Modal Verbs (can, could, must)
Modal verbs are auxiliary verbs that express ability, permission, obligation, or possibility. 'Can' expresses present ability or permission. 'Could' expresses past ability or polite requests. 'Must' expresses strong obligation or logical certainty. Modal verbs are always followed by the base form of the verb.
WHEN TO USE
Use 'can' for ability/permission in the present. Use 'could' for past ability, polite requests, or possibility. Use 'must' for strong obligation (from speaker) or logical deduction. Use 'should' for advice or recommendation.
STRUCTURE
S + modal verb + base verb (no 'to')She can speak four languages.
S + modal + not + base verbYou must not park here.
Modal + S + base verb?Could you pass the salt, please?
SIGNAL WORDS
- can
- could
- must
- should
- may
- might
- will
- would
- shall
- need to
EXAMPLES
She can speak four languages fluently.
Could you please pass the salt?
You must wear a seatbelt in the car.
You should see a doctor about that cough.
He might be late — the traffic is terrible.
COMMON MISTAKES
She can to speak English.
She can speak English.
Modal verbs are followed by the base verb WITHOUT 'to'
He musts leave now.
He must leave now.
Modal verbs never add -s/-es for he/she/it
Tip
Modal verbs have TWO special rules: 1) Never add -s for he/she/it (she can, NOT she cans). 2) Always follow with a base verb, never 'to + verb' (you must go, NOT you must to go).