I have heard it said, or at least implied, that reason is tautological. And this most often, in my experience, by those espousing the “efficacy” and “truth” of eastern philosophy (mysticism), which they present as a counter-means of interpreting reality to that of western “logic”. What they mean by this–that is, reason’s tautology–is that reason is reason simply because it is reasonable. That is, it is defined by merely naming itself. Like, when you ask why God is good, and someone answers by saying “because He is God”. This is, at first glance, fundamentally a non-answer. Because the “answer” simply circles back to the assertion. The assertion then has no proof because it is unsupported by an exposition wherein it conforms to a set of criteria, defined according to a specific context, so that its efficacy can be demonstrated, even if it be done so conceptually. In which case the assertion is not an assertion at all because it cannot be applied to anything, practically speaking, outside of itself. So it’s just…nonsense. It’s nothing. It’s void. Irrelevance.
Of course we must be careful when making accusations of tautology. Because what may seem tautological on the surface (like reason, or God’s goodness) may not actually be so. A good way to vet this claim of a thing being labeled a tautology can be to ask a different question…one that had you answered it first, would have nullified any point of the first question.
For example, if we ask “Why is God good?”, and the answer is “Because He is God”…well, instead of immediately calling tautology you may want to ask “Who or what is God?”. And the answer to this question may answer the other. That is, if we can properly define God then we will also know precisely why He is good.
The same, I submit, is true for reason. If we have a definition of reason–a definition that makes sense, not according to reason but according to the concept “definition”–what qualifies as “being defined”–then we will know precisely why reason is itself reasonable. The apparent tautology is resolved. I have found that this tactic is a great way to separate the true tautologies from the merely presumptive ones.
Here is a true tautology.
Man is totally depraved–total depravity being the common Christian (most popularly Protestant) metaphysic. And see, this is key. Total depravity is not merely one characteristic among many of human beings. It is humanity. It is man’s irreducible ontological state. So the answer to the question “Why is man totally depraved?”, is “Because he is man”. And thus you shall then ask, “Okay. So what is man?”. And the answer, because depravity is indeed a metaphysical assertion according to the doctrine, is “Man IS depravity“.
And this, my friends, is what a true tautology looks like. Man is depraved because he is depravity. What is man? Depravity. What is depravity? Depravity is man. Both concepts are thus destroyed because they infinitely circle back upon themselves. They have no relevance to reality whatsoever because they cannot be defined; they cannot be contextualize. They are made “distinct” and yet no distinction is able to be provided. This wrecks them both. And thus the assertion that man is depraved becomes a logical fallacy.
Reason, on the other hand, is a false tautology.
Why is reason reasonable?
Because it’s reason.
What is reason?
Ah…good question. Reason is conceptual consistency. It is the combination of any given number of abstract (like “left” or “happiness”) and/or material (like “tree” or “Joey Ramone”) concepts in a way in which the concepts do not contradict themselves (e.g. “Joey Ramone took a right at the corner, which was in a leftward direction.”) in order to convey an idea to one who shares your existential frame of reference (that is, another conscious/moral agent).
And this is the real answer to the question “Why is reason reasonable?”. The real answer is: because it doesn’t contradict its own definition. Nor, I would add, is anyone who affirms the validity of reason suggesting, as far as I can tell, that it is its own definition. Reason, defined, is not “reason”, and I know of no one who has suggested such a thing aside from the mystics who (falsely) claim that it’s tautological. Reason is conceptual consistency. It is the integration of ideas which do not self-nullify.
“Reason”, then, is simply the term given to why communication between moral and conscious agents is actually possible.
unreformingtheology 
Thank you I like that. I was almost going to ask the question of whether or not reason occurs or exists outside the spoken word, but then you neatly close that gap in your last sentence.
Yeah I have to wonder a little bit what’s really going on with your statement your short essay here.
Because my question would indeed be is there reason somehow beyond or separate from the spoken and communicated word? Or is what is communicated or located within the attempt to communicate, folded back into consciousness such that there is a thinking that is reasonable or that can be called reason that necessarily extends in both directions at once, which is to say in the already potentiated word of communication?
Perhaps this is where the as you say eastern people want to say reason is a tautology. But then I would move to say they are probably the most mistaken or they evidence a larger mistake then the purely ‘logic reason’ side. But that there is some sort of confusion going on between the designation of those two sides.