We explore the role of irregularity in sound change in signed and spoken languages. While all historical phonologists accept some kinds of irregularity in spoken language sound change, a full, rigorous accounting of where and why we find it has been harder to come by. We draw on the foundations of signed language sound change laid by Law, Power, and Quinto-Pozos to address this with a focus on irregularity. We begin to develop concrete parallels to irregularity in spoken language sound change, such as proposals for lexical diffusion. Throughout, we pay heed to where differences in modality do and do not make a difference.

It is well-known that English variable word-final coronal stop deletion (CSD) is less likely to occur when the final coronal stop instantiates the inflectional suffix -ed. It is sometimes hypothesised that the reason for this effect is to avoid the homophony between past and present tenses that would result from the suffix -ed being deleted. This reasoning suggests another hypothesis: that CSD should also be disfavoured when it would create homophony between two distinct lexical items, such as bald and ball. In this squib, we test that hypothesis on data from a corpus of Philadelphia English. We find no evidence that probability of CSD is affected by homophony avoidance between lexical items. This weakens the case that homophony avoidance is at play in disfavouring CSD in the -ed case, and may have implications for the theory of homophony avoidance in phonology in general.

Homophony avoidance has often been claimed to be a mechanism of language change. We investigate this mechanism in Dutch by applying two strands of research – corpus studies and experimental data – to find support for claims based on earlier historical observations. Throughout the history of Dutch, homophony avoidance has been named as the cause of language change or inhibition of change on several occasions. We build on these historical observations with an experimental study and a corpus study on a synchronic Dutch alternation, where avoidance of homophony between present and past tense can appear. Plurals of verbs with a stem ending in a dental show homophony with the present when they are used in the preterite (compare zetten ‘put’ pst-pl with zetten ‘put’ prs-pl). This homophony can be avoided by using the perfectum (hebben gezet ‘have put’). A wug-style experiment shows that verbs with dental stem are indeed used significantly more in the perfectum in the plural than in the singular, while verbs without dental stem do not show this difference. A corpus study on Dutch further corroborates these results. Combined, these studies make a strong case for homophony avoidance as a plausible mechanism of language change.