The notion of syncretism may be viewed diachronically or synchronically. Diachronically it refers to a merger that occurred as a process leading to the neutralization of a formerly overt distinction. Synchronically, it refers to formally identical expressions that are kept morphosyntactically distinct elsewhere in the system (Baerman et al. 2005). In this paper, various patterns of case syncretism in different Puyuma varieties are observed. In Nanwang Puyuma, genitive and oblique are syncretic, while in other dialectal varieties the distinction is partially preserved. In comparing the case paradigms, we come to observe and investigate the notion of syncretism synchronically and diachronically. The comparison made among different dialectal varieties also enables us to reconstruct the case paradigm of Proto-Puyuma. The result of the reconstruction provides evidence which shows that phonological conservation does not necessarily entail morphosyntactic conservation: Nanwang Puyuma is phonologically more conservative but is morphosyntactically more innovative. Second, by virtue of the comparison among the Puyuma dialectal varieties, we can detect how the diachronic changes may be invoked and infer how syncretism in morphology can be compensated via other morphosyntactic means.