Obligatory Liaison

French is famously a language where final consonants go silent. Petit is /pə.ti/, not /pə.tit/; les is /le/, not /les/; vous is /vu/, not /vus/. But there is a major exception: when the next word begins with a vowel, that silent final consonant comes back to life and links to the following word as a single syllable. This phenomenon is called liaison, and in some cases it is not just allowed — it is required. Skipping a required liaison sounds as wrong to a French ear as a missing plural -s sounds to an English one.

This page covers obligatory liaisons — the contexts where a French speaker will always make the link, and where omitting it marks you immediately as a learner. We cover optional liaisons (those that vary by register) and forbidden liaisons (those you must not make) on the other pages in this series.

What liaison is

When a French word ends in a consonant letter (typically -s, -x, -z, -t, -d, -n, -r) that is normally silent, and the next word begins with a vowel sound, that consonant is "released" and pronounced at the start of the next syllable.

The final -s of les is silent before a consonant (les chats /le.ʃa/), but before the vowel of amis it surfaces, and crucially it is pronounced /z/, not /s/. The liaison /z/ then forms the onset of the next syllable: le-za-mi, not les-amis.

Which sound the liaison consonant makes

The pronunciation of a liaison consonant is not always its written form. There is a small set of regular conversions:

The /z/ for written -s is the rule that surprises English speakers the most. The plural -s of les, des, mes, tes, ses, ces, nos, vos, leurs, deux, trois, six, dix is silent before a consonant but voiced as /z/ before a vowel. Once you internalize this, dozens of liaisons fall into place at once.

The -d turning into /t/ is the second-most-surprising rule. Grand ami is /ɡʁɑ̃.ta.mi/, not /ɡʁɑ̃.da.mi/. The -d devoices to /t/ in liaison.

When liaison is obligatory

Liaison is required in tightly-knit grammatical units — places where the two words form a single syntactic group. Below are the main obligatory contexts.

Determiner + noun

Articles, possessives, demonstratives, and numbers always liaise with the noun they introduce.

Notice in the last example that liaison fires twice: aux → États (/o.ze/) and États → Unis (/e.ta.zy.ni/). Liaison is not a one-shot rule; it triggers wherever its conditions are met within the same syntactic group.

Subject pronoun + verb (and inverted verb + pronoun)

Personal subject pronouns are inseparable from their verb. The link is always made, in both directions.

The inverted form (vient-il, parlent-elles) is built around an obligatory liaison. The hyphen in writing reflects the phonological link.

Pronoun + verb + pronoun (object pronouns)

Clitic object pronouns also liaise with the verb.

Adjective + noun (when the adjective comes before)

When an adjective precedes the noun (a smaller set of frequent adjectives — petit, grand, bon, gros, mauvais, ancien, premier, dernier, jeune), liaison is obligatory.

When the adjective comes after the noun (most adjectives in French), liaison is forbidden — see Forbidden Liaison.

Number + noun

Cardinal numbers liaise with the noun they count.

A surprising detail: the numbers cinq, six, huit, dix have a final consonant pronounced when they stand alone (cinq /sɛ̃k/, six /sis/, huit /ɥit/, dix /dis/), but silent before a consonant (cinq tables /sɛ̃.tabl/, six chats /si.ʃa/, dix maisons /di.mɛ.zɔ̃/), and resurfaced as /z/ before a vowel (six amis /si.za.mi/, dix ans /di.zɑ̃/). For six and dix specifically, the liaison form /z/ replaces the citation /s/. This three-way alternation is a hallmark of French phonology.

Preposition + complement

Short, very frequent prepositions (en, dans, sans, sous, chez) trigger liaison with whatever follows.

Auxiliary + past participle (in être / avoir compound tenses)

The auxiliary verbs être and avoir liaise with the past participle that follows.

Fixed expressions

A handful of frozen phrases carry obligatory liaison as part of their stored form, even if the syntactic context would not normally require it.

Comparison with English

English does not have anything quite like systematic liaison. The closest parallel is linking r in non-rhotic British English: the idea-r is good, where an r appears between a final non-high vowel and a following vowel. But English linking is much more limited and never involves resurrecting a written consonant that the speaker would otherwise treat as fully silent. In French, liaison is a load-bearing feature of every grammatical phrase, and you cannot speak fluent French without it.

The other comparison is with English plural -s: in cats, the -s is /s/; in dogs, it is /z/; in buses, it is /əz/. English speakers already perform consonant alternations they aren't conscious of. French liaison /z/ is similar — it is automatic for native speakers and needs to become automatic for you.

Common Mistakes

Key takeaways

Liaison is the resurrection of a normally silent word-final consonant before a following vowel. In the obligatory contexts — determiner + noun, subject pronoun + verb, prenominal adjective + noun, number + noun, frequent prepositions, auxiliary + past participle — making the link is not optional and not a matter of style. The consonant has predictable conversions: written -s/-x/-z surface as /z/, -t/-d as /t/, -n as /n/. Get these reflexes into your speech early; they shape the rhythm and connectedness that make French sound like French.