I think I'm actually using the word "sentience" too broadly... "consciousness" seems a better term. I hope my meaning was at least clear. I don't want to discount self-awareness, which the word "sentience" alone can.

Can you provide physical evidence of reason?

From how I understand it (and I might be wrong). Todangst sure ly could give you the answer you are looking for. Physical evidence of reason is in the firing pattern of synapses in the brain. The brain is responsible for reason, but it is a sum of it's parts, there is not one single neuron responsible for any one function.

Cpt_pineapple (not an atheist) already alluded to the answer, but I think the best response is "I think therefore I am". The fact that we do reason proves that reason occurs.

First, I think we are talking about two different ideas when you talk about the existence of reason and the existence of God. God, although slightly abstract would have to exist in order to be able to create, judge, forgive, and do all the things he supposedly does. Reason, on the other hand, is a man made abstraction that is not directly observable, so to speak.

However, we can test it scientifically by setting up a set of criteria and infer if an indivdiual is reasonable or not. In fact, the majority of the social sciences are based on this idea. For instance we don't know what intelligence looks like. We can't see it. However, we can observe it when we give somebody an objective test. The same idea goes for depression and schizophrenia. We can also see these through brain scans, which is what BGH was sort of alluding to through neuronal firing. However, we cannot observe the hallucinations that the schizophrnic is experiencing and we can't see the self-defeating thoughts and negative thinking of the person who is depressed. We infer that they have this or suffer from that based on their behaviors and self-reports, which are measured by objective tests. These tests and scientifically and statistically tested. For example, most individuals who are diagnosed with depression will score this on the test when compared to those who do not have the disorder.

All this being said. You can apply the same idea to reason. We actually call some portions of I.Q. tests, tests of reasoning ability. Although, I don't think they are measuring what you are suggesting. I do think that this is how you could obserive reason.

Yes, we certainly would be.  I'm actually trying to leave God out of this particular discussion.  I would, however, argue that reason is an abstract concept, but not man-made (apart from the language and philosophy to understand it, but that applies to anything).  I'm content to simply disagree on the need to specify a creator for this thread, if that's all right.

This is an idea I had considered a bit, but one thing troubles me.  It's reliant on second-hand information.  Outside of a formal discussion, I presume we're informed on the workings of a mind (our own) by first-hand experience.  In a strictly empirical sense though (and the thrust of my question), we have no first-hand knowledge of anyone else's mind apart from what they tell us.  We can assemble theories only on the assumption that we have accurate reports.

The conversation could be further compounded by introducing the notion of mental illness (and the necessary contrast of mental health which defines it).  How can we judge this?  I think that's beyond this discussion, since the various mental disciplines themselves don't fully agree.

This is close to compelling.  I don't mean to simply be difficult, but I must essentially "take your word for it" that reasoning took place.  You've said what seems like a reasonable conclusion, but couldn't it also be a social instinct played out in the complex communication of our species?  Both things seem like logical leaps to me.  We see the result, and have a common hypothesis of cause, but it can't really be proven.  No physical evidence can be rendered.

I somewhat said it above, but I want to be clear.  I'm not pressing this question to be difficult or to pull out some proof of God from getting someone to say they can't render evidence of the mind.  As I said before the question, I honestly expect a reasonable answer to proof of consciousness.

Obviously I think there is a God, and obviously the athiests here do not.  I have been confronted with demands of evidence, so I am hoping to better understand what qualifies as sufficient evidence.  It may be that belief in the mind is entirely inductive - I have a mind, therefore everyone has a mind, and corroborating if circumstantial evidence is sufficient proof.

Still, I want to carry out the discussion sufficiently to explore its depth, because I think it may be very deep indeed.

No need. Proofs are for deductive logic. I don't need deductive logic to demonstrate to myself that I reason: the fact that I reason is axiomatic, and defended through retortion.

