sûr/sur, dû/du, mûr/mur (the distinguishing circumflex)

Summary

Several French homophone pairs are distinguished only by a circumflex accent: sûr ("sure/certain", adjective, agrees: sûre/sûrs) vs sur ("on", invariable preposition); dû (past participle of devoir, circumflex only in the masculine singular: due/dus/dues drop it) vs du (partitive/contracted article); mûr ("ripe/mature", agrees: mûre) vs mur ("wall", noun). The same pattern appears in jeûne ("fast", noun/verb) vs jeune ("young") and crû (past participle of croître) vs cru (past participle of croire, or "raw"). Rule of thumb: the circumflex marks the meaningful word (adjective/participle); the bare form is the grammatical word (preposition/article/noun).

Explanation

French has a small family of homophone pairs where the only written difference is a circumflex accent (^), and where losing or misplacing that accent changes the word's grammatical identity rather than just its pronunciation nuance. The three best-known pairs are sûr/sur, dû/du, and mûr/mur; the same underlying pattern also shows up in jeûne/jeune and crû/cru.

Sûr, with the circumflex, is an adjective meaning "sure," "certain," or "safe," and like any adjective it agrees in gender and number: sûr, sûre, sûrs, sûres (je suis sûr de moi, elle est sûre d'elle, un endroit sûr). Sur, without any accent, is an invariable preposition meaning "on" (le livre est sur la table). Because sur is a preposition, it never changes form and is always followed by a noun phrase indicating a surface or topic; sûr, being an adjective, always agrees with whatever it describes and typically follows être or a noun.

Dû, with the circumflex, is the masculine singular form of the past participle of devoir ("to have to" / "to owe"): j'ai dû partir ("I had to leave"), la somme due (feminine, no circumflex) — this is the crucial detail: the circumflex on dû appears only in the masculine singular; the feminine due and the plurals dus/dues all lose it. Du, without an accent, is either the partitive article (du pain, "some bread") or the contraction of de + le (il vient du bureau, "he's coming from the office"). The test is grammatical function: if the word is a verb form completing an auxiliary avoir, it is dû (or one of its accent-free agreement forms); if it introduces a noun in a partitive or contracted sense, it is du.

Mûr, with the circumflex, is an adjective meaning "ripe" (of fruit) or "mature" (of a person or plan), and it agrees like any adjective: mûr, mûre, mûrs, mûres (une pêche mûre, un projet mûr). Mur, without an accent, is simply the noun "a wall" (un mur, les murs de la ville). Here the test is part of speech: does the word describe something (adjective, needs agreement) or name a physical object (noun, takes an article)?

The same logic extends to two rarer but instructive pairs. Jeûne (circumflex) is the noun or verb form related to fasting (le jeûne, "the fast"; je jeûne, "I fast"), while jeune (no circumflex) is the common adjective "young" (un jeune homme). Crû (circumflex, agrees: crue/crus/crues) is the past participle of croître ("to grow/increase": les prix ont crû), while cru (no circumflex) is either the past participle of croire ("to believe": j'ai cru que tu venais) or an adjective meaning "raw" (de la viande crue) — note that cru itself is ambiguous between two meanings, both without a circumflex, so context alone resolves it.

The rule of thumb that ties all these pairs together: the circumflex marks the word that carries independent meaning and inflects to show it — an adjective that agrees, or a participle tied to a specific verb — while the accent-free twin is the small grammatical workhorse: a preposition, an article, or a plain noun. When in doubt, check whether the word agrees in gender/number (circumflex family) or stays frozen while acting as a functional glue-word (no accent).

Examples

Je suis sûr que le livre est sur la table. — I'm sure the book is on the table. (sûr: adjective "sure" (agrees); sur: invariable preposition "on".)

J'ai dû annuler à cause du mauvais temps. — I had to cancel because of the bad weather. (dû: past participle of devoir, masculine singular; du: contraction de + le.)

La somme due sera versée après la réunion. — The amount owed will be paid after the meeting. (due: feminine of dû (devoir), circumflex disappears when it agrees.)

Cette pêche est bien mûre, pose-la sur le mur du jardin. — This peach is nice and ripe; put it on the garden wall. (mûre: adjective "ripe" (agrees); mur: noun "wall".)

Après le jeûne, il a mangé un jeune poulet avec de la viande crue en garniture. — After the fast, he ate a young chicken with raw meat as a side. (jeûne: noun "fast" (circumflex) vs jeune: adjective "young" (no accent); cru(e) here means "raw.")

Common mistakes

Related rules

• Past-participle agreement with avoir (preceding direct object)
• Partitive articles (du / de la / des)
• Article contractions (au / aux / du / des)
• Accents (é è ê ç)