Consonant voicing and devoicing

For example, the English suffix -s is pronounced when it follows a voiceless phoneme (cats), and when it follows a voiced phoneme (dogs). This type of assimilation is called progressive, where the second consonant assimilates to the first; regressive assimilation goes in the opposite direction, as can be seen in have to .

English

English no longer has a productive process of voicing stem-final fricatives when forming noun-verb pairs or plural nouns, but there are still examples of voicing from earlier in the history of English:

• belief () – believe ()
• shelf () – shelve ()
• grief () – grieve ()
• life () – live ()
• proof () – prove ()
• strife () – strive ()
• thief () – thieve ()
• bath () - bathe ()
• breath () - breathe ()
• mouth (, n.) – mouth (, vb.)
• sheath () - sheathe ()
• wreath () - wreathe ()
• advice () – advise ()
• house (, n.) – house (, vb.)
• use (, n.) – use (, vb.)

Synchronically, the assimilation at morpheme boundaries is still productive, such as in:

• cat + s → cats
• dog + s → dogs ()
• miss + ed → missed ()
• whizz + ed → whizzed ()

The voicing alternation found in plural formation is losing ground in the modern language,. Of the alternations listed below many speakers retain only the pattern, which is supported by the orthography. This voicing of is a relic of Old English, at a time when the unvoiced consonants between voiced vowels were 'colored' by an allophonic voicing (lenition) rule → . As the language became more analytic and less inflectional, final vowels or syllables stopped being pronounced. For example, modern knives is a one syllable word instead of a two syllable word, with the vowel e not pronounced and no longer part of the word's structure. The voicing alternation between and occurs now as realizations of separate phonemes and . The alternation pattern is well maintained for the items listed immediately below, but its loss as a productive allophonic rule permits its abandonment for new usages of even well-established terms: while leaf~leaves in reference to 'outgrowth of plant stem' remains vigorous, the Toronto ice hockey team is uncontroversially named the Maple Leafs.

• knife – knives
• leaf – leaves
• wife – wives
• wolf – wolves

The following mutations are optional:

• bath () - baths ()
• mouth () - mouths ()
• oath () - oaths ()
• path () - paths ()
• youth () - youths ()
• house () – houses ()

Sonorants () following aspirated fortis plosives (that is, in the onsets of stressed syllables unless preceded by ) are devoiced such as in please, crack, twin, and pewter.

Several varieties of English have a productive synchronic rule of /t/-voicing whereby intervocalic /t/ not followed by a stressed vowel is realized as voiced alveolar flap [ɾ], as in tutor, with the first /t/ pronounced as voiceless aspirated [tʰ] and the second as voiced [ɾ]. Voiced phoneme /d/ can also emerge as [ɾ], so that tutor and Tudor may be homophones, both with [ɾ] (the voiceless identity of word-internal /t/ in tutor is manifested in tutorial, where stress shift assures [tʰ]).