Morphology - Unit Four - Lesson No. 21

Assimilation and dissimilation

Assimilation is a phonological process that changes feature value of segments to make them more similar, e.g. a vowel becomes [+nasal] when followed by [+nasal] consonant (Fromkin 2009: 571).

Assimilation, an ease of articulation, is a process in which the sound influences the pronunciation of an adjacent or nearby sound (Fromkin 2009: 529). Generally speaking, assimilation occurs when sounds come to be more like each other in terms of some aspects of their pronunciation (Lieber 2009: 159).

Types of assimilation

There are three two types of assimilation: nasal and voiced. Nasal assimilation is subdivided into nasal consonant assimilation and nasal voiced assimilation.

1. Nasal assimilation

Nasal assimilation is of two types: consonant nasal assimilation and nasal vowel assimilation.

1.1. Nasal Consonant Assimilation

A nasal consonant assimilates to the point of articulation of a following consonant, and to the point and manner of articulation of a consonant if it is a liquid. The possessive prefix in Zoque is a nasal consonant that has three allomorphs (examples from Nida 1946/1976: 21 (cited in Lieber 2009: 160)):

pama “cloth” ʔəs mpama “my cloth”
kayu “horse” ʔəs ükayu “my horse”
tuwi “dog” ʔəs ntuwi “my dog”

1.2 Nasal Vowel Assimilation (Vowel Nasalization)

A vowel is nasalized when followed by a nasal consonant. That is, according to Fromkin (2009: 529), “because it is easier to lower the velum to produce nasality in advance of the actual consonant articulation. Once the vowel is nasalized, the contrast that the nasal consonant provided can be equally well-provided by the nasalized vowel alone, and the redundant consonant may no longer be pronounced”. For example, the vowels in these words are nasalized because they are followed by nasal consonants:
beam [bī:m]
bean [bī:n]

2. Voice Assimilation

The second type of assimilation is voice assimilation. Here, sounds become voiced or voiceless depending on the voicing of the neighboring sounds. The English regular past tense illustrates such kind of voice assimilation. The verbs that take the past allomorph [t] all end in voiceless consonants: [p, f, θ, s, ʃ, tʃ, k]. those that take the [d] allomorph all end either in a voiced consonant: [b, v, ð, z, ʤ, g, m, n, ŋ] or in a vowel (Lieber 2009: 160).


Dissimilation rules are phonological rules that change feature values of some segments to make them less similar, e.g. a fricative dissimilation rule: / θ/ is pronounced [t] following another fricative. In English dialects with this rule, sixth /siks + θ/ is pronounced [sikst] (Fromkin 2007: 544).

Unlike assimilation, dissimilation is a phonological process which makes sounds less like each other. In the regular past tense morpheme in English, a schwa separates the [t] or [d] of the past tense from the matching consonant at the end of the verb. For example,

  1. defeat → defeated
  2. bond → bonded

Again, this makes perfect sense phonetically. If the [t] or [d] were used, it would be indistinguishable from the final consonant of the verb root (Lieber 2009: 161).

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