This paper explores the formal correspondences between the members of verb pairs participating in the noncausal/causal alternation in Kagulu, a Bantu language from Tanzania. Our investigation shows that Kagulu has a predominance of equipollent verb pairs, with the anticausative and causative correspondences following close behind. We argue that, diachronically, the causative correspondence was much more prominent than it is in present-day Kagulu. However, due to morphophonological changes triggered by the historical causative suffix *-i, a significant number of verb pairs that are diachronically causative can be synchronically reanalyzed as equipollent. This study highlights the complexity of diachronic morphology in synchronic analyses of comparative-typological phenomena such as the noncausal/causal alternation, and contributes to the growing body of research on noncausal/causal verb pairs in African languages.