Grammar › Modal Verbs › May, Might & Could
May, Might & Could
'May', 'might' and 'could' all say something is possible. The differences are small:
- May — possible; also formal permission (It may be true; You may go).
- Might — possible, slightly less certain (She might be at home).
- Could — possible, one option among several (It could be the traffic).
For a negative possibility use 'may not' / 'might not' (He might not know). 'Couldn't' means impossible, not 'possibly not'.
How to use may, might and could
| Meaning | Form | Example |
|---|---|---|
| Present / future possibility | may / might / could + base verb | It might rain later. |
| Negative possibility | may not / might not + base verb | She might not come. |
| Formal permission | may + base verb | You may leave the room. |
| Past guess | may / might / could + have + participle | He may have forgotten. |
All three take the base verb and never change form (it may, she might). May is the most formal.
When to use each
1. Saying something is possible
- It may be true, but I doubt it.
- She might be stuck in traffic.
- That could be the answer.
2. Negative possibility
- They might not know about the change. (perhaps they don’t)
3. Permission (formal)
- You may begin the exam now.
⚠️ Typical error: couldn’t means impossible, not ‘possibly not’: He might not be home (perhaps he isn’t) vs He couldn’t be home — I just saw him at work (it’s impossible).
Common mistakes
1. Adding ‘to’ after the modal. It might to rain → It might rain.
2. Using ‘couldn’t’ for a negative guess. She couldn’t be tired (meaning ‘perhaps she isn’t’) → She might not be tired.
3. Wrong past form. She might forgot → She might have forgotten. Pro tip: may/might/could + base verb = a guess now; may/might/could + have + participle = a guess about the past.
✏️ Practice: May, Might & Could
1. Take a coat — it ___ get cold tonight.
2. I'm not sure where she is — she ___ be at work.
3. Perhaps they don't know yet — they ___ have heard.
4. It's a formal exam. 'You ___ begin now,' said the teacher.
5. Where's Tom? He ___ have missed the train.
6. Don't eat that — it ___ be past its date.
7. That ___ be John at the door — he's abroad this week.
8. Correct this: 'She might forgot the meeting.'
9. The keys ___ be in my bag; let me check.
10. Which sentence is a guess about the PAST?
Frequently asked questions
Is there a real difference between 'may', 'might' and 'could'?
For possibility, they're almost interchangeable. 'May' is a bit more formal; 'might' and 'could' feel slightly less certain. All are followed by the base verb.
How do I make a negative guess?
Use 'may not' or 'might not': She might not be in. Don't use 'couldn't', which means impossible, not 'possibly not'.
Does 'may' also mean permission?
Yes: You may leave now is formal permission. 'Can' is the everyday version: You can leave now.
How do I guess about the past?
Use a modal perfect: She may have left; he might have forgotten; it could have been a mistake.
👩🏫 For teachers
CEFR objectives for “May, Might & Could”:
- Can use 'may', 'might' and 'could' for present and future possibility (CEFR B1).
- Can form negative possibility with 'may not' / 'might not' and distinguish it from 'couldn't' (impossible).
- Can recognise 'may' for formal permission.
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