So
  the king would say, 'Go, men, and shoot him at noon with a hundred
  spears.' So they would shoot him at noon with a hundred spears. Then
  the king would say in the evening, 'Men, how is that man?' 'Still
  alive, your majesty.' So the king would say, 'Go, men, and shoot him
  in the evening with a hundred spears.' So they would shoot him in the
  evening with a hundred spears. Now what do you think, monks: Would
  that man, being shot with three hundred spears a day, experience pain
  & distress from that cause?
Even if he were to be shot with only one spear, lord, he would
  experience pain & distress from that cause, to say nothing of three
  hundred spears.
In the same way, I tell you, monks, is the nutriment of consciousness
  to be regarded. When the nutriment of consciousness is comprehended,
  name & form are comprehended. When mind & body are comprehended, I
  tell you, there is nothing further for a disciple of the noble ones to
  do.
SN 12.63

Thus, when the Buddha taught about the arising (samudhaya) of consciousness, he only taught how consciousness arises when internal defilements (asava) & thoughts (sankhara) that lead to suffering condition (paccaya) consciousness to arise, as follows:

With the arising of formations (sankhara) there is the arising of consciousness.
  With the cessation of formations there is the cessation of
  consciousness. The way leading to the cessation of consciousness is
  just this Noble Eightfold Path; that is, right view... right
  concentration.
MN 9

Thus, it terms of actually causality (hetu), all the Buddha taught was the manifestation or knowing (paññāpanāyā) of consciousness is caused (hetu) by the mind & body (nama-rupa), as follows:

Nāmarūpaṃ hetu, nāmarūpaṃ paccayo viññāṇakkhandhassa
  paññāpanāyā.
Nama-and-rupa is the cause and condition for the manifestation of the
  consciousness aggregate.
SN 22.82

The above quote from SN 22.82 refutes the non-Buddhist idea below because the physical body (rupa) is said to be one of the causes (hetu) of consciousness:

The strongest reasoning I've seen other... give for literal
  rebirth is that each instance of consciousness must have a substantial
  cause. And that brain/matter cannot be that substantial cause because
  brain and consciousness are fundamentally of two different natures.

The Buddha used the term 'nama-rupa' ('mind-body') has a compound thus did not quibble about whether mentality has an exclusive mental origin, as follows:

Feeling, perception, volition, contact and attention — these are
  called mentality. The four great elements and the material form
  derived from the four great elements — these are called materiality.
  So this mentality and this materiality are what is called
  mentality-materiality.
MN 9

What the Buddha primarily taught about consciousness is consciousness arises dependent upon physical & mental sense organs and physical & metal sense objects as its condition, as follows:

Dependent on eye & forms, eye-consciousness arises....
Dependent on ear & sounds, ear-consciousness arises...
Dependent on nose & aromas, nose-consciousness arises...
Dependent on tongue & flavors, tongue-consciousness arises...
Dependent on body & tactile sensations, body-consciousness arises...
Dependent on intellect & ideas, intellect-consciousness arises.
MN 18

Therefore, the Buddha never taught the idea: "that brain/matter cannot be a substantial cause of consciousness because brain and consciousness are fundamentally of two different natures".

So #3 and because the Buddha said so?

Can you use reasoning to arrive at the answer? If so, can you explain your reasoning?

I provided an answer to your question from the reported teachings of the Buddha. This is the only answer the Buddha can provide. However, later philosophers may provide some speculations. Regards


text:
How do Buddhists reconcile "Anatta" with Buddha supporting the existence of the Self in the Mahayana Mahaparininirvana Sutra?
In the third chapter of the Mahayana Mahaparininirvana Sutra, Buddha calls the Self real and permanent:

Then the Buddha said to all the bhiksus: "Do not say this. I now leave all the unsurpassed Dharma in the hands of Mahakasyapa. This Kasyapa will henceforth be the one upon whom you may rely. This is as in the case where the Tathagata becomes the one to whom all beings can turn. The same is the case with Mahakasyapa. He will now become your refuge. This is as in the case of a king who has many territories and who goes on a tour of inspection, leaving all affairs of state in the hands of his minister. The same with the Tathagata. All right teachings are left in the hands of Mahakasyapa. Know that all that you have learned up to now about the non-eternal and suffering is not true. In spring, for example, people go bathing in a big pond. They are enjoying themselves, sailing in a boat, when they drop a gem of beryl into the depths of the water, after which it can no longer be seen. Then they all get into the water and search for this gem. They competitively scoop up all such rubbish as tiles, stones, bits of wood, and gravel, and say that they have the beryl. They are glad and take the things out, and see that what they hold in their hands is not true. The gem is still in the water. By the power of the gem itself, the water becomes clear and transparent. As a result, the people see that the gemis still in the water, as clearly as when they look up and see the form of the moon in the sky. At that time, there is a wise man there who, working out a power, slowly gets into the water and gains the gem. O you Bhiksus! Do not abide in the thought of the non-Eternal, Suffering, non-Self, and the not-Pure and be in the situation of those people who take stones, bits of wood, and gravel to be the true gem. You must study well the Way, how to act, wherever you go, and “meditate on the Self, the Eternal, Bliss, and thePure”. Know that the outer forms of the four items which you have learnt up to now are inversions and that anyone who desires to practise the Way should act like the wise man who deftly gets hold of thegem. This refers to the so-called thought of Self, and that of the Eternal, Bliss, and Pure."

