In some philosophies of mind a commitment may be thought of as functioning slightly differently from a belief. One may be committed to a proposition in the sense of relying on it, or using it to structure explanation and prediction, but entirely in an instrumentalist spirit, and therefore without supposing it to be true. See constructive empiricism. Moral and aesthetic opinions may also be called commitments, and opposed to beliefs by being thought of as expressions of attitude. See expressivism, projectivism.