French has three ways to turn a statement into a yes/no question, from casual to formal, and a set of question words for everything else (who, what, where...).
1. Yes/no questions: three ways to ask
| Intonation (casual, spoken) | Tu aimes le café ? |
| Est-ce que (most common, any register) | Est-ce que tu aimes le café ? |
| Inversion (formal, written) | Aimes-tu le café ? |
All three mean the same thing: "Do you like coffee?" Intonation just raises your voice at the end of a normal statement; est-ce que adds a fixed phrase to the front with no word-order change; inversion swaps the verb and subject, joined by a hyphen.
2. Watch out: the euphonic "-t-"
With inversion, when the verb form ends in a vowel letter (-e or -a) and the subject is il, elle, or on, French inserts -t- between them so two vowel sounds don't collide.
| Il parle français. | Parle-t-il français ? |
| Elle a un chat. | A-t-elle un chat ? |
| On va au cinéma. | Va-t-on au cinéma ? |
No -t- needed when the verb already ends in a consonant sound, or with tu, nous, vous, ils/elles: Fais-tu, Avez-vous, Sont-ils. Compare il parle (needs -t-) with il part (already ends in a consonant, part-il ?, no -t- needed).
3. Asking for information: question words
| qui | who |
| que / quoi | what |
| où | where |
| quand | when |
| comment | how |
| pourquoi | why |
| combien | how much, how many |
| quel / quelle / quels / quelles | which, what (agrees with the noun) |
4. Combining a question word with est-ce que or inversion
| Où est-ce que tu habites ? | Where do you live? |
| Où habites-tu ? | Where do you live? (more formal) |
| Qu'est-ce que c'est ? | What is it? |
| Pourquoi es-tu en retard ? | Why are you late? |
Quel/quelle/quels/quelles is an adjective, it agrees with the noun right after it: Quel âge as-tu ? (age is masc.), Quelle heure est-il ? (heure is fem.).
5. Quick reference
| Intonation | Tu viens ?, same word order as a statement |
| Est-ce que | Est-ce que tu viens ?, no word-order change |
| Inversion | Viens-tu ?, verb-subject, add -t- for il/elle/on + vowel ending |
| Question words | qui, que, où, quand, comment, pourquoi, combien, quel |