Consonant voicing and devoicing

In phonology, voicing (or sonorization) is a sound change where a voiceless consonant becomes voiced due to the influence of its phonological environment; shift in the opposite direction is referred to as devoicing or desonorization. Most commonly, the change is a result of sound assimilation with an adjacent sound of opposite voicing, but it can also occur word-finally or in contact with a specific vowel. For example, the English suffix -s is pronounced [s] when it follows a voiceless phoneme (cats), and [z] 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 [hæftə]. 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 ([f]) – believe ([v]) shelf ([f]) – shelve ([v]) grief ([f]) – grieve ([v]) life ([f]) – live ([v]) proof ([f]) – prove ([v]) strife ([f]) – strive ([v]) thief ([f]) – thieve ([v]) bath ([θ]) - bathe ([ð]) breath ([θ]) - breathe ([ð]) mouth ([θ], ()) – mouth ([ð], ()) sheath ([θ]) - sheathe ([ð]) wreath ([θ]) - wreathe ([ð]) advice ([s]) – advise ([z]) house ([s], ()) – house ([z], ()) use ([s], ()) – use ([z], ()) Synchronically, the assimilation at morpheme boundaries is still productive, such as in: cat + s → cats dog + s → dogs ([ɡz]) miss + ed → missed ([st]) whizz + ed → whizzed ([zd]) The voicing alternation found in plural formation is losing ground in the modern language,. Of the alternations listed below many speakers retain only the [f-v] pattern, which is supported by the orthography. This voicing of /f/ is a relic of Old English, at a time when the unvoiced consonants between voiced vowels were 'colored' by an allophonic voicing (lenition) rule /f/ → [v]. As the language became more analytic and less inflectional, final vowels or syllables stopped being pronounced.