Modals auxiliaries are a special class of verbs that indicate degrees of probability and necessity. Many ESL learners have trouble with modal auxiliaries. Below is a chart giving examples. Verbs in italics are not used very often.
| MODALS | USES | PRESENT/FUTURE | PAST |
|---|---|---|---|
| May | Polite request | May I borrow your pen? | |
| Formal permission | You may leave the room. | ||
| Possibility | Where’s John? He may be at the library. I’m not sure. | Where was John? He might have been at the library. | |
| Might | Possibility | Where’s John? He might be at the library. I’m not sure. | Where was John? He might have been at the library. |
| Polite request | Might I borrow your pen? | ||
| Should, had better | Advisability | I should study tonight. I had better study tonight. |
I should have studied last night. |
| 90% certain | She studied very hard. She should do well on the exam tomorrow. | She studied very hard. She should have done well on the exam yesterday. | |
| Ought to | She ought to do well on the exam tomorrow. | She ought to have done well on the exam yesterday. | |
| Could | Past ability | I could run fast when I was a child. | |
| Polite request | Could I borrow your pen? | ||
| Suggestion | I need help in math. You could talk to your teacher. | You could have talked to your teacher. | |
| Less than 50% possibility | Where is John? He could be at home. | Where was John? He could have been at home. | |
| Impossibility | That couldn’t be true! | That couldn’t have been true! | |
| Would | Polite request | Would you please pass the salt? | |
| Preference | Would you mind if I left early? | ||
| I would rather go to the park than stay home. | I would rather have gone to the park. | ||
| Repeated action in the past | When I was a child, I would visit my grandparents every weekend. |