diachronic phonology

Diachronic phonology is the study of how speech sounds and sound systems change over time within a language. It is a subfield of historical linguistics, which examines linguistic change in general. For instance, diachronic phonology would investigate why words that were once pronounced differently, like "sea" and "see" in English, now sound the same.12

This field contrasts with synchronic phonology, which analyzes sound patterns at a single point in time. Diachronic linguistics also studies sound changes like assimilation, where sounds become more similar to neighboring sounds, and dissimilation, where sounds become less similar. These changes can lead to significant shifts in a language's sound system over centuries.132