The fact that only humans above a certain age can be morally virtuous, rather than babies or cats, means that that being moral requires some cognitive ability. If virtue is about desires, it is worth remembering that you can't desire some things without being able to conceive of them. Suppose a virtuous person will desire to make people happy and desire to tell the truth. You can't desire to make people happy without having the concept "happy" and you can't desire to be truthful if you don't have have the concept "lie", so a cat or a baby cannot desire these things.

I don't think we are all irrational every time we fail to see through an argument in a book, but suppose it's true about you. You are still more rational than you think you are. You are irrational in a minor way - believing a misguided theory of the nature of rationality - but rational in a major way - you respond well to probabilistic evidence as you go through the day.

Sometimes we deliberate - for example when we plan a long trip or - if we are not math wizards - when we solve long division problems. However, if we deliberated every time we acted we would never get through the day. Most of the time, we act for reasons without deliberation. I am not just talking about cases of simple, habitual action, like brushing your teeth, but also about more sophisticated action.

I am not committed in any way to the traditional concept of character - the concept of "character trait" as involving predictable behavior. I am committed to a view in the neighborhood - the view that the moral worth of one's actions depends on the quality of will expressed in them.

Suppose whether or not someone tells me a lie depends only on whether he wants to, but he is morally indifferent, he doesn't care much about the truth or about me, and his self interest, which he worships, tells him to lie, and so it comes about that given his psychology, it is a forgone conclusion that he will lie to me. I think in this case he is still blameworthy, and that implies, among other things, that he did something he ought not do.

If I make a stupid decision but don't execute it because I'm, say, lazy, then I'm lucky, not rational. However, at other times a person acts for good reasons just as she does what she thinks she shouldn't do, not knowing that they are good reasons. Just like sometimes we are a lot less rational than we think we are, it is also true that sometimes we are a lot more rational than we think we are.

Moral virtues and intellectual virtues are very different from each other, and moral virtue has to do with motivation, not cognition. Moral virtue requires a human level of intelligence, but it doesn't require that one be an intelligent human.