Have you ever wondered how to express possibility, ask for permission, or talk about what could happen in the future? These kinds of ideas often rely on modal auxiliaries.

These are little words that help us talk about what is possible, necessary, or allowed. In this blog, we’ll explore how these words work and why they’re so important in everyday English.

What are Modal Auxiliaries?

Modal auxiliaries are special helping words that pair up with main verbs to create what we call potential verb-phrases. These phrases help us express different shades of meaning—like when something might happen, or when someone can do something.

Several helping verbs are used to create verb phrases that show ability, possibility, obligation, or necessity. These kinds of verb phrases are called potential phrases, meaning  phrases of possibility.

 Example:

♦ She can swim. (ability)
♦ You must do your homework. (necessity)
♦ They might go to the park. (possibility)

The helping verbs used in potential phrases include: may, can, must, might, could, would, and should. These are called modal auxiliaries, and the base form of the verb always follows them without ‘to.’ 

 Examples:

♦ May: We may ask him a few questions.
♦ Can: I can drive a car.
♦ Must: You must ask for directions.
♦ Might: He might give you a chance.
♦ Could: I could show you his house if you would let me.
♦ Should:’I should enjoy a sea voyage.

These words don’t stand alone; they always need another verb to go with them. For example, in ‘she can swim,’ ‘can‘ is the modal, and ‘swim‘ is the main verb.

Note: The verbs like ‘give‘ in phrases such as ‘can give‘ are in their base form (infinitive). You can see this by comparing ‘I can strike‘ with ‘I am able to strike,’ ‘I may strike‘ with ‘I am allowed to strike,’ and ‘I must strike‘ with ‘I am required to strike.’ In the past, when verbs had special endings (like -an or -en), it was easier to tell that these were infinitives.

Related Reading: Exploring Adverbs: Types, Examples, and Uses 

Forming Potential Verb-Phrases with Modals

Forming sentences with modal auxiliaries is pretty straightforward. The basic structure looks like this:

Modal + Base Form of the Verb

Here’s how it works:

♥ Positive Sentence: She can dance.
♥ Negative Sentence: She can’t dance.
♥ Question: Can she dance?

In each case, the base form of the verb (follows the modal (like ‘can’) like ‘dance’). Notice that in negative sentences, we usually add ‘not’ right after the modal, and in questions, we switch the order of the modal and the subject.

Potential Mood

Potential phrases can be organized into tables like verb conjugations. When grouped together, these phrases are often called the potential mood. Here’s how they look in different tenses:

Active Voice

Present Tense

Past Tense

Perfect or Present Perfect Tense

Past Perfect

Passive Voice

Using Modal Auxiliaries

Let’s look at ways that we can use modal auxiliaries.

Can and Could

Can (past tense: could) is used to show that someone can do something. It shows ability.

♦ Example: Sanjay can ride a bicycle.
♦ Example: Jose could swim.

May and Might

May (past tense: might) is used in different ways: Permission, Possibility, and Wishes.

Permission

♦ Example: You may borrow my pencil.
♦ Example: I told him that he might join our party.

Possibility or Doubt

♦ Example: He may accept my offer.
♦ Example: You might not like it.

Wishes

♦ Example: May good fortune be with you!

Note: When asking for permission, it’s correct to say ‘May I?’ instead of ‘Can I?’ But for negatives, ‘can‘ is more common. 

♥ Question: May I play ball this morning?
♥ Answer: No, you can’t; but you may play this afternoon.

Must

Must is used to express something that is necessary or an obligation.

Examples:

♦ We must all die someday.
♦ You must wait for the train.
♦ You must not be discouraged by failure.

Note: Although ‘must‘ originally was a past tense, it’s now almost always used in the present. To talk about past necessity, we use ‘had to,’ like in ‘I had to wait for the train.’

Should and Ought

Should with the present form of a verb shows what you should do now, duty and moral obligation, while with the past form, it shows what you should have done before. Ought can be used in the same way.

