Liaisons interdites
Some French liaisons are forbidden: they aren’t—can’t be—pronounced even in the most formal French. Sometimes this is to avoid confusion with similar expressions, sometimes it has to do with a sort of respect for names and foreign words, and other times there’s no apparent logic to it.
1. | Before h aspiré | IPA | |
en haut | [ã o] | [a(n) oh] | |
les héros | [le e ʁo] | [lay ay roh] | |
deux homards | [dø o maʁ] | [deu oh mahr] | |
2. | Before onze and oui | ||
les onze enfants | [le ɔ̃ zã fã] | [lay o(n) za(n) fa(n)]* | |
deux oui et un non | [dø wi e œ̃ nɔ̃] | [deu wee ay u(n) no(n)] | |
3. | After names | ||
Robert a 15 ans. | [ʁo bɛ ʁa kɛ̃ zã] | [ro beh ra keh(n) za(n)] | |
Nicolas est prêt. | [ni ko la ɛ pʁɛ] | [nee ko la ay preh] | |
4. | After singular nouns | ||
mon chat aime jouer | [mɔ̃ ʃa ɛm ʒwe] | [mo(n) shah ehm zhoo ay] | |
un garçon intelligent | [œ̃ gaʁ sɔ̃ ɛ̃ tɛ li ʒã] | [gar so(n) eh(n) teh lee zha(n)] | |
5. | After et | ||
avant et après | [a vã e a pʁɛ] | [ah va(n) ay ah preh] | |
un homme et une femme | [œ̃ nɔ me yn fam] | [u(n) nuh may un fahm] | |
6. | After interrogative adverbs** and toujours | ||
Comment est-elle ? | [kɔ mã e tɛl] | [ko(n) ma(n) eh tehl] | |
Combien en vois-tu ? | [kɔ̃ bjɛ̃ ã vwa ty] | [ko(n) byeh(n) a(n) vwah too] | |
Quand aimes-tu étudier ? | [kã ɛm ty e ty dje] | [ka(n) ehm too ay too dyay] | |
toujours aimable | [tu ʒu ʁɛ mabl] | [too zhu reh mahbl(eu)] | |
7. | After inversion | ||
A-t-on osé ? | [a tɔ̃ o ze] | [ah to(n) oh zay] | |
Parlez-vous espagnol ? | [paʁ le vu ɛ spa ɲɔl] | [par lay voo eh spah nyuhl] | |
Ont-elles étudié ? | [ɔ̃ tɛ le ty dje] | [o(n) teh lay too dyay] | |
Vont-ils habiter bien ? | [vɔ̃ ti la bi te bjɛ̃] | [vo(n) tee lah bee tay byeh(n)] |
* Note that the pronunciation of the z in onze at the beginning of enfants is enchaînement, not a liaison.
** Also see required liaisons and optional liaisons

if there’s no liaison after toujours, why is it pronounced tou-jou-REH-mabl?
Liaison is only with normally silent letters, like the “s” at the end of toujours. The “r” in toujours is always pronounced. When that happens – when a sound that is always pronounced is attached to the next word – that is called enchaînement.