Modal verbs

The rule in one minute

Modal verbs are helping verbs: can, could, may, might, must, shall, should, will, would. They come before a main verb and change its meaning:

• ability: She can swim.
• permission: You may leave.
• possibility: It might rain.
• obligation: You must stay.
• likelihood: They should arrive soon.

Two firm rules keep modals correct.

1. After a modal, use the base verb. Do not add to, -s or -ing. Write She can swim, not She can to swim or She can swims.
2. For the past, use have plus a past participle: She must have left. He should have known.

The second rule explains a famous mistake. Spoken could’ve sounds like could of. But of can never follow a modal. The word is always have.

Where the marks are

Modals matter in two ways. For accuracy, could of is a common and very visible error, and a wrong verb form after a modal is a correctness fault.

For expression, modals let you set how strong a claim is. In analysis, this suggests is careful, but this proves may go too far. In argument, the government should act is milder than the government must act.

Controlling certainty like this is a sign of mature writing.

Wrong and right

• Wrong: I could of finished it on time. Right: I could have finished it on time.
• Wrong: She must to apologise for the delay. Right: She must apologise for the delay.
• Wrong: He can plays three instruments. Right: He can play three instruments.
• Wrong: They should have went earlier. Right: They should have gone earlier. Use the past participle after have.
• Too strong: This detail proves the writer hates the city. Better: This detail suggests the writer dislikes the city. A softer modal fits the evidence.

Try it yourself

Correct each sentence, then check below.

1. You should of told me sooner.
2. The evidence must to be examined again.
3. She might comes to the meeting later.
4. If we had left earlier, we could caught the train.

Answers: (1) You should have told me sooner. (2) The evidence must be examined again. There is no to. (3) She might come to the meeting later. Use the base verb. (4) If we had left earlier, we could have caught the train. A past modal takes have and a past participle.

Make it a habit

Run two checks. First, after every modal, make sure the next word is a plain base verb. Second, if you are writing about the past, write have, never of.

A quick edit pass helps: search your writing for of after could, should, would, might and must.

Then think about strength. When you make a claim, ask how sure you really are. Use may, might or could for careful points, should for advice, and must or will for strong claims you can prove.

Where students get stuck, and how we help

Many students know the rule but write could of when typing or writing fast. They also use proves where the evidence only suggests. In our English as a Second Language lessons, a teacher corrects these in your own work and coaches you to match the modal to the strength of your evidence.

Lessons start from RM70/hr. You can book a paid one-hour trial to try it.

Next step

Practise the forms in the practice area. Then read about conditionals and reported speech. Use the proofreading guide on your last essay.

Next, visit our original practice tasks to use the rule in your own writing. Our IGCSE English tuition page explains how lessons run. When you are ready, the paid one-hour trial is the first step.