Note: ‘Ought’ comes from an old past tense of the word ‘owe.’ In modern English, it’s rarely used but always in the present. You should not add ‘had’ before ‘ought.’

People can also express what is expected in certain situations using ‘should’.

♦ Example: Three weeks should/ought to be enough time.
♦ Example:If the train is on time, he should/ought to arrive at six.

Would

Would is sometimes used to show a regular action or habit in the past.

♦ Example: I would gaze at the sea for hours at a time.
♦ Example: Whenever we asked Aram about his adventures, he would start talking about something else.

Related Reading: Understanding Verbs: The Action Words of Language

Nuances in Meaning

Modal auxiliaries aren’t all the same; each one brings a different level of certainty or meaning to the sentence

‘She might come to the party‘ suggests it’s possible but uncertain. If you say, ‘She will come to the party,’ you’re much more sure. ‘You may go outside‘ gives permission, while ‘You must stay inside‘ shows a rule or obligation. Modals can make requests sound more polite. ‘Could you help me?’ sounds nicer than ‘Can you help me?’

‘Can‘ talks about ability, while ‘may‘ is for permission. So, ‘Can I go to the bathroom?‘ asks if you’re able to, but ‘May I go to the bathroom?‘ asks if you’re allowed to.

‘Should‘ is for suggestions or advice, like ‘You should study.’ ‘Must‘ is much stronger, like a rule: ‘You must study.’

Knowing these differences helps you pick the right word for what you want to say.

Practice Exercises

Choose the correct modal auxiliary for each sentence.

1. You (should / must) finish your homework before watching TV.
2. (Can / May) I borrow your book for the weekend?
3. She (could / should) play the piano when she was five years old.
4. We (might / must) attend the meeting tomorrow, but we’re not sure yet.
5. You (can / should) ask for help if you don’t understand the lesson.
6. They (could / would) go to the park every Saturday when they were kids.
7. I (may / can) have a slice of cake if there’s any left.
8. He (must / could) submit his assignment by Friday, no exceptions.
9. You (might / would) like this movie; it’s really interesting.
10. She (should / can) call her friend to apologize.
11. We (would / might) leave early if the weather is bad.
12. (Can / Would) you please pass the salt?
13. They (must / may) be very tired after their long journey.
14. You (can / could) be right, but I’m not entirely sure.
15. She (should / must) drink more water to stay hydrated.
16. He (could / must) have forgotten about the meeting.
17. You (may / must) pay the bill before leaving the restaurant.
18. They (can / should) take a break if they’re feeling tired.
19. I (could / should) see the mountains from my window when I was younger.
20. (May / Would) I have a glass of water, please?

Key Takeaways

1. Express Ability with ‘Can’ and ‘Could’: Use ‘can’ to talk about present abilities and ‘could’ for past abilities.
2. Use ‘May’ and ‘Might’ for Possibility: ‘May’ and ‘might’ both express possibility, but ‘might’ often suggests a lower probability. E
3. Ask for Permission with ‘May’: ‘May’ is the polite and correct way to ask for permission.
4. Use ‘Must’ for Strong Necessity: ‘Must’ expresses something that is essential or required.
5. Use ‘Should’ for Advice: Use ‘should’ to give advice or recommendations.

6. Use ‘Would’ for Hypotheticals: ‘Would’ is often used to describe hypothetical situations or to make polite requests.
7. Express Past Possibilities with ‘Might Have’: Use ‘might have’ to talk about something that could have happened but didn’t.
8. Use ‘Would’ for Repeated Past Actions: ‘Would’ can describe habitual actions in the past.
9. Use ‘Will’ for Future Certainty: ‘Will’ is used to express something you are sure will happen in the future.
10. Combine Modals with ‘Have’ for Past Events: Combine a modal with ‘have’ and the past participle to talk about past events.

Last Words on Modal Auxiliaries

Modal auxiliaries might seem small, but they have a big job in helping us express possibilities, make requests, and talk about what’s necessary or allowed.

So next time you’re speaking or writing, think about which modal best fits what you want to say, and don’t be afraid to mix things up!

Happy writing!

Linda