In this paper we focus on the syntactic behavior and interpretive properties of the complex temporal constructions headed by antes/después (Spanish) and prima/dopo (Italian) ‘before/after’ with the aim to offer an analysis for their syntactic internal structure. These constructions refer to a precise point in time that has to be deduced by the hearer through an inferential process, which involves a computational operation. Adopting the cartographic hypothesis (cf. Cinque, 1994, 1999), according to which in natural languages grammatical categories –features and/or heads– are active in syntax even when they are not phonologically expressed, we propose that antes/prima ‘before’ and después/dopo ‘after’ are the morphological reflections of a series of features: the subtractive or additive feature respectively, given that both elements behave like lexical comparatives, and vectorial features (cf. the proposal suggested by Svenonius (2006, 2007) for prepositional phrases expressing spatial relations).