Modal Verbs: Can, Could, Should, Would, Must, and More

Modal verbs are small words with a lot of work to do. They help you say whether something is possible, required, allowed, likely, advisable, or within someone’s ability. Put one before a main verb, and the meaning changes immediately: “go,” “can go,” “should go,” and “must go” do not say the same thing.

English has nine central modal verbs: can, could, may, might, shall, should, will, would, and must. Because they appear constantly in speech and writing, learning how each one works will make your English clearer, more natural, and more exact.

Modal Verbs in Plain English

Modal verbs are auxiliary, or helping, verbs. They join with a main verb to express modality: ideas such as ability, permission, necessity, possibility, willingness, and expectation. They belong to the English verb system, but they do not follow the same patterns as ordinary verbs.

How Modal Verbs Behave

Modal verbs have several grammar rules of their own:

• Use "not" to make negatives: "He cannot drive at night" (not "He does not can drive at night").
• Use inversion for questions: "Could you wait here?" (not "Do you could wait here?").
• No infinitive form: English does not use "to can" or "to must."
• No "-s" with he, she, or it: "My brother can cook" (not "my brother cans cook").
• No past participle: Forms such as "has musted" and "have canned" are not used as modal forms.
• Use the bare infinitive after a modal: "They should leave" (not "they should to leave").

Using Can and Could

How to Use Can

1. Present ability:

• "Maya can play the violin beautifully."
• "I can ride a bike, but I can't fix one."

2. Informal permission:

• "You can borrow my charger."
• "Can I sit next to you?"

3. General possibility:

• "Desert nights can get surprisingly cold."
• "Starting a new job can feel overwhelming."

4. Requests:

• "Can you send me the file before lunch?"

How to Use Could

1. Ability in the past:

• "Before his injury, Daniel could lift heavier weights."

2. Polite requests, usually softer than "can":

• "Could you open the window, please?"

3. Possibility, with less certainty than "can":

• "The meeting could end early." (That is possible, but not certain.)

4. Suggestions:

• "We could ask the manager for advice."

5. Conditional sentence patterns:

• "If I saved enough money, I could visit Japan next year."

Using May and Might

How to Use May

1. Formal permission:

• "May I ask a question?"
• "Guests may enter through the side door."

2. Moderate possibility:

• "The store may close early tonight." (A 50/50 chance.)
• "Nina may still be in the office."

How to Use Might

1. Possibility, often weaker than "may":

• "The store might close early tonight." (Less likely than "may.")
• "Omar might join us for dinner."

2. Hypothetical situations:

• "If we booked today, we might get a better price."

3. Polite suggestions:

• "You might want to save a copy first."

Using Shall and Should

How to Use Shall

"Shall" appears most often in British English, formal writing, and legal language:

• Future meaning, formal and first person: "We shall meet again." (This is less usual in modern American English, where "will" is more common.)
• Formal or legal obligation: "The contractor shall complete the work by June 30."
• Offers and suggestions with first person: "Shall I carry that bag?" "Shall we begin?"

How to Use Should

1. Advice and recommendations:

• "You should back up your photos."
• "He should practice before the audition."

2. Expectation:

• "The bus should arrive in ten minutes." (I expect it to.)
• "Laura should know the answer by now."

3. Obligation, but softer than "must":

• "Employees should report safety problems immediately."

4. Formal conditional use:

• "Should you require more information, contact our office." (= If you should require...)

Using Will and Would

How to Use Will

• Spontaneous decisions: "I 'll take the blue one, thanks."
• Requests: "Will you hold this for a moment?"
• Future: "They will move into the new apartment next week."
• Habits or tendencies: "The cat will scratch the sofa when she is bored." (characteristically)
• Promises: "I will call as soon as I land."

How to Use Would

• Preferences: "I would rather eat outside."
• Future in the past: "She said she would explain later."
• Polite requests: "Would you please lower the volume?"
• Past habits: "Every summer, my grandparents would take us to the lake."
• Hypothetical or conditional meaning: "If I had a larger kitchen, I would bake more often."

How Must Works

1. Strong obligation or necessity:

• "Visitors must wear ID badges." (It is required or essential.)
• "I must submit the application tonight."

2. Logical deduction, showing certainty:

• "They must be home — the lights are on." (I feel very sure this is true.)
• "You must be hungry after that long flight."

3. Prohibition in the negative:

• "You must not park in front of the emergency exit." (It is forbidden.)

Be careful with this contrast: "must not" means prohibition, or "do not do it." "Do not have to" means there is no obligation; you are not required to do it, though you may if you choose.

Verb Phrases That Act Like Modals

Some verb phrases work much like modals, although their grammar is not identical:

• had better: Strong advice or a warning — "You had better save your work now." (Consequences are implied.)
• be able to: Ability — "Marco will be able to attend." (Useful where "can" cannot be conjugated.)
• need to: Necessity — "We need to leave soon."
• have to: Obligation, often from an outside rule or situation — "I have to renew my license this week." (Close to "must," but with an external requirement.)
• be going to: Future intention — "I am going to clean the garage on Saturday."
• ought to: Advice or moral obligation — "You ought to tell the truth." (Similar to "should.")

Quick Comparison Chart

Mistakes to Watch For

• "Can" for formal permission: In highly formal situations, "may" is usually preferred to "can" when asking or granting permission.
• "Must not" vs. "don't have to": "You mustn't enter" means entry is forbidden. "You don't have to enter" means entry is optional.
• Double modals: "She might could help" is nonstandard, although it is found in some Southern US dialects. In Standard English, say "She might be able to help."
• "Must" + "to": "He must to leave" is incorrect. Say "He must leave."

Modal verbs let you fine-tune what you mean. With one short word, you can turn a statement into a request, a rule, a guess, a warning, a promise, or a piece of advice. Once you understand can, could, may, might, shall, should, will, would, and must — plus common semi-modals — you can express degrees of certainty, duty, permission, and possibility much more accurately.