1. Lesson Overview
In this lesson, you will learn:
- Form of may, might, and must
- Permission (formal usage)
- Possibility and probability
- Logical deduction (present)
- Degrees of certainty
- Must vs have to (preview)
- Common errors
These modals express how certain we are about something.
2. Form Structure
A. Affirmative
Subject + may/might/must + base verb
She may attend the conference.
It might rain tonight.
Scientists must analyze the data carefully.
B. Negative
may not
might not
must not (mustn’t)
She may not come.
It might not be true.
You must not cheat.
C. Questions
May/Might/Must + subject + base verb?
May I leave early?
Must we submit the report today?
Note: “Might” is rarely used in questions.
3. Use of May
A. Formal Permission
May I enter the room?
More formal than “can.”
B. Possibility (Medium Probability)
She may arrive late.
The results may change.
4. Use of Might
A. Weak Possibility (Less Certain)
It might rain tomorrow.
She might attend the lecture.
Might is slightly less certain than may.
5. Use of Must
A. Obligation
Students must submit assignments on time.
Strong obligation.
B. Logical Deduction (High Certainty)
She must be tired. (I am almost sure.)
The lights are off. They must be asleep.
High confidence based on evidence.
6. Degrees of Certainty
Strong certainty → must
Medium possibility → may
Weak possibility → might
Example:
She must be at home. (very certain)
She may be at home. (possible)
She might be at home. (less certain)
7. Must Not vs Don’t Have To
Must not → prohibition
Don’t have to → no obligation
You must not smoke here. (prohibited)
You don’t have to come tomorrow. (optional)
This distinction is critical.
8. Common Mistake Spotlight
⚠ Adding “to” after modal
Incorrect: She may to come.
Correct: She may come.
⚠ Confusing must and have to
Must = speaker’s authority
Have to = external rule
⚠ Using double modal
Incorrect: She might can come.
Correct: She might come.
9. End of Lesson Check
You should now be able to:
- Use may for formal permission
- Use might for a weak possibility
- Use must for obligation and deduction
- Express degrees of certainty
- Avoid structural mistakes