Now, as far, as I know, Buddhists believe in the concept of "Anatta" i.e. No-Self which seems to contradict the above passage. So how Buddhists reconcile the third chapter of the Mahayana Mahaparinirvana Sutra with the concept of "Anatta"?

How is this a duplicate? That question was about what Buddha said. This one is how Buddhists intepret it. @ChrisW

You're saying that "What the Buddha said" and "How Buddhists interpret it" aren't the same question? I thought that the answer[s] to the other question were also an answer to this one (i.e. that this question is already answered by the answers to the other question).

@ChrisW I don't see any satisfying answers there.

I hope you find a better answer here, then. One of the answers there was edited, I don't know why, I thought the previous version was better -- see the older version of the answer here.

Where is the link to the quotation?

@DheerajVerma I added a hyperlink

I am not an expert on Mahayana Buddhism, but I will try to answer this question.
I found another translation here.
For the same section quoted by OP, this other translation states:

Bhikṣus, thus you should not cultivate your ideas of impermanence,
  suffering, nonself, impurity, and so forth as if they were the true
  meaning [of the human condition]. Just like those people who took
  rocks, vegetation, or gravel to be the jeweled necklace they were
  looking for, you must carefully learn about expedient means so that
  wherever you are, you can continually cultivate your perception of
  self as well as your perceptions of permanence, bliss, and purity.

Later on, the text says:

And out of my desire to subdue the non-Buddhist paths I therefore
  declared: “There is no self,there is no person or [individual] living
  being, life span, personality, observer, actor, or experiencer.”
  Monks, the heterodox paths affirm a “self” in the same manner as [some
  infer literacy in] the shapes of letters incised into wood
  accidentally by insects. This is why the Tathāgata proclaims “nonself”
  as part of his buddha-dharma. It is because I need to straighten out
  [the thinking] of living beings—because I am aware of their
  situation—that I expound the absence of self. ....
  But what I am speaking of is not what ordinary people imagine the self
  to be. Ordinary people or ignorant people suppose the self to be the
  size of a thumb, or perhaps a mustard seed, or a speck of dust. What
  the Tathāgata explains the self to be is nothing like that. Therefore
  when I preach “dharmas are without self,” in truth they are not
  without self. So what is this self [of which I now speak]? If a dharma
  is true, real, permanent, autonomous, a basis, and its nature is
  immutable, then that is what I call self.

The term "dharma" above means "thing". So "self" is a thing which is true, real, permanent, autonomous, a basis and is immutable.
Then it continues:

[Kāśyapa continued:] “World-Honored One, is there a self or not in any
  of the twenty-five forms of existence?”
The Buddha said: Good man, “self” is precisely what tathāgatagarbha
  means. All living beings have buddha-nature, and this is what is meant
  by this notion of self. However, the significance of “self” understood
  in this way has been continuously covered over by an uncountable
  number of the defilements since the beginning [of any given
  individual’s existence], and that is why living beings have been
  unable to perceive it.

So, the "self" in the Mahayana Mahaparinirvana Sutra refers to the tathagatha-garbha or Buddha-nature.
It must be noted that tathagatha-garbha or Buddha-nature is not the same as the concept of Atman in Hinduism, as can be seen by the following excerpt from the same text Mahayana Mahaparinirvana Sutra:

Good man, if people have never heard of the profound, hidden tathā-
  gata treasury, how could they be aware of the existence of
  buddha-nature? What is it that I am calling “a hidden treasury”? I am
  talking about the well-balanced Mahāyāna scriptures themselves. Good
  man, there are other paths: some expound a self that is permanent,
  some expound a self that is cut off permanently [at death]. The
  Tathāgata is not like them. In affirming both self and nonself, I call
  it “the middle path.” One way of explaining this is that the Buddha
  expounds a middle path in which all living beings possess
  buddha-nature, but because it is obscured by the defilements they do
  not understand it and do not see it. Therefore you must diligently
  cultivate whatever expedient means you can in order to destroy those
  defilements.

