The short version

• Devoir = must/have to, a PERSONAL obligation, conjugated for whoever has it (je dois, tu dois, il doit…).
• Falloir = it is necessary, an IMPERSONAL obligation, existing only as il faut, with no other conjugated forms.

If you’re naming who specifically has the obligation, use devoir and conjugate it to match them. If you’re stating a general necessity without pinning it on anyone in particular, use il faut.

When to use devoir

• Personal obligation: Je dois partir maintenant. (I have to leave now.)
• Conjugated for the subject: Tu dois étudier. (You must study.) Ils doivent attendre. (They have to wait.)
• Probability, a secondary use: Il doit être fatigué. (He must be tired — a guess.)
• Debt, a separate literal meaning: Je te dois dix euros. (I owe you ten euros.)
• Past obligation: J’ai dû partir tôt. (I had to leave early.)

When to use falloir

• General necessity: Il faut partir. (One has to leave. / We need to leave.)
• With a specific person via an indirect object pronoun: Il me faut du temps. (I need time.)
• Followed by a subjunctive clause for a specific person’s obligation: Il faut que tu partes. (You need to leave.)
• Never conjugated for a subject other than the impersonal il — there’s no je faux or tu faux.
• In other tenses, still impersonal: Il fallait partir plus tôt. (We should have left earlier.)

Quick chart

Two ways to make falloir personal without conjugating it

Because falloir can never conjugate to match a specific subject, French needs two workarounds to attach a general necessity to a particular person, and both are worth knowing. The first is adding an indirect object pronoun directly to il faut: il me faut du temps literally means “time is necessary to me,” using me the same way you’d use it with plaire or manquer — this structure feels backwards to English speakers but works exactly like j’ai besoin de in meaning, just grammatically inverted. The second workaround is following il faut with que and a subjunctive clause: il faut que je parte (“it’s necessary that I leave,” i.e., “I have to leave”) lets you specify exactly who the obligation belongs to, using the subjunctive mood inside the que-clause. Both structures accomplish roughly what devoir does directly, but neither actually conjugates falloir itself — the verb stays locked in its single impersonal il faut form no matter which person the obligation ultimately lands on, even across different tenses like il fallait (had to) or il faudra (will have to).

Mistakes learners make

• Trying to conjugate falloir for a subject other than il — there’s no such thing as tu faux or je faux; the verb only exists as il faut.
• Using devoir when a general, unattributed necessity is meant, producing an overly personal statement where il faut would sound more natural.
• Forgetting the subjunctive after il faut que — it’s il faut que tu partes, not il faut que tu pars.
• Confusing devoir’s obligation meaning with its “probability” meaning (il doit être tard = it must be late, a guess) versus its “owe” meaning (je lui dois de l’argent).
• Forgetting falloir still changes tense (il fallait, il faudra) even though it never changes person.

Frequently asked questions

What’s the difference between devoir and falloir?

Devoir is a personal obligation verb, conjugated for whoever has to do something. Falloir is impersonal and only exists as il faut, expressing a general necessity without naming a specific person directly.

Can you conjugate falloir for je or tu?

No. Falloir only exists in the impersonal third-person form il faut — there’s no je faux or tu faux. To attach it to a specific person, you add an indirect object pronoun (il me faut) or use il faut que + subjunctive.

How do you say “I have to leave” in French two different ways?

Je dois partir (using devoir, personal) or il faut que je parte (using falloir with a subjunctive clause) — both mean roughly the same thing, built differently.

What does il me faut mean?

“I need,” literally “it is necessary to me.” It’s falloir’s way of attaching a general necessity to a specific person without conjugating the verb itself.

Does devoir always mean obligation?

No. Devoir can also express probability (il doit être tard — it must be late, a guess) or literal debt (je te dois vingt euros — I owe you twenty euros).

Why does il faut que take the subjunctive?

Because il faut que is a necessity expression, and necessity is one of the standard categories of French subjunctive triggers, alongside wishes, emotion, and doubt.

Is il faut more formal than devoir?

Not exactly formal versus informal — il faut is simply the impersonal option, common in both speech and writing whenever you’re stating a general rule rather than a specific person’s obligation.

Does falloir change in the future or conditional?

Yes, but only in tense, never in person: il faudra (it will be necessary) and il faudrait (it would be necessary) both stay locked to the impersonal il.

Devoir and falloir look similar in meaning but behave completely differently in structure. corrector.co’s free French checker flags falloir conjugated incorrectly for a subject other than il.

Next: French Subjunctive Triggers · Y vs En