Modal Verbs: Can, Could, Must, Should

Modal verbs are helping verbs that express ability, possibility, necessity, or advice. They are followed by the base form of the verb (no -s, no to).

Can / Could

- Can = present ability: I can swim. - Could = past ability or polite requests: I could swim when I was five. / Could you help me?

Must

- Must = strong obligation: You must wear a seatbelt. - Must not = prohibition: You must not smoke here.

Should

- Should = advice or recommendation: You should drink more water. - Shouldn't = advice against: You shouldn't eat so much sugar.

Key rules

- Never add -s to modals (never he cans) - Never use two modals together (never he will can) - The verb after a modal is always in base form