In this thesis, I attempt to lay out a comprehensive survey of *ABA patterns in case morphology—that is, patterns whereby a certain realizational rule can never apply to both case x and case z without also applying to case y. I show, more specifically, that such *ABA patterns can be found in systematic case syncretism, in case-conditioned wholesale suppletion, and in case-conditioned stem-formative allomorphy. I also argue that, crucially, the universal *ABA patterns evidenced by all these phenomena consistently make reference to the very same case classes, as encapsulated in (i). (i) a. If a systematic syncretism covers both an unmarked core case (nominative or absolutive) and an inherent case (dative, instrumental, locative, etc.), it wil...