Key rules Functions Exercises

Key rules for all modals

RuleCorrectWrong
No -s in third person She can swim. ✗ She cans swim.
Followed by infinitive (no to) You must go. ✗ You must to go.
No -ing form / no past tense I must leave. → use had to for past ✗ I musted leave.
Negative: modal + not You cannot / can't park here. ✗ You not can park here.
Question: inversion only Can you help me? ✗ Do you can help me?

Functions at a glance

FunctionModalsExample
Ability can / can't · could / couldn't · be able to She can speak four languages.
Permission can · may (formal) · could (polite) · allowed to · might (extremely formal) May I leave early today?
Obligation must · have to · should · ought to* · need to You must wear a seatbelt.
Prohibition mustn't · can't · may not · not allowed to You mustn't smoke here.
No obligation don't have to · needn't You don't have to pay — it's free.
Advice should · ought to · had better You should see a doctor.
Possibility / probability might · may · could · must · should · can't It might rain later.
Request can · could (polite) · will · would (polite) Could you open the window?
Offer / suggestion shall · can · could · would Shall I carry that for you?
had better: Stronger and more urgent than should. Implies a negative consequence if you don't follow the advice: "You had better call him now — he's furious." Often shortened to you'd better.
*ought to: Expresses what is the right thing to do, what you should do according to rules, duty, fairness, or good practice. It's weaker than must / have to, but stronger than just a suggestion.

Exercises

EXERCISE:

Warm-up — Choose the correct modal

Choose the correct modal for each situation.

1. You want to ask permission politely in a formal situation.

2. Something is forbidden — it is not allowed.

3. You want to make a polite request.

4. You want to offer help: "___ I carry your bags?"

← Second Conditional Modals: Ability →