The letters s and z are called alveolar fricatives.
In order to pronounce them, the flow of air must be stopped or impeded by creating a block or a small opening between the tongue and the alveolar ridge.
The difference between these two letters consists on the sonority, in fact s is voiced while z is voiceless.
- between two vowels:
- music, reason, cousin;
- when there is a vowel before s and after it -e:
- disease, choose, rose;
- plural third person conjugation:
- she loves, he chooses, it loses;
- exceptions with ss:
- dessert, scissors, possess, dissolve;
- after voiced consonants:
- dogs, beds, dolls.
The letter s is pronounced as ʒ when:
- it is between two vowels;
- there is a vowel before s and after it -e (exceptions: house, mouse, promise);
- we use s as a suffix or to add a suffix to form plural third person conjugation, however this does not always apply and you should remember the words by heart;
- there are some exceptions of words with double s (ss);
- used after the voiced consonants b, d, g, l, r, w, m, n, v, y.