Philosophical confusion often arises when we mistake grammatical impossibility for physical impossibility. Take the grammatically similar sentences "A has a gold tooth" and "A has a toothache." We may not see the gold tooth because it is physically imposs ible to see it (when the mouth in question is shut), whereas it is grammatically impossible to feel A's toothache.

Because in both cases we can say, "It is impossible to..." we may think that the impossibility is the same in both cases. However, in the case of a toothache, the impossibility is not simply a matter of circumstances that happen to prevent us from seeing. It is the grammatical impossible to talk logically about feeling other people's toothaches. The point is that there is not an experience called "feeling A's toothache" that is possible.