Abstract
<jats:p>Throughout the history of modern linguistics, numerous phonetic‐phonological diachronic developments have been identified as instances of assimilation or dissimilation. While scholars most often concur that a given sound change is the effect of one of these processes, there is still no consensus with respect to what causes them, whether they operate as two general principles in language or are simply labels for subgroups of widely diverging sound changes, and whether they are to be considered typically regular, sporadic, or both at the same time (depending on other factors). Although much recent work has been devoted to the representation of assimilation and dissimilation in formal grammars, the issues raised in this contribution remain rarely addressed and/or unresolved in diachronically oriented research.</jats:p>