Modal Verbs

Remember that modal verbs are a type of auxiliary verbs, which are a type of verb. See the diagram below.

While the auxiliary verbs to be and to have are pretty simple – they are just used to create aspect – modal verbs are very complicated. They are used for a large number of different purposes.

This lesson will explain everything about modal verbs.

Four Notes on Modal Verbs

There are four pieces of information that you should know when it comes to modal verbs:

1) Besides what they are used for, a big thing that makes modal verbs different from the auxiliary verbs to be, to have, and to do is that modal verbs can never be the main verb in a sentence.

For example, with the auxiliary verb to have you can say:

I had had a good day until I got hurt.

Where the first had is an auxiliary verb and the second had is the main verb.

This will never happen with modal verbs, because they can never be the main verb in a sentence.

2) Some modal verbs have a ‘past tense version’ that they match with in certain situation, such as with reported speech. For example:

Jack said, “I can do it.”

Jack said that he could do it.

Anna said, “I may lose my job.”

Anna said that she might lose her job.

Jane said, “I shall go the park.” [Shall is old and rarely used]

Jane said that she should go to the park.

John said, “I will go to the park.”

John said that he would go to the park.

However, these ‘past tense versions’ are only used in certain situations, and you should not think of them like this. There is only one modal verb that has a true past tense, and that is can, whose past tense is could, and that’s only for specific uses of can.

For other modal verbs, you have to create a past tense version with a perfect infinitive.

Perfect Infinitive: modal verb + have  + past participle

NOTE: Some meanings of the modal verbs cannot be made past tense with the perfect infinitive. You will see how this works for every modal verb below.

3) Whenever a ‘present’ modal verb is used, the main verb will always be in the bare infinitive form. For example:

Italics = Modal Verb | Underline = Main Verb

John isn’t here. He may be at the library.

I can eat fifty eggs.

The main verb will never change to any other form. For example:

John isn’t here. He may is at the library.

John isn’t here. He may was at the library.

John isn’t here. He may been at the library.

John isn’t here. He may being at the library.

I can ate fifty eggs.

I can eaten fifty eggs.

I can eating fifty eggs.

Whenever a perfect infinitive modal is used, the main verb will always be in the past participle form. For example:

John wasn’t there. He may have been at the library.

The main verb will never change to any other form. For example:

John wasn’t there. He may have be at the library.

John wasn’t there. He may have was at the library.

John wasn’t there. He may have being at the library.

4) No double modals. You cannot use two modal verbs in the same compound verb. For example:

I might can jump over this table.

The Modal Verbs and Their Uses

There are 15 modal verbs, but 3 of them are almost never used.

Can

Could

May

Might

Must

Have to

Shall

Should

Will

Would

Ought to

Had better

Used to

Dare

Need

Let’s go through and talk about each of the ten modal verbs that used.

NOTE: the modal verbs each work completely differently from each other. There is no pattern in their use or meaning.

Can

Negative: cannot / can’t

Uses:

Ability

Possibility (Non-specific situation)

Giving Permission

Requests

Impossibility (Can’t)

Ability: Used to show that you are able to do something.

Past Version: could

I can speak English means "I am able to speak English" or "I know how to speak English."

Possibility: Used to show that something has a chance of happening or being true. Can isn’t used to talk about specific events.

Past Version: could

People can be upset after a breakup means “It’s possible for people to feel upset after going through a breakup.”

Giving Permission: Used to show that you are allowed to do something.

Past Version: could

You can smoke here means "you are allowed to smoke here."

In formal English, may is usually preferred. But using can is extremely common.

Requests: Used to ask someone to do something for you.

Past Version: ✘

Can you hand me that pencil?

Using could is a bit more polite. (Could you hand me that pencil?)

Impossibility: Used to say that you believe something is not possible or is not true.

Past Version: can’t have (rare) / couldn’t have

People can’t be unhappy after winning $1 million means “It’s not possible for people to be unhappy after winning $1 million.”

That can’t be John. He’s in Australia means “It’s not possible for that person to be John because he’s in Australia.”

Could

Negative: could not / couldn’t

Uses:

Past tense of can (only for ability, giving permission, possibility)

Possibility (Specific situation)

Requests

Possibility: Used to show that something has a chance of happening or being true. Could is used to talk about specific events.

Past Version: could have

It could be raining in Siem Reap right now means “It is possible that it’s raining in Siem Reap right now.”

Requests: Used to ask someone to do something for you.

Past Version: ✘

Could you hand me that pencil?

Using can is a bit less polite (Can you hand me that pencil?).

May

Negative: may not

Uses:

Possibility (Specific situation)

Giving Permission

Requesting Permission

Irrelevance

Express a Hope

Possibility: Used to show that something has a chance of happening or being true. May is used to talk about specific events.

Past Version: may have

It may be raining in Siem Reap right now means “It is possible that it’s raining in Siem Reap right now.”

Note: Could/May/Might each are used to show that something is possible. They mean the same thing.

Giving Permission: Used to show that you are allowed to do something.

