This article argues that there can only be one chunk-defining device in grammar: a theory cannot afford to have the same work done twice, once by phases, a second time by prosodic constituency. As it stands, however, phase theory is unable to describe all phonologically relevant chunks; these are too small and too diverse to be delineated. To qualify as the only chunk-defining device in grammar, phase theory therefore needs to be made more flexible—that is, to be adapted to the demands of phonology. To allow phase theory to describe all phonologically relevant chunks, we propose the separation of the Spell-Out operation from the Phase Impenetrability Condition (PIC). When Spell-Out occurs, every access point may or may not be associated with a PIC at PF, and the same optional endowment with a PIC holds for syntax. This is what we call Modular PIC. Empirically, on the basis of Abruzzese raddoppiamento fonosintattico and data from Bantu, we show that PIC effects in syntax and phonology are entirely independent: a given Spell-Out operation may leave traces in both modules, in either one, or in neither.

In this article, we propose a phase-based alternative to Kayne’s (1989) analysis of past participle agreement in Italian. This analysis captures the principal facts without making reference to specifier-head agreement. Instead, the possibility of overt past participle agreement is determined by the Phase Impenetrability Condition and is linked to the surface position of the past participle. The analysis has interesting crosslinguistic implications, notably in that it predicts a general asymmetry between subject and object agreement.