  Propositions are also commonly treated as the meanings or, to use the more standard terminology, the semantic contents of sentences, and so are commonly taken to be central to semantics and the philosophy of language. However, there is room for doubt about whether propositions are the right sort of entity for the job (Lewis 1980). Here is why. Note that a sentence would appear to contribute the same content regardless of whether it occurs as a proper part of a larger sentence. So, a sentence such as ‘in the past, Reagan was president’ would seem to be true depending on whether the content of ‘Reagan is president’ is true at some past time. But this would seem to imply that this content must lack temporal qualification — that it can change in its truth-value over time. Similarly, it seems there are locative sentential operators ‘in Chicago, it is raining’. If so, then by a similar argument, it would seem that the content of ‘it is raining’ would have to lack spatial qualification. The problem is this: it seems propositions, being the objects of belief, cannot in general be spatially and temporally unqualified. Suppose that Smith, in London, looks out his window and forms the belief that it is raining. Suppose that Ramirez, in Madrid, relying on yesterday’s weather report, awakens and forms the belief that it is raining, before looking out the window to see sunshine. What Smith believes is true, while what Ramirez believes is false. So they must not believe the same proposition. But if propositions were generally spatially unqualified, they would believe the same proposition. An analogous argument can be given to show that what is believed must not in general be temporally unqualified.