 The first global account of nonconceptual content, which was already mentioned above, is possible world semantics (see, e.g., Stalnaker 1984, 1998, Lewis 1979, 1986). According to proponents of this view, the content of a mental representation consists of a proposition, where propositions are taken to be functions from possible worlds to truth values, or alternatively the set of possible worlds in which the proposition is true. Beliefs and other propositional attitudes are then attitudes a person might hold towards such sets of possible worlds. For example, if one believes that Norman shot Susan, one has the belief attitude towards those possible worlds in which Norman actually did shoot Susan. This is merely to say that one takes the actual world to be a member of the set of possible worlds in which the proposition is true. Similarly, having a perception is having a representational state the content of which is the set of possible worlds in which the perception is correct.