According to this article:

Tathagatagarbha, or Tathagata-garbha, means "womb" (garbha) of Buddha
  (Tathagata). This refers to a Mahayana Buddhist doctrine that Buddha
  Nature is within all beings. Because this is so, all beings may
  realize enlightenment. Tathagatagarbha often is described as a seed,
  embryo or potentiality within each individual to be developed.

And it discusses further:

In the religions of the Buddha's day that were the forerunners of
  today's Hinduism, one of the central beliefs as (and is) the doctrine
  of atman. Atman means "breath" or "spirit," and it refers to a soul or
  individual essence of self. Another is the teaching of Brahman, which
  is understood as something like the absolute reality or the ground of
  being. In the several traditions of Hinduism, the precise relationship
  of atman to Brahman varies, but they could be understood as the small,
  individual self and the big, universal self.
However, the Buddha specifically rejected this teaching. The doctrine
  of anatman, which he articulated many times, is a direct refutation of
  atman.
Through the centuries many have accused the Tathagatagarbha doctrine
  of being an attempt to sneak an atman back into Buddhism by another
  name.
In this case, the potentiality or Buddha-seed within each being is
  compared to atman, and Buddha Nature -- which is sometimes identified
  with the dharmakaya -- is compared to Brahman.
You can find many Buddhist teachers speaking of small mind and big
  mind, or small self and big self. What they mean may not be exactly
  like the atman and Brahman of Vedanta, but it's common for people to
  understand them that way. Understanding Tathagatagarbha this way,
  however, would violate basic Buddhist teaching.

Another article here tries to point the origins of tathagatha-garbha or Buddha-nature to the Luminous Mind in the Pali Canon (which according to Theravada Buddhism, is not permanent or eternal, but is dependently arising - see this answer):

The term "'tathagatagarbha'" is generally taken as to mean that the
  "garbha" (womb or potential) of a 'Tathagata' exists in all sentient beings without
  exception, and though temporarily contaminated by adventitious
  defilement ('agantukaklesa'), it is the cause which eventually leads
  sentient beings to enlightenment. The notion of the 'tathagatagarbha'
  can be traced to a luminous¡A inherently pure mind (pabhassar citta)
  found in the 'Anguttara-nikaya' (1:5):
Oh! 'Bhiksus'. The mind is pure! It is defiled by the adventitious
  defilement. Oh! 'Bhiksus'. The mind is pure! it obtains liberation
  through the adventitious defilement.
When the original pure mind came to be regarded as something capable
  of growing into Buddhahood, there was the 'tathagatagarbha' doctrine.
  Although the concept of an intrinsically pure mind exists in the
  Nikaya Buddhism, many Buddhologists, such as Wayman (1), Paul (2),
  Yin-shun (3) think that the 'tathagatagarbha' thought was originated
  from the 'Mahasamgika', but was rejected by the 'Theravada'. This
  theory is also held by Mizuno who points out that the pure mind
  ('pabhassarcitta') articulated in the Nikaya Buddhism is not totally
  identical with the original pure mind ('prakrtivisuddhi-citta')
  articulated in the 'Tathagatagarbha' doctrine, for Mizuno asserts that
  the former is static whereas the latter is dynamic in that it is
  capable of eradicating defilement.(4) At any rate, the relationship
  between pure mind and the adventitious defilement appears to have been
  wholly adopted by the 'Mahasamghika' and later by the 'Mahayana'.

It also comments in its conclusion:

In conclusion, when we try to interpret the thought of the
  'tathagatagarbha', we should keep several points in mind:
1) The 'tathagatagarbha' symbolizes the potential for enlightenment (a
  principle) rather than a material "essence" of ultimate truth,
2) the 'tathagatagarbha' is based on the framework of the 'Mahayana'
  doctrine of 'sunyata-pratitya-samutpada'.
3) The development of the 'tathagatagarbha' doctrine signifies the
  ability of a religious tradition to meet the spiritual needs of the
  masses aiming at a given time.
That is to say the 'tathagatagarbha' thought was formed as an positive
  soterio-logical approach to counteract the "'sunyam sarvam'" (all is
  empty) view. The 'tathagatagarbha' which strongly articulates a
  devotional and experiential approach to salvation provides much to the
  hope and aspiration of the people at large. It is this positive aspect
  that was taken up and strongly emphasized in Chinese Buddhism.
4) The 'tathagatagarbha' doctrine is employed as a skill-in-means
  ('upaya'). This does not necessarily mean that the theory of the
  'tathagatagarbha' is neyartha, a teaching requiring further
  qualifications -- rather, it is a skill-in-means in that it is taught
  to suit the needs of a certain kind of people and circumstances. This
  is why it is said in the 'sutra' that in order to teach the emptiness
  of all dharmas, the Buddhas preach sometimes by the doctrine of the
  'tathagatagarbha', and sometimes by that of emptiness. Thus it is
  better to take the 'tathagatagarbha / Buddha nature' as representing
  "profound existence" derived from "true emptiness" rather than as a
  monistic self.

