Using Modal Verbs for Advice, Obligation, and Permission: English Grammar Guide

Modal verbs are auxiliary verbs that express the speaker’s attitude toward an action or situation. They help convey meanings such as advice, obligation, permission, ability, or possibility. In this guide, we focus on how modal verbs function when giving advice, expressing obligation or duty, and asking or giving permission. Mastering these uses is essential for natural and polite English communication.

Understanding Modal Verbs

Modal verbs are followed by the base form of a main verb (without “to”). For example:

• You should study harder.

• You must wear a seatbelt.

• You may enter now.

Common modal verbs include: can, could, may, might, shall, should, will, would, must, and ought to.

Each modal verb carries a specific meaning and level of formality. When used properly, they add nuance and precision to your communication.

1. Modal Verbs for Giving Advice

When you want to give advice, make recommendations, or express what you think is the best action, English uses should, ought to, and had better.

a. Using “should”

“Should” is the most common modal verb for giving advice. It’s neutral and polite.

• You should see a doctor.

• You should eat more vegetables.

• Students should review their notes every day.

You can also use shouldn’t to express negative advice:

• You shouldn’t smoke inside the building.

• You shouldn’t stay up too late.

Tip: “Should” suggests a good idea, not a rule. It’s softer than “must.”

b. Using “ought to”

“Ought to” has a similar meaning to “should,” but it’s slightly more formal and less common in everyday conversation.

• You ought to apologize to her.

• He ought to be more careful next time.

In negative form, “ought not to” is used, but it sounds old-fashioned:

• You ought not to drive so fast.

c. Using “had better”

“Had better” is stronger than “should.” It implies a warning or a negative consequence if the advice is ignored.

• You had better finish your homework before going out.

• We had better leave now, or we’ll miss the bus.

Negative form:

• You had better not tell anyone about this.

Note: “Had better” sounds urgent and is used when something bad might happen if the advice isn’t followed.

2. Modal Verbs for Expressing Obligation and Necessity

To talk about rules, duties, responsibilities, or something that is required, we use must, have to, and should (for softer obligation).

a. Using “must”

“Must” expresses a strong obligation or something that is required by rules or laws. It often reflects the speaker’s authority or personal judgment.

• You must wear a seatbelt.

• Employees must arrive on time.

• I must remember to call my mother.

Negative form:

• You must not (mustn’t) park here. → It’s prohibited.

Important: “Mustn’t” means not allowed, not not necessary.

b. Using “have to”

“Have to” also shows obligation, but it’s more objective—it expresses external rules or requirements, not the speaker’s opinion.

• I have to go to work at 8 a.m. (Because my company requires it.)

• You have to show your ID to enter the building.

Negative form:

• You don’t have to come early. (It’s not necessary, but you can if you want.)

Compare:

• You mustn’t smoke here. = It’s not allowed.

• You don’t have to smoke. = It’s optional.

c. Using “should” for softer obligation

When you want to sound polite or less strict, “should” can replace “must.”

• You should wear a mask in crowded places.

• People should respect traffic rules.

This makes your sentence more advisory than commanding.

3. Modal Verbs for Asking and Giving Permission

To ask or grant permission, English uses can, could, and may. The level of politeness changes depending on the verb.

a. Using “can”

“Can” is informal and commonly used in daily conversation.

• Can I borrow your pen?

• Can we sit here?

To give permission:

• You can use my laptop.

• Students can leave early today.

Negative form:

• You can’t go out now.

b. Using “could”

“Could” is more polite and formal than “can.” It’s often used in requests or when speaking to someone you don’t know well.

• Could I open the window?

• Could we join your group?

To give permission politely:

• You could take a short break if you’re tired.

However, “could” is often used to ask for permission rather than give it.

c. Using “may”

“May” is the most formal modal verb for permission. It is often used in professional or academic contexts.

• May I come in?

• May we leave early today?

To grant permission:

• You may start your exam now.

• Guests may enter through the main gate.

Negative form:

• You may not enter this area. (Formal prohibition)

Note: “May” sounds polite but can feel too formal in casual settings.

4. Comparing Levels of Politeness

Example:

• Can I go out? → (friendly, casual)

• Could I go out? → (polite, respectful)

• May I go out? → (formal, old-fashioned in casual speech)

5. Common Mistakes with Modal Verbs

1. Using “to” after a modal verb

   • ❌ You should to study.

   • ✅ You should study.

2. Mixing up “mustn’t” and “don’t have to”

   • ❌ You mustn’t come tomorrow. (means forbidden)

   • ✅ You don’t have to come tomorrow. (means optional)

3. Using wrong modal for tone

   • ❌ May I borrow your phone? (too formal for friends)

   • ✅ Can I borrow your phone? (natural in daily speech)

4. Using double modals

   • ❌ You must can go.

   • ✅ You must be able to go.

6. Practical Dialogues

Example 1 – Advice

• A: I have a headache.

• B: You should take a rest.

Example 2 – Obligation

• A: Do I have to wear a uniform?

• B: Yes, students must wear one every day.

Example 3 – Permission

• A: Can I leave early today?

• B: Yes, you may go now.

7. Summary Table

8. Tips for Learners

• Use should for general advice.

• Use must or have to for rules or laws.

• Use can in friendly situations, may in formal ones.

• Avoid overusing must, as it can sound too strong or demanding.

• Remember: modal verbs never change form—no “-s,” “-ing,” or “-ed.”

9. Practice Sentences

Try completing these sentences:

1. You ______ see a dentist if your tooth hurts.

2. Employees ______ arrive before 9:00 a.m.

3. ______ I borrow your umbrella?

4. You ______ not smoke here.

5. You ______ study harder if you want to pass.

Answers: should, must, may/can, mustn’t, had better.

Conclusion

Modal verbs like should, must, and may are key tools for expressing advice, obligation, and permission. The choice of modal verb depends on how strong, polite, or formal you want your message to be. By mastering their differences and practicing in real-life contexts, you can speak English more naturally, respectfully, and effectively.

Modal verbs might seem small, but they carry big meaning — they shape how your message is received, whether it sounds friendly, strict, or polite. Use them thoughtfully, and your English will sound both accurate and confident.