Modal verbs (also called modal auxiliaries) are helping verbs such as can, could, may, might, must, shall, should, will, and would. They combine with the base form of a main verb, without "to", to express meanings like ability, possibility, permission, obligation, or advice.
What Is a Modal Verb?
Modal verbs are a special category of auxiliary verb. Unlike ordinary verbs, they never change form for person (no "-s" for he/she/it), are always followed by the base form of the main verb without "to" (except semi-modals like "have to" and "need to"), and form negatives and questions without "do" ("You must not go", "Can you help?").
Different modals express different meanings, and the same modal can carry more than one meaning depending on context. Can/could express ability ("She can swim") or permission ("Can I leave early?"). May/might express possibility ("It might rain"). Must/have to express obligation or strong necessity ("You must wear a seatbelt"), while mustn't expresses prohibition. Should/ought to express advice or recommendation ("You should see a doctor"). Will/shall express future predictions, promises, or offers.
Modal verbs also have past forms used for reported speech, hypothetical situations, and deductions about the past: "must have + past participle" for a confident guess about the past ("She must have left already"), and "should have + past participle" for a missed obligation or regret ("You should have told me"). Reference grammars such as the Cambridge Grammar guide document modal verb usage in detail.
Examples
| Example | Notes |
|---|---|
| She can speak three languages. | Ability |
| You must wear a helmet on this site. | Obligation |
| It might rain later today. | Possibility |
| You should apologise to her. | Advice |
| He must have forgotten the meeting. | Deduction about the past |
Related Grammar Terms
Practise Modal Verbs
Frequently Asked Questions
What are modal verbs?
Modal verbs are auxiliary verbs such as can, could, may, might, must, shall, should, will, and would, used with a main verb to express ability, possibility, permission, obligation, or advice.
How do modal verbs behave differently from ordinary verbs?
Modal verbs never add "-s" for third person singular, are followed by the base form of the main verb without "to", and form negatives/questions without "do": "She can swim", "Can she swim?", "She cannot swim."
What is the difference between can and could?
"Can" expresses present ability or permission ("I can drive"). "Could" expresses past ability ("I could swim at age five"), a more polite request ("Could you help me?"), or possibility ("It could rain").
What is the difference between must and have to?
Both express obligation, but "must" often expresses the speaker's own authority or strong personal feeling ("I must finish this today"), while "have to" often expresses an external rule or requirement ("I have to wear a uniform at work").
What does mustn't mean compared to don't have to?
"Mustn't" means it is prohibited — you are not allowed to do it ("You mustn't smoke here"). "Don't have to" means it is not necessary, but it is allowed ("You don't have to come if you're busy").
How do you talk about past possibility or deduction?
Use modal + have + past participle: "must have" for a confident guess ("She must have left"), "might have" for a weaker possibility ("He might have missed the bus"), and "can't have" for something you believe is impossible.
What is the difference between should and must?
"Should" expresses advice or a recommendation that is not compulsory ("You should exercise more"). "Must" expresses a strong obligation or rule ("You must wear a seatbelt").
Can two modal verbs be used together?
Standard English does not combine two modals together (e.g., "will can"). Instead, semi-modal substitutes are used: "will be able to" instead of "will can".
What are semi-modal verbs?
Semi-modals like "have to", "need to", and "be able to" function similarly to modal verbs but behave more like ordinary verbs — they can change form and use "do" in questions and negatives.
How can I practise modal verbs?
Try LexFizz's modal verbs exercises, which cover can, could, must, should, might, may, and more with interactive practice on meaning and form.