Consonant mutation is a feature in languages when the sound of a consonant changes depending on morphology and syntax.

In English, the plural morpheme -(e)s and the singular third-person present tense morpheme -(e)s all have different pronunciations depending on which depending on which type of phoneme, or unique sound, comes before it. These variations of the plural morpheme are called allomorphs.

• If the base word ends with a voiceless stop like /p/, /t/, or /k/, then -(e)s will be pronounced /s/, like in lips, cats, and socks.
• If the base word ends with a sonorant, like /b/, /d/, /g/, /n/, /m/, /ŋ/, /l/, /ɹ/, or any vowel sound, then -(e)s will be pronounced /z/, like in cabs, lids, dogs, cans, rims, wings, bowls, cars, bows, toys, laws, and trees.
• If the based word ends with a sibilant or an affricate, like /s/, /z/, /ʃ/, /ʒ/, /t͡ʃ/, and /d͡ʒ/, then -(e)s will be pronounced /ɪz/, like in cases, mazes, washes, mirages, patches, and wages.

In English, the past tense morpheme -(e)d also has different pronunciations depending on which depending on which type of phoneme comes before it.

• If the base word ends with a voiceless consonant like /p/, /k/, /f/, /s/, /t͡ʃ/, then -(e)d will be pronounced /t/, like in licked, packed, laughed, passed, and pitched.
• If the base word ends with a voiced sound, like /b/, /g/, /n/, /m/, /ŋ/, /l/, /ɹ/, or any vowel sound, then -(e)d will be pronounced /d/, like in stabbed, lagged, sinned, hummed, hanged, bowled, scored, played, bowed, skied, and mowed.