When phonemes are joined together within single words and at the junction of words in phrases and sentences, they have a tendency to react one upon the other in such a way that the articulation of one phoneme influences the articulation of a neighboring phoneme making it similar to itself. This process is called assimilation.
In assimilation the phoneme whose articulation is modified under the influence of a neighboring phoneme is called the assimilated phoneme; the phoneme which influences the articulation of a neighboring phoneme is called the assimilating phoneme.
The term assimilation may also be extended to include cases when two adjacent phonemes so influence each other as to give place to a single new phoneme different from either of them.
Although assimilation is common to all languages, it does not act in the same way in all languages. In modern English it is mostly consonant phonemes that are affected by assimilation.
1. Verbs ending in /ed/
· the sound in the flection is assimilated under the influence of a vowel or voiced consonant, thus becomes [d]
· the sound in the flection is assimilated under the influence of an unvoiced consonant, thus becomes [t]
· after [t], [d] it sounds as [id]