Sohn, Chang Yong. 2005. Unifying Quantitative Changes in Middle English. English Language and Linguistics 19, 215-234. This paper proposes a unified account of ME quantitative changes within the framework of Optimality Theory. Unification of apparently diverse quantitative alternations is proven to be achievable through various interactions among a fixed set of constraints. It is demonstrated that both the syllable cut theory by Murray (2000) and the augmented foot by Lahiri and Dresher (1999) not only fail the test of observational adequacy but also are incompatible with crosslinguistically attested syllable types and foot types. It is argued that all changes can be functionally united by their endeavor to arrive at the optimal structure of a bimoraic head foot by satisfying two pivotal constraints, BtFin and NonFin. In addition the differences between ME quantitative changes with respect to the cause and effect are shown to be attributable to well- motivated prosodic constraints.