Grammar Exceptions
French grammar loves a good exception. Here are a few that trip up learners at every level — worth getting comfortable with early.
"Être" and "avoir" in the passé composé
Most verbs use "avoir" as their auxiliary in the past tense, but roughly 15 verbs of movement/state (aller, venir, naître, mourir, monter, descendre...) use "être" instead — and their past participle must agree in gender/number with the subject.
"Elle est allée" (not "elle a allé") — She went.
Irregular plurals in -al → -aux
Most nouns just add "-s" for the plural, but nouns ending in "-al" usually change to "-aux" instead — with a handful of stubborn exceptions that just add "-s" like everyone else.
"un cheval" → "des chevaux" (horses), but "un bal" → "des bals" (dances).
"Tout" changes form more than you'd expect
"Tout" agrees in gender and number (tout, toute, tous, toutes) as an adjective, but stays invariable as an adverb before most adjectives — except before a feminine adjective starting with a consonant, where it agrees again.
"Elle est toute contente" (adverb, agrees) vs. "Elle est tout étonnée" (adverb, no agreement before a vowel).
Silent letters that aren't actually silent
French famously drops final consonants, but liaison brings some of them back to life when the next word starts with a vowel — and a few words break the liaison rule entirely ("les haricots" is never linked).
"les amis" is pronounced "lez‑ami", but "les haricots" keeps a hard break.
The subjunctive shows up in surprisingly ordinary sentences
Learners expect the subjunctive only after emotion or doubt, but a long list of everyday expressions ("il faut que", "bien que", "avant que") quietly require it too, with no exceptions.
"Il faut que tu viennes" (not "tu viens") — You need to come.
"Après-midi" doesn't pick a gender
A small set of French nouns are officially both masculine and feminine depending on usage — "après-midi" is the most common one you'll actually hit in conversation.
"un après-midi" and "une après-midi" are both correct.
"Œil" and "ciel": plurals that change root entirely
Most irregular plurals just tweak the ending, but a few nouns change almost completely in the plural — unrelated to the "-al" pattern covered above.
"un œil" → "des yeux" (eye → eyes); "un ciel" → "des cieux" (sky, poetic sense — "des ciels" also exists for the more literal, painterly sense).
Adjectives that change almost entirely in the feminine
Most adjectives just add an "-e" for the feminine form, but a handful change almost completely instead — inherited straight from Latin rather than from a regular pattern.
"beau" → "belle" (beautiful), "vieux" → "vieille" (old), "blanc" → "blanche" (white), "roux" → "rousse" (red-haired).
"Bijou, chou, genou...": plurals in -x instead of -s
Nouns ending in "-ou" normally take an "-s" in the plural, but seven of them take an "-x" instead — a closed list to just memorize, with no obvious logic to guess it from.
"un bijou" → "des bijoux" (jewels), "un chou" → "des choux" (cabbages), but "un trou" → "des trous" (holes, the regular pattern).
"Gens" changes gender depending on the adjective's position
"Gens" (people) is a masculine plural noun, except for an adjective placed right before it, which then goes feminine — one of the strangest agreement rules in French, even for native speakers.
"de vieilles gens" (adjective before, feminine) but "des gens vieux" (adjective after, masculine) — both mean "old people".
"Malgré que" is technically wrong — but almost everyone uses it
Grammar guides prescribe "bien que" or "quoique" for concession; "malgré que" remains officially incorrect ("malgré" is a preposition, not a conjunction), yet you'll hear it constantly in speech.
Correct form: "bien qu'il pleuve, je sors." Very common but technically wrong: "malgré qu'il pleuve, je sors." — both mean "although it's raining, I'm going out".
Compound noun plurals aren't always what you'd expect
In a compound noun, only the nouns and adjectives take the plural marker — never verbs or prepositions, which produces plurals that look irregular at first glance.
"un compte-gouttes" → "des compte-gouttes" (compte is a verb form, stays unchanged); "un grand-père" → "des grands-pères" (both parts agree, grandfather/grandfathers).
"Demi" is invariable before the noun, but agrees after it
Placed before the noun and joined with a hyphen, "demi" (half) never agrees; placed after and joined with "et", it agrees in gender (never in number, since there's always just one half).
"une demi-heure" (invariable, before) but "une heure et demie" (agrees in the feminine, after) — both mean "half an hour".
The future tense of "envoyer" doesn't follow the expected pattern
"-oyer" verbs normally change the "y" to an "i" in the future ("nettoyer" → "je nettoierai"), but "envoyer" (to send) goes further and becomes "enverrai" — an irregular stem inherited from Old French.
"j'enverrai", "tu enverras"... (not "j'envoierai", even though that would seem more logical).