Formation du Pluriel des Adjectifs

The plural of a French adjective is, in most cases, the same shape as the singular plus an -s. Petit → petits, grande → grandes, intelligent → intelligents. But three patterns deviate from that default — and the deviations are concentrated in masculine plurals, because the feminine plural is almost always regular. This page lays out the full system: the default rule, the no-change rule for adjectives already ending in -s or -x, the -al → -aux transformation with its small list of exceptions, and the -eau → -eaux pattern. We also cover the silent-s phonetics that make the plural mostly invisible to the ear and audible only in liaison contexts.

The default rule

Take the singular form (whatever its gender) and add -s.

This applies to the vast majority of adjectives: grand → grands / grandes, intelligent → intelligents / intelligentes, fatigué → fatigués / fatiguées, content → contents / contentes, bleu → bleus / bleues, froid → froids / froides, vert → verts / vertes, fort → forts / fortes, intéressant → intéressants / intéressantes.

The plural -s is silent in nearly all contexts. Petit and petits are pronounced identically — both /pəti/. The article (un / des, le / les) does the work of marking number for the ear; the adjective's -s is a writing-only signal. This is the single most important fact about French adjective plurals: the rule is mandatory in writing, but invisible to the ear.

Liaison with plural -s

The plural -s on an adjective produces a /z/ sound when the next word begins with a vowel or silent h:

This liaison happens with adjectives that precede the noun (BANGS) — that is, in exactly the position where the plural -s is most likely to be followed by a vowel. After the noun, the plural -s is rarely audible. Des chats noirs is /de ʃa nwaʁ/ — no liaison, because the adjective is at the end of the noun phrase and there is no vowel right after.

-s and -x endings: no change in masculine plural

If an adjective's masculine singular already ends in -s or -x, the masculine plural is identical. The ending is already a "plural-style" consonant.

Common members:

• -s: gris, français, anglais, japonais, bas, gros, épais, frais, mauvais, précis, exquis.
• -x: jaloux, heureux, sérieux, amoureux, vieux, doux, roux, faux, furieux, paresseux, peureux.

The feminine forms still take a regular -s in the plural: jalouse → jalouses, française → françaises, grosse → grosses. So you get un Français / des Français, une Française / des Françaises. The asymmetry between masculine (no change) and feminine (regular -s) is consistent across this entire class.

-al → -aux (most cases)

Adjectives ending in -al take -aux in the masculine plural. This is the most striking irregularity in the plural system, because the change is visible — the l disappears and is replaced by -ux.

Common members: national, international, régional, général, principal, spécial, amical, brutal, commercial, fondamental, égal, idéal (also idéals), immoral, libéral, littéral, loyal, machinal, médical, municipal, normal, occidental, oriental, original, partial, patronal, prénatal, radical, vertical.

The feminine of -al adjectives

The feminine of -al adjectives is regular: national → nationale, principal → principale, général → générale. The feminine plural is also regular: nationales, principales, générales. So only the masculine plural takes -aux; the feminine and the singulars are all built on the -al / -ale base.

This is a frequent slip: learners sometimes write des équipes nationaux, applying the -aux template to the feminine plural. The -aux form is masculine-plural only.

Exceptions: -al → -als

A small list of -al adjectives takes a regular -s in the masculine plural instead of -aux. Memorize the list — it is closed and short.

• banal → banals
• fatal → fatals
• final → finals (sometimes also finaux — both are accepted)
• naval → navals
• bancal → bancals
• natal → natals
• glacial → glacials (sometimes also glaciaux)
• tonal → tonals

Why these specific exceptions? Some are technical or recently borrowed terms (naval, bancal, tonal); others are conceptually unique enough that the plural is rare in practice (natal — most people have only one birthplace; fatal — once something is fatal, the matter is settled). The -als form preserves the unmarked-looking morphology for these special cases.

A few like idéal and final admit both forms with a slight nuance: des idéals in everyday speech, des idéaux in elevated or philosophical writing. When in doubt, look the word up — but the safe default for the -al class is still -aux.

-eau → -eaux

Adjectives ending in -eau take -eaux in the masculine plural — exactly like the noun pattern (château → châteaux, bateau → bateaux).

Members: beau → beaux, nouveau → nouveaux, jumeau → jumeaux. The closely related adjective hébreu (Hebrew) ends in -eu rather than -eau but follows the same pattern: hébreu → hébreux.

The feminines are regular and add -s normally: belle → belles, nouvelle → nouvelles, jumelle → jumelles.

The plural -x in beaux and nouveaux is silent — but it produces a /z/ sound in liaison: de beaux arbres /də bo.z‿aʁbʁ/. So even though it is spelled with x, it functions just like a plural -s.

Feminine plurals: regular across the board

Across all the patterns above, the feminine plural is built by adding -s to the feminine singular. Always.

• grande → grandes
• heureuse → heureuses
• italienne → italiennes
• blanche → blanches
• nationale → nationales
• belle → belles
• vieille → vieilles
• publique → publiques

This is the simplest part of the plural system: regardless of how irregular the masculine and feminine singulars look, the feminine plural just adds -s to the feminine singular. So once you have the feminine singular right, the feminine plural is free.

Quick-reference master table

Why the masculine plural is the trouble spot

Across all the patterns above, every wrinkle in plural formation lives in the masculine plural. The feminine plural is always feminine singular + s. The singular forms are the basis. So when you are checking whether you have the plural right, the only column that needs serious attention is the masculine plural — that is where -s/-x invariance, -al → -aux, and -eau → -eaux all show up.

This is a useful piece of mental architecture: when you encounter a new adjective, learn its four forms, but pay extra attention to the masculine plural, because that is where the surprises hide. Vieux is the same in masculine singular and plural; bel in front of a vowel is masculine singular, but the plural beaux applies regardless of what comes next; national becomes nationaux but the feminine plural is the entirely regular nationales.

Why English speakers underweight this

In English, plural nouns take -s but adjectives never mark plural. Tall trees, red houses, interesting books — the adjective stays the same. So when an English speaker learning French builds a noun phrase, the impulse is to leave the adjective alone. The result is sentences like des grand jardins or des français étudiants. Both are wrong: French requires the plural -s on the adjective just as on the noun, and the adjective also has to follow the position rules.

Because the plural -s is mostly silent, the only way to drill this is to write a lot. Speaking will not catch most of the errors — the ear is forgiving. Writing forces you to make the adjective agree, every time, with every noun. After a few weeks of this, the agreement becomes reflexive.

Common mistakes

The first error is a transfer of the default -s pattern to the -al class — extremely common at A2. The second is the inverse: applying -aux to the feminine plural, where it does not belong. The third is failing to mark plural at all on a BANGS adjective. The fourth is over-correcting: students learn that adjectives need -s in the plural and apply it to heureux, not realizing the -x already does the work. The fifth is forgetting the -al → -als exception list.

Key takeaways

• Default: + -s on whatever singular form you have.
• -s and -x endings: masculine plural unchanged. Feminine plurals still take -s.
• -al → -aux in masculine plural; feminine plural is regular -ales.
• Exception list (-al → -als): banal, fatal, final, naval, bancal, natal, glacial, tonal.
• -eau → -eaux in masculine plural; feminine plural is regular (belles, nouvelles).
• Feminine plural is always feminine singular + -s. Always.

The plural system is small enough that you can keep the whole thing in mind at once. The masculine plural is where almost all the irregularity sits; the feminine plural is regular by construction. Get the masculine right and the rest is automatic.