If you haven't already picked up my answer from my last post, I'll be more explicit: your question is predicated on the fact that you already accept that there is evidence that others reason.

By the way, all evidence is physical - if we can't see it, touch it, feel it, hear it, smell it... how else can we 'know of it'?

Yes, you are actually.. you're just missing it.  Your comments here on the board are necessarily predicated on your acceptance of the existence of evidence of reason: our posts.

We learn about the consciousness of others through behavior.

Now, do we need to talk about philosophical zombies? May I say "ugh" first? 

It's not even necessary to prove that we, ourselves, have consciousness: it is axiomatic that we are conscious.  This is the most secure knowledge we can have, it is even more basic than deduction, is the most basic knowlege of all - a metaphysical axiom.

There is, however, a problem in philosophy called the 'problem of other minds". Yes, I know that I am conscious, that I reason, this is necessarily true by the very nature of awareness of self. But how do I know that others reason just as I do?

This usually brings up 'philosophical zombie' talk, and honestly, I'd rather go watch the copy of "dawn of the dead" that I just rented, if I'm going to be thinking of zombies tonight... 

 I'm Playing Dead Rising (Xbox 360). It's a really fun zombie game.

Dear OP, I can prove to you that your consciousness exists, though it will be an indirect proof, and it will be a proof that you will certainly NOT want to undergo yourself.

We already identify most of the elements of what you may call "consciousness" as processes of different parts of the brain. Take out that part of the brain, and that consciousness element goes away as well. See where I'm getting?

So, which part of your consciousness do you want me to demonstrate it only depends on the brain? The ability to recognize others ("Red Ribbon" Syndrome)? The ability to communicate (aphasy)? The ability to recognize and control your own body (callosal disconnection)? Or do you want to undergo a very fun experiment: take out the whole brain, let's see whether there's any "you" left ? Haunt me this tuesday at 6 o'clock GMT if you're still there.

Maybe I misunderstand the zombie argument. But my understanding of it is that it asks the reader to imagine a being -- a zombie -- who is indistinguishable from a conscious human in every way, but they're not conscious, with no qualia or perceptions. Then, it is argued, this proves that the mind cannot be material, because the zombie would be materialistically the same as a human but not conscious. But this strikes me as circular -- assuming that there's a being materially identical to humans but with no mind implicitly requires that the mind not be material. I'm sure I've got the argument wrong, because I can't imagine the circularity objection not having been noticed earlier.

The concept of 'qualia' is even more dead than philosophical zombie talk. 

I think my basic interest from the original question has been answered in the many replies since my last post.  One of two conclusions seemed necessary, and I was curious which would be reached.  Either a) evidence of minds beyond the personal one could be rendered, or b) evidence is not the only criteria for accepting knowledge.

Just to hammer home the clarity of my previous disclaimers: I'm not trying to prove God somehow with this discussion, just validating what is accepted among this community as sources for knowledge.  Hopefully, it can illuminate common ground from which we can talk.

To respond briefly to some comments made:

Yes, I think there is evidence of God, but not direct evidence.  Essentially, it would be validating proof with an existing assumption of God.  That's nothing new though, and irrelevant without that existing assumption (therefore, irrelevant to theist/athiest debate).

I don't think consciousness itself is axiomatic, although my consciousness can be (whomever the speaker may be).  We infer that others have consciousness through observing their actions (results).  Our actions, derived from consciousness, mirror those of other people.  No contradictions exist to this theory, either.  It makes the theory extremely probable, but not axiomatic.

That is, unless you mean "axiomatic" in terms of something necessarily accepted to allow for further discussion.  Certainly that's true, but historically many axioms have ultimately been refuted and proven false.  The shape of the world is a fairly classical example.  I wouldn't call that better than deduction.

Also, acceptance of consciousness as a human universal would be inductive, not deductive.  I'm not about to demand validation of inductive reasoning, though.  I consider it a necessary thought process for survival and development, whether valid or not.