Modals

Level B1 · Modals

Modals add meaning to a main verb — ability, permission, obligation, possibility, or advice — rather than describing an action on their own. The tricky part: the same modal often carries different meanings depending on context, so can means both ability (I can swim) and permission (you can leave now).

Form: modal + base verb, always — never add -s, -ing, or -ed to the modal, and never use to after it: she can swim, not she cans swim or she can to swim. One form covers every subject, and negatives/questions never use do: I can't swim (not I don't can swim), can you swim? (not do you can swim?).

The core modals, grouped by what they express:

• can / could — ability and permission: I can swim; could you help me? (could is also more polite/tentative)
• must / have to — obligation: you must wear a seatbelt; I have to finish this by Friday (have to often sounds like an outside rule, must like the speaker's own judgment)
• should — advice or a mild recommendation: you should see a doctor
• may / might — possibility: it may rain later; she might be at home (might is slightly less certain than may)
• must / can't — deduction, a near-certain conclusion from evidence: he must be asleep (positive); that can't be her car (negative) — not obligation here, just 'this is surely true.'

The most common mistake is treating a modal like a normal verb: adding -s (she cans drive), adding to after it (she must to go), or adding do in questions and negatives (does she can drive?). A true modal never changes form and never needs do — she can drive, does she have to go? (have to is the exception: it isn't a true modal, so it behaves like a normal verb and does use do).

Some modals do have past forms (could ← can, would ← will, might ← may), but must doesn't — use had to for past obligation. And could only works for general past ability (I could swim for hours as a child); a specific one-time success needs was able to or managed to (she managed to finish her homework yesterday, not she could finish it).

Practice

Ability, Permission & Obligation · Advice, Possibility, Deduction & Past