The default rule for French adjective agreement is simple: match the noun in gender and number. But once you start writing real sentences, edge cases pile up. What gender does an adjective take when it modifies one masculine and one feminine noun? Does avoir l'air trigger agreement with the subject or with l'air? Is demi invariable, and if so, when? Why do compound color adjectives like bleu marine never agree, while a simple bleu always does? This page collects the special cases that go beyond the basic rules and explains what the traditional grammar says, what modern usage tolerates, and why the discrepancies exist. By the end, you should be able to handle the agreement decisions that catch out even native writers.
Compound subjects: masculine wins
When an adjective modifies two or more nouns of different genders, the masculine plural form prevails. This rule has nothing to do with sexism per se — it reflects an older conception of grammatical gender as a default-mark relationship, in which the masculine is the unmarked form that absorbs the feminine.
Le garçon et la fille sont grands pour leur âge.
The boy and the girl are tall for their age. (masc. + fem. → masc. plural)
Mon père et ma mère sont fatigués après le voyage.
My father and my mother are tired after the trip. (masc. + fem. → masc. plural)
Le jardin et la cuisine sont propres.
The garden and the kitchen are clean. (masc. + fem. → masc. plural)
If both nouns are feminine, the adjective takes the feminine plural:
La porte et la fenêtre sont ouvertes.
The door and the window are open.
If both are masculine, masculine plural:
Le canapé et le fauteuil sont neufs.
The sofa and the armchair are new.
This masculine-wins rule is firmly entrenched in standard French. There is an ongoing public debate about whether to replace it with proximity agreement (the adjective agreeing with the closest noun, an older Latin pattern) or to write inclusive forms with a midpoint (grand·e·s), but both alternatives remain marginal in published writing. For now, write the traditional rule and recognize the alternatives only as a stylistic choice some writers make.
Multiple nouns sharing one adjective
When an adjective comes after two coordinated nouns and could plausibly modify either one or both, French disambiguates by agreement.
J'ai acheté des poissons et des fleurs rouges.
I bought fish and red flowers. (rouges agrees with fleurs only — the fish are not red)
J'ai acheté des poissons et des fleurs rouges.
I bought red fish and red flowers. (rouges agrees with both — both are red)
These two readings are spelled identically because poissons (m.) and fleurs (f.) share the same plural inflection on the adjective when it goes masculine plural — but if the speaker wants to pick out one noun only, they can:
J'ai acheté des poissons et des fleurs rouge.
I bought fish and red flowers. (rouge — singular — would only modify the closest noun, but this form is unusual; rephrasing is preferred)
In practice, French prefers to rephrase rather than rely on the agreement to disambiguate: J'ai acheté des poissons et des fleurs, ces dernières étant rouges. The agreement-based disambiguation works in writing but is too fragile for spoken French, where it disappears.
Compound adjectives: usually invariable
Color adjectives formed from a noun, or color adjectives modified by another adjective or a noun, are invariable — they freeze in the masculine singular form regardless of the gender or number of the noun.
J'ai trouvé des chemises bleu marine en solde.
I found navy-blue shirts on sale. (bleu marine — invariable compound)
Elle porte une robe vert pomme.
She's wearing an apple-green dress. (vert pomme — invariable)
Mes amis ont des yeux bleu clair, comme leur père.
My friends have light-blue eyes, like their father. (bleu clair — invariable)
The same rule applies to colors derived from a noun referring to an object:
Des nappes orange recouvraient les tables.
Orange tablecloths covered the tables. (orange — from the fruit; invariable)
Elle aime les fleurs cerise.
She likes cherry-colored flowers. (cerise — invariable)
Les murs sont peints en jaune citron.
The walls are painted lemon yellow.
But colors that are purely adjectival by origin do agree:
Les murs sont blancs et le sol est gris.
The walls are white and the floor is grey. (blanc / gris — agree as adjectives)
J'ai des chaussures rouges et un sac vert.
I have red shoes and a green bag.
