Stem alternations and stem distributions

The analysis of stem alternations (e.g. sang as past of sing) is controversial; there is a lasting tension between morphophonological theories (sang is derived from sing by rule) and stem storage theories (sang and sing are stored allomorphs). This paper argues that in many cases of stem alternation (e.g., Spanish diphthongization) the locality conditions on contextual allomorphy provide crucial evidence for deciding between these views, and crucial evidence for a morphophonological theory in particular. However, the argument is only that some alternations must be treated morphophonologically; it is based only on one subtype of alternation. Another (“morpheme-morpheme”) type of alternation, one that applies only to certain morphemes, and which is triggered only by a particular morpheme (or morphemes), appears to take place under the same locality conditions that are obeyed by contextual allomorphy. In morpheme-morpheme alternations, distributional arguments based on locality conditions might not be able to decide between storage and morphophonology. At the same time, it can be shown that the two theories make different predictions about how such alternations are represented in the minds of speakers. This leads to a potentially unified theory, in which the boundaries between theoretical and experimental approaches are effectively eliminated.