Assimilation (phonology)

In phonology, assimilation is a sound change in which some phonemes (typically consonants or vowels) change to become more similar to other nearby sounds. This process is common across languages and can happen within a word or between words. For example, in English the plural suffix -s alternates voicing depending on the preceding consonant: pots /pɒts/ versus pods /pɒdz/.

It occurs in normal speech but is more frequent in faster speech. Sometimes the change is accepted as canonical, and can even become recognized in standard spelling: implosion pronounced with [m], composed of in- + -plosion (as in explosion).

Sound segments typically assimilate to a following sound, but they may also assimilate to a preceding one. Assimilation most commonly occurs between immediately adjacent sounds but may occur between sounds separated by others. For example, in handbag /ˈhændbæɡ/ the [d] is sometimes elided (omitted) in rapid speech, which causes the [n] to assimilate to [m], becoming [ˈhæmbæɡ], as [m] and [b] are both bilabial (produced with both lips) in their place of articulation.

Assimilation can be synchronic, an active process in a language at a given point in time, or diachronic, a historical sound change—for instance, cupboard, historically a compound of cup (/kʌp/) and board (/bɔːrd/), is now pronounced /ˈkʌbərd/, with the original /ˈkʌpbɔːrd/ almost never used.

A related process, coarticulation, includes changes like vowels nasalizing (taking on a nasal sound) before nasal consonants (/n, m, ŋ/) due to premature soft palate (velum) lowering, or /b/ labializing (lips rounding) as in boot ([bʷuːt̚]) or ball [bʷɔːɫ] in some accents. This article describes both processes under the term assimilation.