Modal Verbs

Modal verbs are a small closed class of helper verbs that sit before a main verb and express possibility, ability, obligation, permission, prediction, advice, and willingness. The principal modals are:

can, could, may, might, must, shall, should, will, would, ought to

Plus a few semi-modals: need to, have to, used to, dare, had better.

Modals are everywhere in English. Mastering them is one of the most important steps in moving from A1 to B2 fluency.

How modals work — the grammatical rules

Modals don’t behave like normal verbs. They have several quirks:

1. No -s in the third person

✅ He can swim. (not he cans) ✅ She should leave. (not she shoulds)

2. No to before the next verb

✅ I must go. (not I must to go) ✅ You can stay. (not you can to stay)

Exception: ought to and have to keep the to.

3. No do/does/did in questions and negations

✅ Can he swim? (not Does he can swim?) ✅ I cannot leave. (not I don’t can leave)

The modal itself inverts for questions and takes not for negation.

4. No infinitive, gerund, or participle

You can’t say to can, canning, or canned (as a modal). When you need these forms, English uses substitute expressions:

I want to be able to swim. (be able to = substitute for “can”) I have to leave. (have to = substitute for “must” in past/future)

5. Modals are followed by the bare infinitive (no to)

can swim, should leave, must wait

6. Past forms are idiosyncratic

Could is the past of can, would is the past of will, should of shall, might of may. But these past forms also have present meanings (politeness, hypothetical). They are NOT just past forms.

Each modal in turn

Can / Could

Can expresses:

• Ability: I can swim.
• Permission: Can I open the window?
• Possibility: It can be cold here in winter.
• Offer: Can I help you?

Could is the past of can (for ability), but also has present meanings:

• Past ability: When I was young, I could run fast.
• Polite request: Could you help me? (softer than can you)
• Hypothetical possibility: That could be true. (less certain than can)
• Past possibility: He could have been a great musician.

May / Might

May expresses:

• Permission (formal): You may sit down.
• Possibility: It may rain.

Might is technically the past of may, but in modern English it’s used for:

• Slightly less certain possibility: It might rain. (slightly less likely than may)
• Past possibility: She might have left already.

In practice, may and might are nearly interchangeable for possibility. Might is slightly more tentative.

Must

Must expresses:

• Strong obligation (internal): I must finish this today.
• Logical deduction: He must be tired after all that work.
• Strong recommendation: You must read this book!

Must not = prohibition: You must not enter.

For past obligation, English uses had to (not musted). For absence of past obligation, didn’t have to.

Have to (semi-modal)

Have to is similar to must but expresses external obligation.

I have to go to work. (external — it’s required) I must finish this. (internal — I’ve decided)

The distinction is subtle and often blurred. Have to is the more common form in modern English.

Have to conjugates fully (have to, has to, had to, will have to). Must doesn’t.

Shall / Should

Shall is now mostly literary or used in offers:

• Offer/suggestion: Shall we go? Shall I close the door?
• Formal future (1st person): We shall meet again. (archaic)
• Legal/contractual obligation: The buyer shall pay the seller…

Should is far more common, expressing:

• Recommendation/advice: You should rest.
• Mild obligation: Students should arrive on time.
• Expectation: The package should arrive tomorrow.
• Past regret (with have + past participle): I should have told you.

Will / Would

Will expresses:

• Future: I will be there. (see future-tenses)
• Willingness/promise: I will help you.
• Habitual present: He will sometimes spend hours reading. (gives a flavor of typical behavior)

Would is the past of will but also has present meanings:

• Polite request: Would you help me?
• Conditional/hypothetical: I would buy a house if I had the money.
• Past habit: When I was a child, I would visit my grandmother every Sunday.
• Past future (reported speech): He said he would come.

Ought to (semi-modal)

Ought to means should — moral or expected obligation:

You ought to apologise. He ought to know better.

In modern English, should is more common; ought to is slightly formal.

Need to (semi-modal)

Need to expresses requirement:

I need to go.

In British English, need can also be used as a modal (You needn’t worry), but this is somewhat formal. In American English, need to is the standard form.

Used to

Used to expresses past habits or past states that are no longer true:

I used to smoke. (not anymore) She used to live in Berlin.

This is a fossilised modal — it never has a present form, never works as uses to.

Modal + perfect (past unreality)

A powerful use of modals is modal + have + past participle, which expresses past possibility, regret, or unreality.

Examples:

You could have helped me. (you didn’t, but you had the option) I should have called. (I regret not calling) She must have left already. (logical deduction) He can’t have known. (impossibility — he didn’t know)

This construction is one of the most expressive features of English modals.

What you don’t need to do

You don’t need to conjugate modals like regular verbs. They have no -s, no -ing, no -ed. They sit in this grammatical category alone.

You don’t need to use to after them. Must go, not must to go. Exception: ought to.

You don’t need to use do/does/did in modal questions. Can you?, Should I?

You don’t need to memorise every nuance at A1. Start with can, must, should, then expand to would, might, could, may at A2/B1.

Common confusions

• Modals never take -s. He can, not he cans. She should, not she shoulds.
• No to before the verb. I must go, not I must to go. Exception: ought to and have to.
• Past forms aren’t just past. Could, would, should, might all have important present-time uses (politeness, hypothesis, recommendation).
• Modal + perfect for past unreality. I should have called = I didn’t call but wish I had. This construction expresses regret, missed opportunity, or past deduction.

Where you’ll meet it in the library

Modals are in every page of English literature. Especially visible in:

• Pride and Prejudice (A2+) — Austen’s dialogues are full of modal verbs because her characters argue, deduce, propose, and refuse. The Darcy proposal scene is a masterclass.
• A Christmas Carol (A2+) — Dickens uses modals for the moral weight of Scrooge’s transformation. Must, will, should have carry the philosophical content.
• The Picture of Dorian Gray (B1+) — Wilde’s epigrams use modals constantly to express possibility, obligation, and permission in social commentary.