Deriving the variation and constraints of the present perfect

I argue that the inferences and constraints of the English present perfect can be derived as a result of the competition with an alternative with stronger presuppositions, the simple past. I show that the English simple past, unlike the present perfect, presupposes uniqueness and anaphoricity of the topic time. By Maximize Presupposition, the present perfect is restricted to contexts in which the presuppositions of the simple past are not met. I also show that the crosslinguistic variation of the present perfect results from the availability of alternatives, by presenting data in several Romance and Germanic languages.