What does it mean to be "rational"? Sometimes when we say that a person "is rational" because their beliefs are well-justified in terms of evidence, reason, and logic. Other times, though, we mean that a person's actions are appropriate given their goals. Not only are these two senses of "is rational" very different, but they can even conflict with one another. Why is that?

Jonathan Ichikawa explains:

For instance, it's possible that a person just wouldn't want to know that his wife was cheating on him, and therefore might rationally (in the second sense) ignore evidence (which violates the first sense). Or, we can make up more fantastic scenarios -- if I could get myself to do it, it would be rational(2) for me to form the irrational(1) belief that the earth was flat if I could win a million dollars by doing so. Or it would be rational(2) for me to believe and use a the bad inference rule, A therefore (A & B), if I learned that God was planning to torture everyone who did not use that inference rule. (Come to think of it, this last case, which I intended to be fantastical, is pretty close to the situation given in 1984.)

So, given that we have two different meanings of "rational" which can conflict with one another, are they at all connected? Did one grow out of the other or vice-versa? If not, how did the same word come to be applied to such different ways of thinking? Is one mode of rationality "superior" to the other, such that second should perhaps be given a different label?

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