This chapter evaluates alternative theories of vowel reduction and contrasts them with Mora Loss and Restoration (MLR) Theory. Some models reject non-moraic syllables, attributing vowel shortening to phonetic effects. Experimental evidence from New Zealand English and European Portuguese shows that durational and phonological differences among reduced vowels cannot be explained by phonetics alone, supporting a moraic distinction between short and super-short vocoids. Sonority-based theories (e.g. de Lacy 2006) treat reduction as avoidance of high-sonority vowels in unstressed positions, but overpredict unattested patterns and fail to capture durational contrasts. By contrast, Crosswhite’s (1999, 2001) contrast-enhancement theory explains reduction as maximizing perceptual distinctiveness, yet cannot account for asymmetrical vowel-raising patterns or cases where unstressed vowels uniformly lower to [a]. Feature-loss-only accounts (e.g. van Oostendorp 1995) recognize centralization but overlook moraic structure as the initial trigger. The chapter argues that MLR Theory best explains vowel reduction, deriving it from mora loss with optional feature loss and mora restoration.