The following is the answer I believe that my tradition gives. In other words, this answer is from the perspective of the Gelug tradition of Prasangika-Madhyamaka as founded by Je Tsongkhapa as I understand it. I may be wrong :)
The Mahāyāna Mahāparinirvāṇa Sūtra is a Tathāgatagarbha Sutra and thus belongs to the Third Turning of the Wheel of Dharma. Je Tsongkhapa lays out in the lam rim how the Sutras from the three turnings should be interpreted. The first turning Sutras are said to be provisional in meaning. The second turning Sutras are said to be definitive in meaning. The third turning Sutras are said to have been given to allay the fears of those who have heard the second turning Sutras and adopted a view of nihilism: that the Prajnaparamita Sutras essentially mean that nothing exists and that karma does not exist, etc, etc.
In other words, the Buddha gave the teachings of the Third Turning of the Wheel of Dharma as a skillful means to stop some individuals who had heard the Second Turning teachings and understanding them incorrectly were going down the road to nihilism and thus the avici hell. Thus the Third Turning teachings have an essentialist sheen in order to arrest the nihilist tendency in these individuals.
That is how I have understood it at least. If you wish me to or you think it would be helpful I can provide quotes from the relevant works of Chandrakirti, Je Tsongkhapa and other prominent teachers from the Gelug branch of Prasangika-Madhyamaka. For now, here is the wikipedia page ;)

In the Tibetan tradition, the Gelug school considers the second turning definitive, as do some scholars in other schools.

I hope and believe this answer might be useful for sentient beings.

Namo Buddhaya. I will give a logical answer. Logically there is no self(no self which is permanent, unchanging and blissful). I am different from what I was 10 years ago and I will be different from what I am today. However my past is connected with the present and the present is connected with the future through Karma. It is like, I started off as milk then I became curd then I became Ghee and so on... I am different in many ways and similar in many ways with the past. But there is no permanent identity which can be called as ME. And there is no unchanging identify which can be called as ME. The sense of Self which gets generated is due to craving. Craving for the five aggregates.If you stop clinging to the five aggregates the sense of self will disappear and also will the suffering. The self which you think exists is nothing more than illusion. The reality is that there is nothing worth clinging to in terms of form, feelings ,perceptions, consciousness and volitional formations because they are not permanent, unchanging and blissful.
This fact remains undisputed whether Buddha arises or not. Whether you are a Buddhist or not. Anatta remains true. In my opinion we need to support the long story from  Mahayana Mahaparinirvana Sutra with more examples. Buddha would have explained that in many other ways as he was Great Teacher.

From the Tibetan Gelug viewpoint, the perfection of self posited in the Nirvana Sutra is not what you would translate as 'atman'. Therefore, there is no contradiction.
The self that is asserted in the Nirvana Sutra has nothing to do with the atman that we negate.
As it says in Gyaltsab Je's commentary to Maitreya/Asanga's Sublime Continuum:

The perfection of the highest self refers to the final nature, the
  emptiness of the self, that is, the emptiness of true existence of the
  self.

And:

The highest self or holy self refers to selflessness or no-self, as
  translated here, which is the result of the development of the
  perfection of wisdom

In addition, the perfection of permanence in this context does not refer to the entity of permanence, but to the deeds of a buddha being uninterrupted.

I think this answer is in accord with my answer in that this sutra when interpreted with the viewpoint of emptiness leads to no contradiction.

I think so too. However, you didn't specify what we understand this self to be. Here, what I mean is not so much "Buddha taught a self to people afraid of no-self" but rather "This self Buddha speaks of is not the self that you think of and that Buddha indeed negated. In fact it's called self but it has nothing to do with self."

