Modal Verbs – Present Modal
Deduction & Speculation – Must, may, might, could, can 3

Modal Verbs for Possibility & Deduction (Present)

🔍Modal Verbs for Possibility & Deduction (Present)

📝We use modal verbs to guess, speculate, or deduce about the present. They show how sure (or not sure) we are.

1️⃣Degrees of Certainty

✅MUST = we are sure something is true (strong deduction)
❌CAN'T / CANNOT = we are sure something is not true (strong deduction)
🤔MAY / MIGHT / COULD = something is possible (but we are not sure)
🌐CAN = shows general possibility (in general, not deduction about now)

2️⃣Structures

👉Formula: Subject + modal + be / verb

a) (strong certainty, positive deduction)

✅Affirmative: She must be tired. She worked all night.
❌Negative: She can't be tired. She slept 10 hours.
❓Interrogative: Can she be tired after sleeping so much?

b) (50% - maybe yes, maybe no)

✅Affirmative: He may/might/could be at the library.
❌Negative: He may not/might not be at school today. ⚠️ We don't use could not for present deduction
❓Interrogative: Could he be at the library?

c) (general possibility, not deduction)

✅Affirmative: Life can be difficult sometimes.
❌Negative: Life can't be easy all the time.
❓Interrogative: Can life be that simple?

3️⃣Comparison Table

Modal	Meaning (certainty)	Affirmative	Negative	Interrogative
must	Strong deduction (sure it's true)	She must be a teacher.	She can't be a student.	Can she be a teacher?
may / might / could	Possibility (50/50)	He might be at school.	He might not be home.	Could he be at school?
can	General possibility	It can be dangerous to swim here.	It can't be safe without a helmet.	Can it be dangerous?

4️⃣Common Mistakes ❌✅

❌She must to be tired.
✅She must be tired.
❌He could not be at school. (for deduction)
✅He might not be at school.
❌Can't he tired?
✅Can't he be tired?

✨Quick Tips

💯Use must when you are almost sure (95–100%).
🚫Use can't when you are sure something is impossible.
🤷Use may / might / could when you are not sure (50%).
🌐Use can for general truths, not for specific deductions.

📝More Examples

✅MUST Examples (95-100% certain):

😴He must be sleeping. His room is dark and quiet.
🏠They must be home. The lights are on.
💰This car must be expensive. It's a Ferrari!

🤔MAY/MIGHT/COULD Examples (50% possibility):

📚She might be studying in the library.
🌧️It could be raining outside.
🚗He may be driving to work right now.

❌CAN'T Examples (impossible):

👴He can't be 20 years old. He looks much older.
🏖️She can't be at the beach. It's snowing!
💤They can't be sleeping. The music is too loud.

🌐CAN Examples (general possibility):

☀️Weather can be unpredictable in spring.
🎯Learning English can be challenging but rewarding.
🍕Pizza can be both healthy and delicious.

💭Remember

💯MUST = 95-100% certain (strong positive deduction)
🚫CAN'T = 0% certain (strong negative deduction)
🤷MAY/MIGHT/COULD = 50% certain (possibility)
🌐CAN = general possibility (not specific deduction)
⚠️Don't use could not for present deduction
📝Always use be after modal verbs for states