In Middle English, consonants and vowels altered values, and new phonemes appeared. Particularly, the distinction between the /f/ and /v/ consonants began to differentiate words (i.e. grief compared to grieve) and /s/ and /z/ (i.e. seal compared to zeal). The "ng" sound at the end of the word became contrastive (Old English "g" was always sounded). In the end, all vowels changed and the sound's spelling was altered (mainly due to French conventions).