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text:
What are the Three Turnings of the Wheel of Dharma according to Tibetan Buddhism?
Tibetan Buddhists often talk about the Three Turnings of the Wheel of Dharma...
What are the Three Turnings of the Wheel of Dharma according to Tibetan Buddhism?
Where did they take place according to Tibetan Buddhists?
How do Tibetan Buddhists interpret these Three Turnings?
Is there disagreement within Tibetan Buddhists schools about which teachings are definitive and which are provisional?
Do Tibetan Buddhists think these Three Turnings are contradictory?

According to Prasangika, or Svatantrika?

I attempted in my answer below to represent the parts where the different Tibetan subschools agree and where they disagree. Please let me know if I made any errors!

FWIW, I just learned that posting a question+answer on this site is frowned upon. This was motivated by a specific request, but will take care when doing this again.

@TenzinDorje if i wanted to contact you over email would I send an email to Kopan Monastery or Nalanda?

That would be Nalanda. But you can simply write at tenzin.dorje.pt@gmail.com

What are the Three Turnings of the Wheel of Dharma according to Tibetan Buddhism?
Where did they take place according to Tibetan Buddhists?
The Three Turnings of the Wheel of Dharma according to Tibetan Buddhists are broadly speaking three different categories of teachings the historical Buddha gave as recorded in various Sutras.
The First Turning of the Wheel of Dharma is said to have been given at Deer Park in northern India. Here is an article cited by the FPMT which describes what Tibetan Buddhists believe constitute this first turning:

The first turning includes those teachings given by the Buddha in the
  earliest historical period of Buddhism in general, and Buddha
  Shakyamuni’s teaching career in particular.  Many of these teachings
  are fundamental to all schools of Buddhism such as the four noble
  truths, the eightfold path, selflessness (anatman), dependent-arising,
  impermanence, the five aggregates, etc. Perhaps the most famous of the
  many discourses (Pali: sutta, Sanskrit: sutra) of the Buddha from the
  first turning is the one that records the Buddha’s very first teaching
  at Deer Park to the first five disciples entitled The Turning of the
  Wheel of the Dhamma Sutta. In actuality, virtually all of the contents
  of the Pali version of the Buddhist canon, that version utilized by
  Theravada Buddhists of Sri Lanka and Southeast Asia today, are
  considered by Tibetans to be teachings from the first turning of the
  wheel.

The Second Turning of the Wheel of Dharma is said to have been given at Vulture Peak Mountain in Rajagriha, India. The Sutras which record this turning are broadly given the title of Perfection of Wisdom Sutras or prajnaparamita the most famous of which are likely the Heart Sutra and the Diamond Cutter Sutra.
The Third Turning of the Wheel of Dharma is said to have been given in numerous locations and generally comprise those Sutras making up what is called the Tathāgatagarbha doctrine.
How do Tibetan Buddhists interpret these Three Turnings?
Is there disagreement within Tibetan Buddhists schools about which teachings are definitive and which are provisional?
Among the various subschools of Tibetan Buddhism there is broad agreement about these Three Turnings. In other words, the subschools generally agree that these are valid and authentic teachings of the Buddha. However, there are some disagreements.
I'm not aware of any disagreements about the First Turning which are widely considered provisional in meaning, but there is some contention about the status of the Second and Third and which Sutras are said to be definitive in meaning and which are provisional.
The Gelug school as founded by Je Tsongkhapa and which forms the root lineage of His Holiness the Dalai Lama believe the Second Turning to be definitive in meaning while the Third is said to be provisional or at least that it needs to be interpreted with the wisdom realizing emptiness. According to the Gelug viewpoint the Third Turning was motivated to dispel the fear that some generated upon hearing the teachings of the Second Turning. That is, some listeners had an incorrect understanding of the Second Turning and developed a nihilistic view and so out of compassion the Buddha gave the Third Turning with a sheen of essentialism to dispel this nihilism which leads to the avici hell.
Tsongkhapa gave his viewpoint in his Essence of True Eloquence.
Here is what His Holiness the Dalai Lama has to say about this:

"At a time when Tsongkhapa's work ‘Essence of Good Explanation’ on the
  provisional and definitive meaning of the Sutras was translated into
  Hindi at Varanasi, the pandits Tripathi and Upadhyaya were involved. I
  asked Tripathi to consider Je Rinpoche's work in the context of the
  great Indian classics and wondered whether he might be classed among
  the scholars of Nalanda. Tripathi responded that he would not only
  hold his own among them, but would be classed among the most
  excellent."

It is important to understand that the Second and Third Turning teachings predate Tibetan Buddhism. These teachings were recorded and came from India before Buddhism was ever introduced to the land of snow. However, the Second and Third Turnings were not recorded in the Pali Canon and thus properly belong to the Mahayana.
Do Tibetan Buddhists think these Three Turnings are contradictory?
No.
There is very wide agreement that these teachings - when interpreted correctly and with a proper view of which are provisional and which are definitive - do not contradict each other.

