Modal verbs express a relationship between the subject and the action, such as obligation, ability, permission, willingness, or probability. They often introduce an additional meaning that clarifies whether one must act, whether one can act, whether one wants to act, or whether the action is only contemplated. To understand their role, they should also be linked to the [Verb Moods], because they organize the value of the utterance as well as the time of the action.

Obligation is expressed with devoir, falloir, avoir à and être obligé de. Devoir marks a more direct obligation, while falloir is impersonal with il faut and presents a general necessity. In a more polite register, the conditional softens the obligation, as in vous devriez, which aligns with the use of the [Conditional].

IdéeIdea	ExempleExample
Devoir exprime une obligation directe.Devoir expresses a direct obligation.	Tu dois partir maintenant.You must leave now.
Falloir exprime une nécessité impersonnelle.Falloir expresses an impersonal necessity.	Il faut répondre avant midi.It is necessary to respond before noon.
Avoir à exprime une contrainte ou une tâche.Avoir à expresses a constraint or a task.	J ai à finir ce dossier.I have to finish this file.
Être obligé de exprime une obligation forte.Être obligé de expresses a strong obligation.	Nous sommes obligés de changer de train.We are obliged to change trains.
Le conditionnel adoucit l obligation.The conditional softens the obligation.	Vous devriez demander confirmation.You should ask for confirmation.

Capacity is expressed with pouvoir, savoir faire and être capable de. Pouvoir indicates that an action is possible, savoir faire emphasizes a learned skill, and être capable de underscores the actual ability of a person or thing. This distinction is useful with the [Regular Verbs] and the [Irregular Verbs], because the form of the main verb varies according to the subject and the tense.

IdéeIdea	ExempleExample
Pouvoir exprime une possibilité ou une capacité.Pouvoir expresses a possibility or a capability.	Je peux courir plus vite.I can run faster.
Savoir faire exprime une compétence apprise.Savoir faire expresses a learned skill.	Elle sait réparer un vélo.She knows how to repair a bicycle.
Être capable de exprime une aptitude réelle.Être capable de expresses a real aptitude.	Ils sont capables de terminer seuls.They are able to finish on their own.
La capacité peut être physique ou circonstancielle.The ability can be physical or situational.	Je ne peux pas venir aujourd hui.I can't come today.

Permission is expressed with pouvoir, laisser, permettre and autoriser. Pouvoir indicates that an action is allowed, while laisser, permettre and autoriser show authorization given by someone or by a rule. This value is common with the [Auxiliary Verbs] and with the polite forms of requests.

IdéeIdea	ExempleExample
Pouvoir exprime une permission.Pouvoir expresses permission.	Vous pouvez entrer.You may enter.
Laisser exprime qu on ne s oppose pas à l action.Laisser expresses that one does not oppose the action.	Je te laisse parler.I'll let you speak.
Permettre exprime une autorisation officielle ou pratique.Permettre expresses an official or practical authorization.	Le règlement permet de sortir.The regulation allows you to go out.
Autoriser exprime un accord explicite.Autoriser expresses explicit agreement.	Le chef autorise le départ.The boss authorizes the departure.

Will is expressed with vouloir, souhaiter and préférer followed by the infinitive. Vouloir marks a strong intention, souhaiter conveys a more formal or softer nuance, and préférer indicates a choice among several possibilities. For the verbal structure, the infinitive remains the most common form after these verbs, which is also observed with the [Imperative] when a will becomes an order or directive.

IdéeIdea	ExempleExample
Vouloir exprime une intention.Vouloir expresses an intention.	Je veux partir tôt.I want to leave early.
Souhaiter exprime une volonté plus polie.Souhaiter expresses a more polite will.	Nous souhaitons obtenir une réponse.We would like to obtain a response.
Préférer exprime un choix net.Préférer expresses a definite choice.	Elle préfère rester ici.She prefers to stay here.
Ces verbes sont suivis de l infinitif.These verbs are followed by the infinitive.	Je veux apprendre vite.I want to learn quickly.

Probability or possibility is expressed with il se peut, pouvoir in the sense of possibility, and devoir in the sense of probability. Il se peut presents a fact as uncertain, pouvoir signals that something is feasible, and devoir may indicate strong likelihood rather than obligation. This value depends on context and should not be confused with strict necessity.

IdéeIdea	ExempleExample
Il se peut marque l incertitude.Il se peut marks uncertainty.	Il se peut qu il arrive en retard.It may arrive late.
Pouvoir marque une possibilité.Pouvoir marks a possibility.	Cette clé peut ouvrir la porte.This key can open the door.
Devoir marque une probabilité forte.Devoir marks a strong probability.	Il doit être déjà parti.He must have left already.
Le contexte distingue probabilité et obligation.Context distinguishes probability and obligation.	Il doit venir peut être demain.He may come tomorrow.

Modal verbs are built in several tenses, but the most frequent present forms are essential to memorize. Pouvoir yields je peux, il peut and nous pouvons; devoir yields je dois and nous devons; vouloir yields je veux and nous voulons; et savoir yields je sais. Falloir remains impersonal with il faut, and its personal use remains marginal in common usage. The passé composé of pouvoir is j ai pu, which allows talking about a completed ability or permission.

SujetSubject	VerbeVerb	ExempleExample
JeI	peuxcan	Je peux, si j ai le tempsI can, if I have time
IlIt	peutcan	Il peut, quand la porte est ouverteIt can, when the door is open
NousWe	pouvonscan	Nous pouvons, si le train arriveWe can, if the train arrives
JeI	doismust	Je dois, parce que c est urgentI must, because it is urgent
NousWe	devonsmust	Nous devons, car le délai est courtWe must, because the deadline is short
JeI	veuxwant	Je veux, avant la réunionI want, before the meeting
NousWe	voulonswant	Nous voulons, pour avancer ensembleWe want, to move forward together
JeI	saisknow	Je sais, après l entraînementI know, after the training
IlIt	fautis needed	Il faut, pour respecter la règleIt is needed, to respect the rule
JI	ai puhave been able to	J ai pu, grâce à l aide reçueI have been able to, thanks to the help received

The choice of the modal depends on the modality to express and not only on the time of the action. When the main idea is obligation, capacity, permission or probability, a modal verb is the best starting point; when the idea is more nuanced, register and context decide between devoir, pouvoir, vouloir or falloir. Politeness, the strength of constraint and the speaker's intention guide this choice, as in the usages studied with the [Subjunctive] and the other verbal values.