The general principle: if the color comes from a noun (the name of a fruit, a flower, a stone, a place), it's invariable; if it has been an adjective in its own right since old French, it agrees.
Avoir l'air + adjective
The expression avoir l'air (to look, seem) is the classic agreement headache because grammatically the adjective could be agreeing with the masculine noun air or with the subject of avoir. Two analyses, two agreement patterns:
- Traditional: the adjective modifies l'air, so it stays masculine singular.
- Modern: the whole expression is felt as a copula meaning to seem, so the adjective agrees with the subject — exactly as it would after être.
Both analyses are accepted in modern French. The modern subject-agreement reading dominates in speech and is increasingly the default in writing, especially when the subject is a person.
Elle a l'air heureuse aujourd'hui.
She looks happy today. (modern — agrees with elle)
Elle a l'air heureux aujourd'hui.
She looks happy today. (traditional — agrees with l'air)
When the subject is a thing rather than a person, the traditional masculine-singular agreement still feels natural to many writers:
Cette tarte a l'air délicieux.
This pie looks delicious. (traditional, treats l'air as the head)
Cette tarte a l'air délicieuse.
This pie looks delicious. (modern subject agreement)
A common decision rule used by careful writers: when the meaning is to have an X look (literal — physical appearance), agree with l'air in the masculine. When the meaning is to seem (figurative — overall impression), agree with the subject.
Il a l'air sévère, mais en fait il est très gentil.
He looks stern, but actually he's very kind. (figurative, would also accept agreement with subject)
Cette pièce a un air mystérieux.
This room has a mysterious air. (literal — un air, with article and clearly nominal)
If you are writing for a general audience and the subject is a person, agree with the subject — that's the modern norm and the safer choice.
Demi: invariable before, agrees after
Demi (half) follows a position-dependent rule that catches out almost everyone the first time.
- Before the noun, joined by a hyphen, demi is invariable and so is the noun (no plural -s on demi).
Je voudrais une demi-baguette, s'il vous plaît.
I'd like half a baguette, please. (demi-baguette — demi invariable)
On va attendre une demi-heure de plus.
We're going to wait another half hour.
Il a fini son devoir en deux demi-heures.
He finished his homework in two half-hours. (demi still invariable; only heures pluralizes)
- After the noun, joined by et, demi agrees in gender with the noun but never in number — it always stays singular.
Il est trois heures et demie.
It's three thirty. (heure feminine → demie)
Le bébé a un an et demi.
The baby is a year and a half old. (an masculine → demi)
J'ai attendu deux heures et demie.
I waited two and a half hours. (heures fem. plural, but demie singular)
So you write deux heures et demie, never deux heures et demies.
Tout as an adverb (entirely, completely)
When tout modifies an adjective, it is functioning as an adverb meaning entirely, completely, very. As an adverb, you'd expect it to be invariable — and that is the rule for masculine adjectives. But for feminine adjectives, tout has a quirky compromise: it agrees if the adjective starts with a consonant or an aspirated h, and stays invariable if it starts with a vowel or a mute h. The reason is purely phonetic: tout in front of a vowel-initial feminine adjective sounds the same with or without the agreement, so the language opted to leave it invariable; in front of a consonant-initial feminine, the agreement adds a syllable that wakes up the consonant.
Elle est tout heureuse de te voir.
She's completely happy to see you. (heureuse begins with mute h — tout invariable)
Elles sont toutes contentes de la nouvelle.
They're (all) entirely happy about the news. (contentes begins with consonant — toutes agrees, fem. pl.)
Ces fleurs sont toutes fraîches.
These flowers are completely fresh. (fraîches begins with consonant — toutes agrees)
Elles sont tout étonnées.
They are entirely surprised. (étonnées begins with vowel — tout invariable)
Note that toutes in toutes contentes could be misread as the determiner all — but it's not the determiner here, it's the adverb that has agreed for phonetic reasons. The semantic difference: Elles sont toutes contentes (adverb) means They are all completely happy, with toutes as an intensifier; Toutes les filles sont contentes (determiner) means All the girls are happy.