So, do you think Buddha was talking about eternal subjective self?

Hi Rohith, I'm not sure what is meant by "eternal subjective self"? To first reading, I'd say that "eternal" and "subjective" seem in some conflict to each other.

My own viewpoint is that Prasangika-Madhyamaka is the most subtle and correct view of the wisdom realizing emptiness as explained by Buddha -> Nagarjuna -> Aryadeva -> Buddhapalita -> ChandraKirti - Je Tsongkhapa however, it is very difficult even to get an inferential understanding of emptiness.
That is, I think all phenomena lack inherent existence including nirvana, samsara, and emptiness itself. There is no existent whatsoever that has inherent existence even the slightest bit. That is every existent is completely and thoroughly dependent. And truly realizing this can give liberation.

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text:
Did Dignaga argue against real relations?
Did Dignaga argue against real relations? I gather that his student, Dharmakirti, did.
I'm asking only because I'd disagree, but am skeptical about universals.

On what basis do you, "gather that his student, Dharmakirti" argued against real relations? I'm just looking for the sources that you are using to inform the context...

i don't have the book to hand, sorry @YesheTenley

DharmaKirti and Dignaga are highly revered in Tibetan Buddhism and their work is used as foundational materials in Tibetan Buddhist monasteries to this day including the famous Sera Jey Monastery. However, they are also considered to have espoused or based their work on either the Yogachara tenet system, the Sautrantika tenet system or some combination thereof.
In brief, Yogachara/Chittamatra is a tenet system of the Madhyamaka and the Mahayana which believes in the selflessness of persons and selflessness of phenomena, but also believes in true existence which is refuted by the Prasangika-Madhyamaka. The Sautrantikas in general did not posit the selflessness of phenomena and are a tenet system strictly associated with the Fundamental Vehicle (like modern Theravada) as opposed to the Mahayana.
So if by "real relations" you mean "true existence", then I think both Dignaga and Dharmakirti posited real relations. If by "real relations" you mean "inherent existence", then I think both refuted real relations.
However, perhaps it is best if you elucidate what you mean by real relations and/or universals otherwise it is very easy in my experience to misunderstand one another. In my experience, when discussing tenet systems precision of language is key and knowing the jargon is very important even if difficult. I'm still struggling with it :)

by relations i just mean the standard dictionary definition. e.g. being taller than. 'universals' is a more obscure term, but for the sake of argument we can mean everything except particulars and relations

I think it is important to understand the Yogachara/Chittamatra viewpoint and especially the three natures doctrine in order to correctly categorize DharmaKirti and Dignaga's thought.
Your usage of the word "real" I think is indicative of true existence and Yogachara does posit true existence.

yes but they do say that universals aren't real

I have a feeling that this is getting to the same issue that was discussed here recently: https://buddhism.stackexchange.com/a/26061/13375
In other words, Prasangika does not accept conventional truth to be real from the perspective of an awakened mind. It only accepts conventional truths to be real from the perspective of an ordinary being... ie, conventional truths are only real conventionally ;)
Yogachara on the other hand does not posit such a distinction. For them, conventional truths are real from the perspective of an awakened mind.

i'm not sure, maybe i'm being unclear about what 'universal' means

If my hypothesis above is correct, then from Yogachara perspective (ie, Dignaga and Dharmakirti perspective), "universal" would refer to real things from the perspective of the ultimate. ie, a universal would be an inherently existent thing.
This is the way that Yogachara posits emptiness via two truths.

From the ultimate perspective nothing is real -> everything is empty -> nothing has inherent existence -> ultimate truth
From the ordinary/conventional perspective -> there are real and unreal things -> conventional truth

Given above... the distinction about "real things" between Yogachara and Prasangika would then be answering the question, "from the ultimate perspective, are conventional truths real?" and Yogachara would answer "yes!" and Prasangika would answer "No."


text:
How important is motivation in determining the virtue/non-virtue of a karmic action?
I ask this question because I assumed the importance of motivation being paramount in determining the virtue/non-virtue of karmic action was widely shared among all traditions. Anyway, I'd like to know if this assumption is correct from practitioners of other traditions.
So how important is motivation in determining whether a particular action is virtuous or non-virtuous?
Are there any actions where motivation is not important? Are there any actions where it is the only thing that is important? Something in between?

There are two presentations:

The general presentation, and
The particular presentation.

