I was just reading the bit of Gibbard's Thinking How to Live where he talks extensively about the good and the desirable—specifically, about its being a conceptual truth that they are one in the same. I know that this is a common line people take, and I'm curious how many of you agree with it, because I'm not entirely convinced.
Suppose classical utilitarianism were true. It might be that it would be good if my mother were dead, because this would save some large number of people from dying themselves. I'm really not sure it would be fitting for me to desire that my mother were dead.
Now, I'm not saying that it's entirely clear to me that it would not be fitting for me to desire this. I'm really not sure. But that lack of certainty—the apparent openness of the question—is enough to make me doubt that the identity is conceptual; so I'm curious why others take it to be.
One further thing: I wonder whether there is a connection between accepting this identity and the Humean theory of motivation. The relevant thought goes something like this: If X is good, then we ought to promote X. If we ought to promote X, then it is fitting for us to be motivated to promote X. If it is fitting for us to be motivated to promote X, then surely it is fitting for us to desire to promote X. If it is fitting for us to desire to promote X, then surely it is fitting for us to desire X itself. (I would be tempted to resist the last two moves, not to mention the Humean line itself.)