- Know the general rules of modal verbs: no -s, no to
- Express ability, permission and requests with can and could
- Understand the difference between must, have to, mustn't and don't have to
- Give advice with should
Look at the school rules: Students must wear a uniform. You mustn't use your phone in class. A doctor says: You should drink more water. A friend asks: Can you help me? All these sentences contain special verbs — modal verbs. They don't describe the action itself but our attitude to it: ability, obligation, permission, advice.
How modal verbs work
- The same form for all persons — no -s in the third person: she can, not she cans.
- The next verb has no to: can swim, should go.
- Add not for the negative: can't (cannot), mustn't, shouldn't.
- In questions the modal goes before the subject: Can you swim? Should I call her?
- The exception — have to: it works like an ordinary verb: she has to, I don't have to, Do you have to …?
Can and could
| Meaning | Examples |
|---|---|
| Ability | I can swim. She can't drive. |
| Permission | Can I use your phone? You can go now. |
| Requests (could is more polite) | Can you help me? Could you open the door, please? |
| Past ability | I could read when I was five. |
Must and have to
Must and have to both express obligation. Must usually shows the speaker's own feeling, or rules and written instructions: I must study harder. Have to shows obligation that comes from outside — rules, timetables, circumstances: I have to get up at 6 because school starts at 7:30. In everyday speech, have to is more common.
| Form | Meaning | Example |
|---|---|---|
| must | it is necessary (the speaker's view, rules) | Students must wear a uniform. |
| have to / has to | it is necessary (because of outside rules or facts) | She has to work on Saturdays. |
| mustn't | it is not allowed | You mustn't smoke here. |
| don't have to | it is not necessary (but you can) | You don't have to come. It's optional. |
Should: advice
Should gives advice or an opinion about the right thing to do: You should see a doctor. You shouldn't eat so much sugar. What should I do? It is weaker than must: should is advice, must is obligation.
| Present | Past | Future |
|---|---|---|
| can | could / was able to | will be able to |
| must / have to | had to | will have to |
| I can swim. | I could swim when I was six. | I will be able to swim next year. |
| She has to work. | She had to work yesterday. | She will have to work tomorrow. |
Complete the sentence for each situation:
1) Tomorrow is a holiday; there are no lessons. (have to) → We ___ get up early tomorrow.
2) Taking photos in the museum is not allowed. (must) → You ___ take photos here.
3) Aysel has a headache. (should) → She ___ take a rest.
4) Elvin is five, but he reads books. (can) → He ___ read.
5) Yesterday the bus didn't come, so I walked. (have to) → I ___ walk to school.
Show solutionHide solution
2) You mustn't take photos here. — it is forbidden.
3) She should take a rest. — advice.
4) He can read. — ability.
5) I had to walk to school. — obligation in the past: had to.
- 1.I (can) swim when I was five.
- 2.You (must) use your phone during the exam — it's against the rules.
- 3.Tomorrow is Sunday, so we (have to) get up early.
- 4.You (should) eat so many sweets — they are bad for your teeth.
- 5.The bus didn't come, so I (have to) walk to school.
- 6.My sister (have to) wear a uniform at her school.
- 7.My brother is only two, so he (can) read yet.
- 8.Next year I will (can) drive a car.
Key points
- Modal verbs have one form for all persons and no to after them: she can swim.
- Can — ability, permission, requests; could — past ability and polite requests.
- Must and have to express obligation; in the past both become had to.
- Mustn't — it is forbidden; don't have to — it is not necessary.
- Should gives advice: You should see a doctor.
Check yourself
10 questions. Every correct answer earns XP.