In general, we say that a non-virtue is a non-virtue regardless of one's intentions. For instance, we say that killing is a non-virtue regardless of one's motivation, regardless of consequences, etc. This is why, in the great and middle-length Lam rims, Je Tsongkhapa simply explains how important the motivation is in determining, not whether an action is virtuous, but whether an action is heavy.
However, the general presentation does not stand in debate. Therefore, by digging a little, you find presentations that contradict the general statement.
The Lam rim gives the general presentation. It says that there are two types of non-virtue:

Deeds wrong by nature, or 'natural misdeeds' (rang bzhin gyi kha na ma tho ba)
Deeds wrong by prohibition, or 'proscribed misdeeds' (bcas pa'i kha na ma tho ba)

An example of natural misdeed is killing. An example of proscribed misdeed is for a monk to eat after mid-day.
According to the Lam rim, a natural misdeed is a non-virtue regardless of perception, attitude, affliction, and conclusion. However, a non-virtue can be more or less heavy, depending on (1) perception, (2) attitude, (3) affliction, and (4) conclusion. For instance, Killing unintentionally... or under duress... is not as heavy as killing willingly, intentionally. However, in any case it is a non-virtue. Here, with respect to perception, Je Tsongkhapa says:

In some cases, there may be a specific motivation. For example,
  someone may plan to kill only someone called Devadatta, and he or she
  then commits murder. However, if this person mistakes Yajnadatta for
  Devadatta and kills him instead, there is no [completeplete infraction
  with all its aspects fullfilled.]

This is the general presentation. It is given in the context of practices common with beings of small capacities. In the context of bodhisattva practices, however, things are different.
In the Book of Kadam, Atisha says:

As for someone like you, Drom, who has secured a firm ground, who does
  not even care to take birth in cyclic existence, who focuses
  exclusively on other’s welfare, you can engage in the seven nonvirtues
  by relating them to [the application of] skillful means. Those are
  [only] similitudes of nonvirtue.

And in the footnote, it says:

Here the text is alluding to an important aspect of the bodhisattva
  ethics, according to which highly evolved bodhisattvas can creatively
  engage in the seven nonvirtuous actions—the three bodily acts of
  killing, stealing, and sexual misconduct and the four verbal deeds of
  telling lies, divisive speech, harsh speech, and frivolous speech— on
  the basis of the principle of skillful means. In fact, if the
  situation demands a deliberate violation of the ethics of restraint
  from any of these seven nonvirtuous acts, such as when the well-being
  of a large number of other sentient beings is involved, refraining
  from the act is actually a transgression of the bodhisattvas vows. For
  a detailed discussion of this important aspect o f the bodhisattva
  ethics, especially with reference to their key scriptural sources in
  the Mahayana sutras, see Mark Tatz s Asangds Chapter on Ethics with
  the Commentary ofTsong-Kha-Pa, pp. 211-17.

The meaning is that a non-virtue conjoined with the wisdom of emptiness and bodhicitta is a similitude of non-virtue. It looks like a non-virtuous actions but it is not. One has to keep in mind that such do not occur prior to the Mahayana path of seeing. A non-virtue in the continuum of anyone but a bodhisattva on any of the ten grounds is a non-virtue regardless of one's intention.
See the topic: How does upaya (skillful means) feature in Tibetan Buddhism?

I know I have acted in ways that were bourne of nothing but good intent, yet caused great suffering in those close to me.
I do not feel guilty about that, but I do feel sad. Intent is crucial, but ignorance can live underneath, leading us to act in ways that seem reasonable, but actually cause harm.
In the end, what is it you want? Do you want to look after your own karmic legacy, or do you want to reduce the suffering of those around you?
If the latter, then intent is very important, but the actual consequences matter too.
There was a case where the Buddha taught an insight practice to some monks. He came back a few days later and they had committed suicide. He undoubtedly learned from this! So, in terms of consequences, none of us are immune from 'unexpected' ones. Yet we can continue to learn, and find ways to increase the effectiveness of our actions in bringing about increased wellbeing in those around us.

