Chapter 11: Modal Verbs — Ability, Permission, Obligation, and Possibility

Modal verbs are auxiliary verbs that express mood — the speaker’s attitude toward an action. They are followed by the base form of the main verb (no to, no -s).

Complete Modal Verb Reference Table

Modal	Main Meanings	Present/Future Example	Past Example
can	ability, informal permission	She can speak French.	She could speak French as a child.
could	past ability, polite request, possibility	Could you help me?	I couldn’t find it.
may	formal permission, possibility	You may leave now.	(might have)
might	weaker possibility, suggestion	It might rain later.	She might have forgotten.
must	strong obligation (internal), deduction	You must stop at red lights.	He must have been tired.
have to	external obligation, necessity	I have to submit it by Friday.	She had to leave early.
should	advice, recommendation, expectation	You should see a doctor.	You should have called.
will	future, willingness, prediction	I will help you.	(would)
would	polite request, hypothetical, habit	Would you mind closing the door?	He would walk to school every day.
shall	formal future (I/we), offer/suggestion	Shall we begin?	—

Modals for Deduction

Modals can express how certain you are about something:

Certainty	Present	Past
100% sure (positive)	He must be home.	He must have been home.
~80% sure	She should be there by now.	She should have arrived.
~50% possible	It may/might be true.	It may/might have been true.
100% sure (negative)	That can’t be right.	That can’t have been right.

Common Mistakes

1. Double modal: ❌ You might can do it. → ✅ You might be able to do it.
2. Must vs. have to in negatives: You mustn’t do it (prohibition) ≠ You don’t have to do it (not obligatory)
3. Could vs. was able to for single past achievement: ❌ I could finish it in time. → ✅ I was able to finish it in time.

Modals for Politeness Levels

Informal → Formal	Request
Most informal	Can you help me?
More polite	Could you help me?
Formal	Would you help me?
Very formal	Would you mind helping me?

Key Checklist

• I can use modal verbs correctly with the base form of the main verb.
• I understand the difference between must (prohibition) and don’t have to (no obligation) in negatives.
• I can use modals for deduction (must/might/can’t + have + past participle).