This study examines phonetic correlates to three prosodic categories in Blackfoot: the syllable (σ), the prosodic word (ω), and the phonological phrase (φ). I provide evidence that the Blackfoot σ is recognizable by an obligatory process of vowel coalescence and the φ is recognizable by an obligatory process of right edge aspiration. The ω can be distinguished from these other two prosodic constituents by an optional phonetic process which mimics intersyllabic vowel coalescence, but does not apply obligatorily.The prosodic categories investigated in this study are then correlated to three morphosyntactic categories: morphological agreement suffixes, lexical morphemes (adjectives and nouns), and demonstratives. This correlation is used to argue that morphological and syntactic processes function differently at the interface with phonology (cf. Russell 1999), ultimately raising questions with "word-internal syntax" analyses of Blackfoot suffixation which are derived through cyclic head movement (Bliss 2013; Wiltschko 2014) using the Mirror Principle (Baker 1985).