This dissertation presents a crosslinguistic study of the temporal semantics of noun phrases. Through an investigation of languages with ``nominal temporality markers'', i.e. markers that attach to noun phrases and affect their temporal interpretation, I propose that the semantic categories grammatical aspect and modality, but not tense, are relevant to the temporal interpretation of noun phrases. I propose a dynamic semantic theory of the temporal interpretation of noun phrases, which sheds light on similarities and differences to the temporal interpretation of verb phrases.

Previous discussions of the temporal interpretation of noun phrases (cf. Enç 1981, Musan 1995, Tonhauser 2002) are limited in two ways: they are restricted to data from English and German, and they do not discuss the semantic categories that play a role in the temporal interpretation of noun phrases (besides pointing out that verbal tense does not affect noun phrases). These limitations are remedied in this dissertation by drawing on data from languages with nominal temporality markers. About 20 such languages have been identified, including Guaraní (Tupí-Guaraní), Halkomelem (Salish) and Movima (isolate in Bolivia). I develop criteria for determining the semantic category of temporal expressions and propose that, crosslinguistically, nominal temporality markers instantiate the semantic categories grammatical aspect, modality and a novel category ``existence'' that is restricted to noun phrases. I defend this proposal against previous claims according to which the nominal temporality markers are nominal past and future tenses (e.g. Burton 1997, Lecarme 1999, Nordlinger and Sadler 2004).

The focus of the dissertation is Guaraní, a language with two nominal temporality markers. Based on data collected during fieldwork in Paraguay, I explore the morphosyntax, lexical restrictions, meaning and use of these markers, which, to the best of my knowledge, is the first detailed study of such markers. I develop a semantic analysis of the markers as grammatical aspect and modality markers, and show that they do not behave like tenses. The discussion of the Guaraní nominal temporality markers is couched in a larger study of the grammar of noun phrases and verbal temporality of Guaraní. One result of this study is that Guaraní is a (verbally) tenseless language. I compare the temporal interpretation of noun phrases in English and Guaraní and suggest that it is determined by the same constraint in the two languages. I identify two areas of crosslinguistic variation in the temporal semantics of noun phrases: the morphosyntactic realization of the semantic categories grammatical aspect, modality, and existence and the use of nominal temporality markers in particular discourse contexts.

I develop a dynamic semantic theory of the temporal interpretation of noun phrases where the time relative to which a noun phrase is interpreted is resolved according to the link between the denotation of the noun phrase and the discourse context. Contrary to previous proposals, I argue that the temporal interpretation of noun phrases does not depend on tense and, hence, is not parallel to that of verb phrases. I support this claim by pointing to several empirical differences in the way in which noun phrases and verb phrases are temporally interpreted. Further motivation for a tenseless analysis of the temporal interpretation of noun phrases is the finding that none of the languages with nominal temporality markers provide empirical evidence for nominal tense. Consequently, the temporal interpretation of both noun phrases and verb phrases depends on the discourse context, but on different facets of it: contextually given times are relevant for verb phrases, whereas the individuals of the discourse context are relevant for noun phrases.