Suppose a student of mine writes in her exam that "morality is completely relative to culture, so nothing is absolutely right or wrong. Because of that, it is absolutely wrong to be culturally intolerant". This student, if she believes what she writes, believes a contradiction. She ought not to believe the contradiction - it's a basic epistemic norm. This is true even if she can't avoid believing it - no amount of studying will show her the light.

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.

A person is praiseworthy for a right action to the extent that her action manifests, and is rationalized by, good will, that is, concern for the right and the good, not necessarily under the description "right" or "good". A person is blameworthy for a wrong action to the extent that her action manifests, and is rationalized by, ill will - concern for the wrong and bad, also de re - or moral indifference - lack or deficiency of good will.

When you find yourself reluctant to sit on a chair because it had unexpectedly collapsed in the past you might shake your head and think "there, I'm so irrational!". But your reluctance to sit on a probably rickety chair is not irrational - you think it's irrational because you have a false view of what irrationality is.

I think it's ok to have wishes that conflict with each other - it's irrational to try to make them both come true, but not irrational simply to have them.

Duties concern things that are voluntary. I do think that if you have a moral duty to bring me back the book you borrowed, that implies, roughly, that your doing so depends on your wanting to do so: if you want to bring me the book, you will. This is not the case if you are stuck at some airport due to a snowstorm, far away from me. This, however, is not the same as "ought" implying a metaphysical "can".

A very tall man once asked a question after my talk. Before beginning his question, he explained that the reason he was standing up is not to be intimidating but rather to make eye contact. His question was essentially "are we really interested in moral motives? Isn't it all about action?". I pointed out to him that it was not enough for him to do the right thing - stand up - but he also wanted me to know that he is doing it from the right motive or for the right reason - to make eye contact, rather than to be intimidating. Voila, moral psychology.