Intention is indeed the most important element of karma.
From Dhammapada 1:

On one occasion, Thera Cakkhupala came to pay homage to the Buddha at
  the Jetavana monastery. One night, while pacing up and down in
  meditation, the thera accidentally stepped on some insects. In the
  morning, some bhikkhus visiting the thera found the dead insects. They
  thought ill of the thera and reported the matter to the Buddha. The
  Buddha asked them whether they had seen the thera killing the insects.
  When they answered in the negative, the Buddha said, "Just as you had
  not seen him killing, so also he had not seen those living insects.
  Besides, as the thera had already attained arahatship he could have
  no intention of killing and so was quite innocent." On being asked
  why Cakkhupala was blind although he was an arahat, the Buddha told
  the following story:
Cakkhupala was a physician in one of his past existences. Once, he had
  deliberately made a woman patient blind. That woman had promised him
  to become his slave, together with her children, if her eyes were
  completely cured. Fearing that she and her children would have to
  become slaves, she lied to the physician. She told him that her eyes
  were getting worse when, in fact, they were perfectly cured. The
  physician knew she was deceiving him, so in revenge, he gave her
  another ointment, which made her totally blind. As a result of this
  evil deed the physician lost his eyesight many times in his later
  existences.
Then the Buddha spoke in verse as follows:
  Verse 1: All mental
  phenomena have mind as their forerunner; they have mind as their
  chief; they are mind-made. If one speaks or acts with an evil mind,
  'dukkha' follows him just as the wheel follows the hoofprint of the ox
  that draws the cart.

Also showing the importance of intention is Dhammapada 124:

At Rajagaha there was once a rich man's daughter who had attained
  Sotapatti Fruition as a young girl. One day, Kukkutamitta, a hunter,
  came into town in a cart to sell venison. Seeing Kukkutamitta the
  hunter, the rich young lady fell in love with him immediately; she
  followed him, married him and lived with him in a small village. As a
  result of that marriage, seven sons were born to them and in course of
  time, all the sons got married. One day, the Buddha surveyed the world
  early in the morning with his supernormal power and found that the
  hunter, his seven sons and their wives were due for attainment of
  Sotapatti Fruition. So, the Buddha went to the place where the hunter
  had set his trap in the forest. He put his footprint close to the trap
  and seated himself under the shade of a bush, not far from the trap.
When the hunter came, he saw no animal in the trap; he saw the
  footprint and surmised that someone must have come before him and let
  cut the animal. So, when he saw the Buddha under the shade of the
  bush, he took him for the man who had freed the animal from his trap
  and flew into a rage. He took out his bow and arrow to shoot at the
  Buddha, but as he drew his bow, he became immobilized and remained
  fixed in that position like a statue. His sons followed and found
  their father; they also saw the Buddha at some distance and thought he
  must be the enemy of their father. All of them took out their bows and
  arrows to shoot at the Buddha, but they also became immobilized and
  remained fixed in their respective postures. When the hunter and his
  sons failed to return, the hunter's wife followed them into the
  forest, with her seven daughters-in-law. Seeing her husband and all
  her sons with their arrows aimed at the Buddha, she raised both her
  hands and shout: "Do not kill my father."
When her husband heard her words, he thought, "This must be my
  father-in-law", and her sons thought, "This must be our grandfather";
  and thoughts of loving-kindness came into them. Then the lady said to
  them, ''Put away your bows and arrows and pay obeisance to my father".
  The Buddha realized that, by this time, the minds of the hunter and
  his son; had softened and so he willed that they should be able to
  move and to put away their bows and arrows. After putting away their
  bows and arrows, they paid obeisance to the Buddha and the Buddha
  expounded the Dhamma to them. In the end, the hunter, his seven sons
  and seven daughters-in-law, all fifteen of them, attained Sotapatti
  Fruition.
Then the Buddha returned to the monastery and told Thera Ananda and
  other bhikkhus about the hunter Kukkutamitta and his family attaining
  Sotapatti Fruition in the early part of the morning. The bhikkhus then
  asked the Buddha, "Venerable Sir, is the wife of the hunter who is a
  sotapanna, also not guilty of taking life, if she has been getting
  things like nets, bows and arrows for her husband when he goes out
  hunting?" To this question the Buddha answered, "Bhikkhus, the
  sotapannas do not kill, they do not wish others to get killed. The
  wife of the hunter was only obeying her husband in getting things for
  him. Just as the hand that has no wound is not affected by poison, so
  also, because she has no intention to do evil she is not doing any
  evil."
Then the Buddha spoke in verse as follows:
  Verse 124: If there is no
  wound on the hand, one may handle poison; poison does not affect one
  who has no wound; there can be no evil for one who has no evil
  intention.

Are you speaking from point of view of Theravada? Does Theravada accept that killing a sentient being with a completely pure and perfect intention is a similitude of non-virtue?

@YesheTenley Yes, that's Theravada. No, Theravada doesn't accept intentionally killing a being (see also Can Buddhism give any justification for military violence?). In the first story, Thera Cakkhupala was blind and had no intention at all of killing, and he stepped on them accidentally. And in the second story, the wife herself wasn't killing at all (Theravada does allow people to e.g. buy meat as long as they don't ask someone to kill the animal for their sake).