Assimilation is a phenomenon occurring at word boundary where two words are combined.
It is the process that the single final consonant phoneme of the first word changes to become like the single initial consonant phoneme of the second word (neighbouring word) or the process that the single initial consonant phoneme of the neighbouring word changes to become like the final consonant phoneme of the first word.
Types of assimilation:
Progressive assimilation (đồng hóa xuôi): is the process that the preceding consonant assimilates the following one. Example: read these [ riːd ðiːz ] → [riːd diːz ]
Regressive assimilation (đồng hóa ngược) : is the process that the preceding consonant is assimilated by the following consonant. Example: that person [ðæt pɜːsn ] → [ðæp pɜːsn] , right place [ raɪt pleɪs ] → [raɪp pleɪs ]
In order to know which ways a consonant changes, we look through the main difference between consonants are of three types:
1. Differences in place of articulation
2. Differences in manner of articulation
3. Difference in voicing