It is argued in this paper that the downsteps which mark the associative construction in Igbo and the set of "Class I" words in Kikuyu are best analyzed as morphemes of the form [ ꜜ ], where the symbol " ꜜ " represents a drop in pitch. If lexical tone contours are represented dynamically, as sequences of pitch rises ( ꜛ 's) and pitch drops ( ꜜ 's), then the interaction of the downstep with the surrounding tone contour can be accounted for in a coherent way by means of rules which move or delete pitch changes which would otherwise lie too close to another pitch change. In the final. section of the paper, this approach is extended to alienable possessive
phrases in Asante Twi, whose special tonal properties are shown to result from the presence of an associative morpheme of the form [ t ].