Because partitive constructions (“a grain of rice,” “a cup of coffee”) are one of the ways of individuating referents in many languages, there is a need to establish the mechanisms to obtain appropriate representations for such compounds by composing partitive nouns and noun phrases that denote a whole of reference. Furthermore, some partitives are nouns that show a polymorphic behavior. Namely, depending on the context, they may be interpreted either as object referents or as partitives (e.g., “cup,” container vs. cointainee interpretations). This work discusses these and other related issues and posits representations intended to account for such phenomena in Spanish. The main claim is that the semantics of partitives largely depends on constitutive information. More specifically, the semantics of portions seems to be grounded on a generalized construal of any entity as being made of some stuff.