Adverbs from adjectives are invariable
When an adjective is being used adverbially — modifying a verb rather than a noun — it stays in the masculine singular form, no matter what gender the subject is.
Cette voiture coûte cher.
This car costs a lot. (cher — adverb, invariable)
Ces fleurs sentent bon.
These flowers smell good. (bon — adverb, invariable)
Elle parle fort.
She speaks loudly. (fort — adverb, invariable)
Cette pomme est bonne ; elle sent bon.
This apple is good; it smells nice. (bonne adjective agrees, bon adverbial does not)
The trap is that the same word appears in both roles in the same sentence, and you have to track which is which. Bonne describes the apple (adjective, agrees); bon describes how it smells (adverb, invariable).
Phrases with a hidden second noun
When an adjective seems to modify the most recent noun but actually modifies an earlier head, agreement is determined by the head.
C'est un de ces films incroyables qu'on ne peut oublier.
It's one of those incredible films you can't forget. (films, the antecedent of qu', is the head — agrees with films)
Une bouteille de vin rouge.
A bottle of red wine. (rouge agrees with vin, not bouteille — wine is red, not the bottle)
Une bouteille de vin pleine.
A full bottle of wine. (pleine agrees with bouteille — the bottle is full, not the wine)
The placement of the adjective often clarifies which noun it modifies; when ambiguous, the agreement is your tool to disambiguate.
Invariable adjectives
A small set of adjectives never agree at all. They are mostly recent borrowings, fixed expressions, or words frozen by tradition.
Elle a des yeux marron.
She has brown eyes. (marron — borrowed from the noun; invariable)
Des sacs kaki et des chemises chocolat.
Khaki bags and chocolate-colored shirts. (kaki, chocolat — invariable)
Une chaussette orange.
An orange sock. (orange — invariable)
Mes amies sont chic, comme toujours.
My friends are stylish, as always. (chic — invariable as adjective; chics used to be wrong but is now tolerated)
Ces films sont super.
These films are great. (super — invariable colloquial adjective)
A few adjectives have one foot in each camp — snob used to be invariable but is now often written snobs in the plural; standard is generally invariable but you sometimes see standards.
Common Mistakes
❌ Le garçon et la fille sont grandes.
Incorrect — mixed gender requires masculine plural
✅ Le garçon et la fille sont grands.
The boy and the girl are tall.
❌ Une demi-heure et demie
Incorrect — demi before noun is invariable; we wouldn't say it this way anyway
✅ Une heure et demie.
An hour and a half.
❌ Elle est toute heureuse de te voir.
Incorrect — heureuse begins with mute h, tout stays invariable
✅ Elle est tout heureuse de te voir.
She's completely happy to see you.
❌ Des chemises bleues marine
Incorrect — compound color is invariable, no agreement on either part
✅ Des chemises bleu marine.
Navy-blue shirts.
❌ Cette fleur sent bonne.
Incorrect — bon used adverbially with sentir, invariable
✅ Cette fleur sent bon.
This flower smells good.
❌ Des yeux marrons
Incorrect — marron is invariable when it's a color
✅ Des yeux marron.
Brown eyes.
Key takeaways
The default rule (match the noun in gender and number) covers most situations, but a handful of corner cases require their own logic. Mixed-gender subjects take masculine plural agreement. Compound color adjectives stay invariable. Avoir l'air allows both traditional masculine-singular agreement with l'air and modern subject agreement; pick subject agreement when the meaning is to seem. Demi is invariable before the noun, agrees in gender (but not number) after the noun. The adverb tout before a feminine adjective agrees if the adjective starts with a consonant or aspirated h, and stays invariable if it starts with a vowel or mute h — a phonetic compromise. Adverbially-used adjectives are invariable. And a small group of borrowed or compound adjectives never agree at all. Keep these patterns close at hand and you will navigate the corner cases the way careful native writers do.
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