Just wanted to check in (I feel bad when I don’t respond to threads I’ve started). I don’t have anything to add to the discussion, as most of these issues are beyond me. Thanks for the responses thus far, it’s been educational.
Sua
hawthorne, I am interested in a particular point of your most recent post; to wit, what is the A,B and C,D that you mention (at least one example) where If I choose one element of {A,B} then I am compelled to take a specific element of {C,D} under a rational choice?
Which is to say, you say that if A then C (for example) is a rational choice. What is that?
I think that man is almost exclusively rational, except in rare instances (notably insanity). Say that I want to lose weight. It’s really important to me that I lose weight. But I really like Twinkies, so I go buy a box of Twinkies and eat the whole thing. Am I irrational? No, I made a rational decision in which my desire to eat Twinkies overrode my desire to not be a big fat-ass. Just about every decision made by people has some reasoning behind it, and could thus be considered rational. Even take the case of, say, an ex-boyfriend stalking a woman because he still loves her - sure, we all know that it’s a really stupid way to try to win her back, but in the stalker’s eyes, he’s making rational decisions. It may be stupid, and it may harm more than help in the long run, but just about all decisions (and I say “just about” not because I can think of any exceptions, but to cover my own butt) are rational.
I’m going to tentatively go so far as to say that it is impossible for the average person to act irrationally at all. You want to prove me wrong? Go ahead. Do something irrational. But then your irrational act is being performed to prove me wrong, so there is reasoning behind it, and thus it is rational.
Now it’s possible that someone may have some sort of mental disorder in which they behave irrationally, but I think this is probably rare. I think that “rational vs irrational” boils down to “deliberate vs random”. If you’re making a deliberate decision to perform an action, that action is probably rational.
Or maybe I’m just rationalizing too much.
Jeff
I’m at home, my work box is on the fritz and I’ve had a few beers, so bear with me. Try searching for the Allais paradox for stuff of this nature. This page asks the questions (Click here to see if you are rational!).
It is possible to get evidence of apparent preference reversals via framing effects. IIRC the problem was first put by Amos Tversky who suspected Israeli generals’ answers to questions about how many lives they were prepared to spend to acheive a particular objective were inconsistent with what they said they were prepared to spend in order to save a life.
now recast exactly the same information in terms of survivors, to wit[not really a quote]:
Result?
There are sundry other examples, including one startling one about chocolate bars and coffee mugs which I’ll relate some other time.
And for what it’s worth I loved sunstone’s post. If we were fully rational, discussion would be unneccessary. If we were immune to the charms of reason, it would be pointless.
I am not sure I agree with this Allais Paradox conclusion based as a demonstration of rational choice.
[um, spoiler? If you haven’t followed that link or don’t know what the link mentions]
Let us say that there is a set of choices, {A,B}. Then we have {C,D} which is the same as {A,B} only the chances of success are drastically reduced (in this case, the probability of {C,D} is twenty five percent of {A,B}. We should like to say that a rational decision is one in which the choice is the same. Since {C,D} is the same choice in a different garb (we assert), if a person chooses A then they should choose C if they are rational.
Is this the case, though? This presumes that my reasons for taking D are the same as they were for taking A (or that they should be), which they most assuredly aren’t. I took A because it was a sure thing (as the main reason, though there were other factors). Since neither C nor D were a sure thing, and since the difference in probability wasn’t that great, it made more sense to try for more money.
I mean, you change the situation and I say the method of judgement changes as well. Is that more or less rational?
Let me say, I am not making a contrary assertion but rather scratching my head in 
You change the situation and wonder why you don’t get the same result?
However, the question you offer me directly is far more intriguing to me. Alas, I am still inclined to say that man is a rational animal, albeit not necessarily one that looks at choices in a neutral manner. “I judged this way because I saw it like this.” There was clearly a reason for that choice. Of course, the framing of the question changes the perspective it is looked at in the general case. But this is true for all investigations, is it not? I mean, how often is it that we say, “But look at the problem this way…” and then we suddenly see an obvious solution which previously escaped us.
Which is to say, we are basically as rational as the frame in which the choice is viewed. Most people probably do not seek to adjust the frame to be a perfectly rational frame, because the focus is on the choice.
I want to say: “Man is a rational animal because when we ask him why he has done such-and-such he can answer us.” Which is to say, he had a reason, he thought about it, and so on. His method of looking at the problem was not clearly based in reason.
Perhaps I should qualify my version of “rational man” to not demand consistency over time or method of introducing otherwise equivalent choices. Which is starting to sound like I am making “rational” mean nothing. 
Good stuff to think on.
How about: is there any way for one man to demonstrate to another man that man is not a rational animal? What form would this process take? And wouldn’t any demonstration assume that man can see the rationality behind it, and that the man demonstrating it was acting rationally in the first place?