This paper focuses on two types of definites in Greek – MONADICS and POLYDEFINITES – and provides a constraint-based account of their form, meaning and use. Specifically, I discuss three core issues that have not been addressed in previous work. First, the special pragmatic import of polydefinites. These are associated with contextual constraints that go beyond the uniqueness entailments of standard (monadic) definites. Their idiosyncratic morphosyntax achieves effects similar to those induced in other languages solely by prosodic means and illustrated by phenomena subsumed within the term DEACCENTING. Second, the morphosyntax of definites. I argue that the Greek definite article can be best analysed as a PHRASALAFFIX, and provide a composition approach in the spirit of previous work couched in HPSG. Monadics and polydefinites are treated uniformly, without positing unmotivated complexity in the grammar for deriving the form of the latter. The definite concord and linear order facts that pose problems for previous analyses are directly derived and the morphosyntactic affinity between the Greek definite article and ‘weak form’ possessive is straightforwardly captured. Third, the semantics of definites. A quantificational semantics is provided that ensures that the semantic content of the definite article in polydefinites is integrated into the meaning of the sentence just once. Polydefinites are, therefore, semantically identical to monadics; the special import of the former originates from a contextual constraint on the anchoring of the index that interacts with the common morphosyntactic and semantic basis.