Tense and Aspect are fundamental categories in the architecture of grammar. Both situate eventualities in time, but they do so in different ways: tense anchors the time of the event deictically to the time of the utterance, yielding present, past, or future distinctions, either directly or through the mediation of a reference time (Comrie 1985, Bybee 1992). Aspect, on the other hand, refers to the internal temporal constituency of the event, encoding distinctions such as perfective, imperfective, and ingressive, among others (Vendler 1957, Verkuyl 1972, Comrie 1976, Dowty 1979, Smith 1991).
In addition to the inflectional encoding on the verb? of Tense and Aspect, well attested cross-linguistically, another common strategy consists in analytic constructions, which combine auxiliary verbs, particles, or other functional elements with lexical verbs. This variation occurs not only cross-linguistically, but also language-internally, where some Tense/Aspect distinctions may be expressed synthetically and others analytically or periphrastically.
References:
Comrie, Bernard. 1985. Tense. Cambridge: Cambridge University Press.
Comrie, Bernard. 1976. Aspect. Cambridge Textbooks in Linguistics. Cambridge: Cambridge University Press.
Dowty, David. 1979. Word Meaning and Montague Grammar. The Semantics of Verbs and Times in Generative Semantics and in Montague’s PTQ. Synthese Language Library, Vol. 7. Dordrecht: D. Reidel Publishing Company.
Smith, Carlota. 1991.The Parameter of Aspect. Springer Dordrecht.
Vendler, Zeno. 1957. Verbs and times. Philosophical Review. 66. 143-160.
Verkuyl, Henk J. 1972. On the Compositional Nature of the Aspects. FLSS, Vol. 15. Dordrecht: D. Reidel Publishing Company.