|Abstract:||Complementary distribution stems from two sources. The first is a consequence of static lexical regularities such that two sounds never appear in the same context. The second is from dynamic alternations induced by morphological derivation. In this paper I provide evidence -- from New York English, Akan, Madurese, and Malay -- that these two sorts of relationship among sounds possess distinct phonological properties. Sounds engaged in a static complementary relationship remain nonalternating upon reduplication/truncation, thus maintaining identity between a base and its relation. By contrast, dynamic phonotactic constraints induce identity-defeating alternations, provided the triggering context is present upon reduplication/truncation. These observations show that approaches that posit base-reduplicant/truncatum identity constraints miss the proper generalization regarding reduplicative and truncatory patterning.