French has a quirk that trips up learners and native speakers alike: a huge number of common words are pronounced exactly the same but spelled completely differently, with completely different meanings. Linguists call these homophones, and in French they're not a rare curiosity, they're everywhere, in nearly every sentence you write.
The good news: you don't need to "just know" each one by memory. There's a simple substitution test for almost every pair that tells you, in about two seconds, which spelling you need. Here are the eight pairs my students mix up most, and the trick that fixes each one for good.
Why homophones matter more than they seem to
When you're speaking, homophones don't matter at all, they sound identical, so nobody notices. The problem shows up entirely in writing: emails, texts, and especially exams. DELF and DALF written production sections penalise exactly these mistakes, because from a French reader's perspective, mixing up à and a reads the way mixing up "there" and "their" reads in English: a small slip that stands out immediately and undermines otherwise strong writing.
The universal method: the substitution test
For almost every pair below, the trick is the same: try replacing the word with a different tense or a synonym. If the replacement still makes sense, you've found your word. If it sounds absurd, it's the other one. You don't need to memorise a rule for each pair individually, just this one method, applied eight different ways.
1. À vs A
A is the verb avoir conjugated for il/elle (has). À is a preposition (to, at, in) that never changes form.
The test: replace it with avait (imparfait of avoir). If that still works, write a. If it doesn't, write à.
Elle a un chat. → Elle avait un chat. ✓ → keep "a"
Elle va à Paris. → Elle va avait Paris. ✗ → use "à"
2. Et vs Est
Est is the verb être conjugated for il/elle (is). Et is a conjunction meaning "and."
The test: replace it with était (imparfait of être). If that works, write est. If not, write et.
Il est fatigué. → Il était fatigué. ✓ → keep "est"
Paul et Marie. → Paul était Marie. ✗ → use "et"
3. On vs Ont
Ont is the verb avoir conjugated for ils/elles (have). On is a subject pronoun meaning "we" (informal) or "one/people."
The test: replace it with avaient. If that works, write ont. If not (try replacing with il instead: if that works, it's a pronoun), write on.
Ils ont fini. → Ils avaient fini. ✓ → keep "ont"
On mange à midi. → Il mange à midi. ✓ (pronoun test) → use "on"
4. Son vs Sont
Sont is the verb être conjugated for ils/elles (are). Son is a possessive adjective (his/her), always followed by a masculine or vowel-starting noun.
The test: replace it with étaient. If that works, write sont. If not, write son.
Elles sont arrivées. → Elles étaient arrivées. ✓ → keep "sont"
Il cherche son livre. → Il cherche étaient livre. ✗ → use "son"
5. Ces vs Ses
Ces is a demonstrative adjective (these/those), pointing at something. Ses is a possessive adjective (his/her, plural), showing ownership.
The test: if you can add "-là" after the noun and it still makes sense (pointing at something), it's ces. If the sentence is really about who owns the thing, it's ses.
Regarde ces chaussures ! → Regarde ces chaussures-là ! ✓ → keep "ces"
Il a perdu ses clés. → (his own keys, ownership) → use "ses"
6. Sa vs Ça
Sa is a possessive adjective (his/her), always directly followed by a feminine singular noun. Ça is a pronoun meaning "that/it," and stands on its own.
The test: is there a noun immediately after it that's being "owned" by someone? Then it's sa. Does the word stand alone, replaceable by "cela"? Then it's ça.
Il aime sa voiture. → (his car, followed by a noun) → use "sa"
Ça me plaît. → Cela me plaît. ✓ → keep "ça"
7. Ou vs Où
Ou (no accent) means "or," offering a choice. Où (with accent) means "where," referring to a place or a moment in time.
The test: replace it with ou bien (or else). If that works, write ou. If the sentence is really asking about a location, write où.
Tu préfères le thé ou le café ? → …thé ou bien le café ? ✓ → keep "ou"
Où habites-tu ? → (asking for a place) → use "où"
8. Ce vs Se
Ce is a demonstrative (this/that), usually appearing before a noun or before "est." Se is a reflexive pronoun, appearing directly before a verb in pronominal constructions (se lever, se laver, s'appeler).
The test: is the word immediately followed by a verb, describing something the subject does to themselves? Then it's se. Is it pointing at a noun or introducing "c'est"? Then it's ce.
Ce livre est intéressant. → (pointing at "livre") → use "ce"
Il se lève tôt. → (reflexive, before a verb) → use "se"
All eight pairs, at a glance
| Pair | Quick test |
|---|---|
| à / a | Replace with "avait": works → a. Doesn't → à. |
| et / est | Replace with "était": works → est. Doesn't → et. |
| on / ont | Replace with "avaient": works → ont. Replace with "il": works → on. |
| son / sont | Replace with "étaient": works → sont. Doesn't → son. |
| ces / ses | Add "-là" and it still works → ces. About ownership → ses. |
| sa / ça | Followed by a noun (ownership) → sa. Stands alone, = "cela" → ça. |
| ou / où | Replace with "ou bien": works → ou. About a place → où. |
| ce / se | Before a verb, reflexive → se. Points at a noun or "c'est" → ce. |
Practice sentences to try right now
Choose the correct spelling:
- Elle (a / à) invité tous (ses / ces) amis (à / a) sa fête.
- (On / Ont) ne sait jamais (ou / où) (ce / se) trouve la sortie.
- Marie (et / est) Paul (son / sont) partis (ce / se) matin.
- (Sa / Ça) ne (se / ce) fait pas de parler comme (ça / sa).
Answers: 1. Elle a invité tous ses amis à sa fête. 2. On ne sait jamais où se trouve la sortie. 3. Marie et Paul sont partis ce matin. 4. Ça ne se fait pas de parler comme ça.
Why this is worth mastering
None of these mistakes will stop someone from understanding you when you speak. But in writing, especially for the DELF, DALF, a professional email, or a job application in French, they're exactly the kind of small, repeated error that makes otherwise fluent writing look careless. Once the substitution test becomes automatic, you'll catch these mistakes before you even finish typing the sentence.