Prononciation des sons S et Z en français

What is the difference between “ils sont” and “ils ont”?

Ils sont and ils ont are different verbs that sound almost identical out loud. The only signal is the liaison: ils ont links with a buzzing [z] — “il-zon” — while ils sont keeps a hissing [s] — “il-son.” Lose that contrast and elles ont raison (“they’re right”) turns into elles sont raison, which means nothing at all.

The same pair runs right through the language: nous avons [z] against nous savons [s], ils aiment against ils s’aiment. French [s] is voiceless and [z] is voiced — rest a hand on your throat and only the [z] hums. The written shortcut is worth drilling too: a single s between two vowels is normally [z] (poison), a double ss is [s] (poisson).