Semiticists recognize that pre-modern Northwest Semitic languages had vowel quantity distinctions, but disagree regarding whether quantity was lexical or was predictable from factors like stress or syllable structure. These discussions fail to recognize that quantity cannot be a function of syllable structure and stress if those parameters are themselves quantity-sensitive. In this paper the author proposes a metrical account of main stress in Jewish Literary Aramaic (JLA) under which stress and vowel reduction are governed by an end-right quantity-sensitive (moraic) trochaic foot. It follows that vowel quantity must be lexically specified in JLA for at least some vowels positions, and also that some JLA final vowels generally regarded as long were in fact short. This last conclusion heralds later developments in other Aramaic dialects. Finally, the author argues for some cases of final CV metathesis in JLA.