I argue that the semantic content of thoughts and the linguistic meaning of expressions are things with a history in the sense that they can be made fully intelligible only from the point of view of the future. I defend this position by articulating a version of a view known in the philosophy of language as temporal externalism. Temporal externalism about content is the view that the content of a subject’s thoughts and utterances at a time t depends on features (...) of the linguistic practices of her community after t. There are two different ways in which temporal externalism can be developed. First, one can take it to be the view according to which the meaning of an expression is given by the whole pattern of use, including future ones, of that expression. Alternatively, one can interpret temporal externalism as the view that the meaning of a speaker’s utterance is determined by the norms that govern or constrain her linguistic behaviour. These norms, which may be instituted at a later date, place their authoritative stamp upon prior conduct. I show that the first version of temporal externalism faces severe objections from which the second version is immune. I also provide a defence of this second position through an extensive discussion of some thought experiments. (shrink)