This paper presents evidence for abstract phonology—that is, a phonology that recognizes underlying segments which are not realized phonetically. Two underlying vowel segments /ᴐ/ and /ε/ are posited for Nupe (a Kwa language of Central Nigeria), both of which are realized as [a], therefore merging (‘absolutely neutralizing’) with /a/. Arguments based on pattern congruity, naturalness, and a ‘weak’ form of alternation are brought forth in support of this solution. Central, however, is the demonstration of the psychological reality of these two segments. In addition, various alternate solutions are shown to be inadequate. Finally, implications of the abstract Nupe solution are discussed.