 A second problem for the diagonalization strategy is a problem of scope (Chalmers, 2002). Although the diagonalization strategy yields a truth-conditional notion of content, the only centered worlds at which the diagonal proposition is evaluated will be worlds that contain at their center the mental state we are interested in. In effect this means that every mental state represents itself as existing. But it is puzzling why I could not have mental states whose content has nothing to do with their own existence. Chalmers offers these examples (Chalmers 2002, p. 625): it seems that my thought that I am a philosopher should be true in worlds centered on a philosopher even if he is not currently thinking that he is a philosopher. Again, it seems that the thought that someone is thinking should be false, not undefined, at centered worlds that do not contain a thinking person.