Common mistakes to avoid when using modal verbs in English

Modal verbs are an essential part of English grammar. They can be used to express possibility, ability, permission or obligation, among many other things. Unlike other verbs, modal verbs in English have unique characteristics, which often create common errors when using them. Understanding and using modal verbs in English correctly can significantly enhance your fluency and accuracy in English. 

Modal Verb	Use	Example sentence/s
Can	Ability, permission, possibility	I can swim.  Can I leave early today?  It can get very cold in Aberdeen.
Could	Ability, polite requests, possibility	I could read when I was three. Could you help me, please? It could rain later.
May	Possibility, permission	We may go to the beach tomorrow.  May I use your phone?
Might	Possibility	We might go out for dinner tonight.
Must	Obligation, necessity, strong belief	You must wear a seatbelt.  This must be the right address.
Shall	Suggest or ask for advice	Shall we go out for lunch?
Should	Give advice, express expectation, obligation	You should go to the dentist if you have a toothache.  He should arrive by midday.
Will	Future intention willingness or certainty	I will call you later.  I will help you with that.
Would	Polite requests, hypothetical situations, express a habit in the past	Would you pass the salt, please?  I would travel more if I had more money.  When I was young, I would play outside for hours.
Ought to	Similar to ‘should’	You ought to drive more slowly when the roads are wet.
Had better	Give advice or recommend a preferred course of action. It implies a negative consequence if the advice isn’t followed	You had better finish your homework before you go out.

Common grammar mistakes when using modal verbs in English 

1. Incorrect tense formation

Many people mistakenly change the tense of modal verbs or add auxiliary verbs like will or going to for future forms. Remember, modal verbs do not change form for tense.

Incorrect: He will can go.

Correct: He will be able to go.

2. Adding ‘s’ for third person singular

Unlike regular verbs, modal verbs in English do not require an ‘s’ for the third person singular form.

Incorrect: She cans swim.

Correct: She can swim.

3. Misuse of ‘to’ after modal verbs

A common grammar mistake is adding to directly after a modal verb. The correct structure is: 

modal verb + base form of the verb.

Incorrect: I must to leave.

Correct: I must leave.

4. Formation of negatives

Some people often incorrectly form negatives by using do not with a modal verb. Instead, add not directly after the modal verb.

Incorrect: I don’t can swim.

Correct: I cannot swim.

5. Incorrect use of modals for ability

Avoid using another modal verb before you use can. If you want to do this, use be able to instead, especially in different tenses.

Incorrect: She might can attend.

Correct: She might be able to attend.

6. Negatives and opposites

It’s important to understand what the negative forms or opposites of modal verbs are. It’s also important to understand that the negatives of modal verbs like have to and must do not always mean the exact opposite of the affirmative word. For example: 

• have to is a personal requirement to yourself, whereas don’t have to means there is no obligation
• must means that something is an obligation, while mustn’t implies that something is prohibited

7. Past modals with of instead of have

Another common grammar mistake is using of instead of have with modals in the past form.

Incorrect: He must of gone.

Correct: He must have gone.

8. Can’t vs mustn’t

It’s important to understand the difference between can’t (impossibility) and mustn’t (prohibition). These are often confused. 

Can’t implies something is not possible. e.g. You can’t stand in front of that yellow line. 

Mustn’t implies something is forbidden. e.g. You mustn’t bring a calculator into the exam room. 

 

By avoiding these common mistakes, you can enhance your communication skills and express yourself more clearly and accurately. Keep practising, and you’ll find yourself using modal verbs in English naturally and authentically in no time.

 

Activity

1. You ought	A. better finish your report for the teacher or there may be consequences.
2. You had	B. helmet when you are cycling on the road.
3. If you want, I will	C. for a walk in the park?
4. Shall we go	D. to apologise for being late.
5. You must wear a	E. rain tomorrow.
6. There’s a chance it might	F. sing very well.
7. My sister can	G. help you move house next month.
8. You should visit	H. the room when you hear the bell.
9. If I had the time and money, I would	I. the doctor if you’ve had this stomach ache for more than a couple of days.
10. You may enter	J. visit every country in Europe.

Answers

1. D
2. A
3. G
4. C
5. B
6. E
7. F
8. I
9. J
10. H

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Billie Jago is an ELT writer and teacher trainer specialising in digital learning materials and assessment resources. She has written for various well-known assessment titles, and writes items for high stakes exams such as the PTE, IELTS and Cambridge. Alongside materials writing, she delivers international teacher training sessions and is the founder of the ELTcpd professional development training platform and podcast. She is also the co-founder of the educational consultancy, OtterEducation.