Modal Verbs: can, must, should, might...

Intermediate · Modal Verbs

Modal verbs are helper verbs that add a layer of meaning to another verb — ability, permission, obligation, possibility, or advice. They are special because they never change form (no -s, no -ed) and are always followed by the base verb with no "to".

One modal can express several ideas depending on context, and small changes can make you sound polite or rude, so they are worth practising carefully.

How to build it

subject + modal + base verb (e.g. She can swim / You must go / We should wait)

Rules & examples

Ability: can (present) / could (past).
What you are or were able to do.
- I can swim.
- She could read at age four.
Permission & requests: can, could, may.
"Could" and "may" are more polite/formal than "can".
- Can I leave early?
- Could you help me?
- May I come in?
Obligation & necessity: must, have to.
"Must" often = a personal or rule-based duty; "have to" = an external necessity.
- You must wear a seatbelt.
- I have to work tomorrow.
Advice: should, ought to, had better.
"Had better" is a stronger warning than "should".
- You should see a doctor.
- You'd better hurry or we'll miss the train.
Possibility: may, might, could.
Something is possible but not certain.
- It might rain later.
- She may be at home.
Prohibition vs. no obligation: "mustn't" (forbidden) vs. "don't have to" (optional).
These two are easy to confuse but are opposites.
- You mustn't smoke here. (it's forbidden)
- You don't have to come. (it's your choice)

Tips to remember

Modals take the base verb with no "to": "must go", never "must to go".
"can" has no future form — use "will be able to": "I will be able to help tomorrow."

Common mistakes

✗ You must to go now. → ✓ You must go now. — Modals are followed by the base verb, never "to".
✗ You mustn't pay; it's free. → ✓ You don't have to pay; it's free. — "Mustn't" means forbidden; "don't have to" means not necessary.