Past Version: ✘

You may smoke here means "you are allowed to smoke here."

In formal English, may is usually preferred. But using can is extremely common.

Requesting Permission: Used to ask someone for permission to do something.

Past Version: ✘

May I use that pencil? means “Do I have your permission to use that pencil?”

This is slightly different than a request with can or could, which usually suggests an action, but can also be used to request permission. May is more limited because it cannot be used to suggest an action. It can only be used to request permission. For example, while with can/could you are able to say:

Could you open that window?

You can’t do this with may. That is, you can’t suggest that someone else do an action.

May you open the window?

Because of this, may is far more formal than can/could.

Irrelevance: Used to show a lack of importance in response to a truth.

Past Version: may have

He may be taller than me, but he still can’t beat me in basketball means “Although I agree that he is taller than me, it doesn’t matter, because I am still able to beat him in basketball.”

Express a Hope: Used to say something you hope to happen.

Past Version: ✘

May you live long and happy means “I hope that you live a happy, long life.”

May God save us means “I hope that God saves us.”

Might

Negative: might not

Uses:

Possibility (Specific situation)

Giving Permission

Requesting Permission

Irrelevance

Possibility: Used to show that something has a chance of happening or being true. Might is used to talk about specific events.

Past Version: might have

It might be raining in Siem Reap right now means “It is possible that it’s raining in Siem Reap right now.”

Note: Could/May/Might each are used to show that something is possible. They mean the same thing.

Giving Permission: Used to show that you are allowed to do something.

Past Version: ✘

You might leave now means "you are allowed to leave now.”

May is far more commonly used for giving permission. Using might is very polite and soft.

Requesting Permission: Used to ask someone for permission to do something.

Past Version: ✘

Might I use that pencil? means “Do I have your permission to use that pencil?”

Just as with may, might is more limited because it cannot be used to suggest an action. It can only be used to request permission. It is even more polite than using may.

Irrelevance: Used to show a lack of importance in response to a truth.

Past Version: might have

He might be taller than me, but he still can’t beat me in basketball means “Although I agree that he is taller than me, it doesn’t matter, because I am still able to beat him in basketball.”

There is no difference in meaning between may and might here.

Should

Negative: should not / shouldn’t

Uses:

Giving Advice

Obligation

Expectation

Giving Advice: Used to give a recommendation.

Past Version: should have

You should try Khmer food means “I think it’s a good idea for you to try Khmer food.”

Obligation: Used to describe how it is expected that you behave because of what is normal in your community or because the behavior is right/wrong.

Past Version: should have

You should drive on the right side of the road means “It is expected by everyone here that you drive on the right side on the road, so you also need to do it.”

You should not lie means “It is not acceptable to lie.”

Expectation: Used to show that you expect something to happen.

Past Version: should have

You should receive my letter in two days means “I expect that the letter I sent you will arrive in two days.”

This should work means “Because of all the information I know, I believe and expect that this will work.”

Will

Negative: will not / won’t

Uses:

Futurity

What Generally Happens

Capacity

Giving Commands

Willingness

Habitual Aspect

Futurity: Used to create the future tense in English.

Past Version: would

I will be at the park means “I expect to be at the park at some time in the future.”

What Generally Happens: Used to say what always happens in a particular situation or what is generally true.

Past Version: ✘

A dropped ball will fall towards the ground means “Generally, anytime a ball is dropped, it falls towards the ground.”

This is used to talk about general situations, not any specific ones. So, it does not make sense to use a past version of it. General facts are true, no matter when they happen.

Capacity: Used to talk about something being able to do something because it has enough of something.

Past Version: ✘

The classroom will easily fit 25 students means “The classroom is big enough for 25 students to easily fit inside of it.”

Giving Commands: Used to give a command; in other words, to tell someone to do something.

Past Version: ✘

You will be quiet! means “I am demanding that you be quiet.”

Willingness: Used to show that someone is willing to do something; in other words they would agree to do it if you asked them.

Past Version: would

The baby won’t eat anything means “The baby is able to eat something but is choosing not to.”

Habitual Aspect: Used to create the habitual aspect, which describes how a person habitually behaves. In other words, it is used to describe someone when they’re behavior is very predictable.

Past Version: would / used to

Jack will get mad at anything means “Jack has a habit of getting mad about almost everything.”

The past version of this (would / used to) is more commonly used than the present.

Would

Negative: would not / wouldn’t

Uses:

Unreal Situation

Request

Uncertain Opinion

Expected Behavior (Disapproving)

Unreal Situations: Used to talk about any situation that is not actually real; in other words, imagined situations.

Past Version: would have

It would be lovely to see you means “I am not seeing you now and I don’t have plans to see you, but if I did see you, I would like it.”

Requests: Used to politely ask someone to do something for you.

Past Version: ✘

Would you hand me that pencil?

This is a polite way of requesting something. It’s about equal to using could, meaning it’s more polite than using can.

Uncertain Opinion: Used to give an opinion on something when you’re not very sure about it. Used with words: think/imagine/hope/say.

Past Version: would have

I would imagine that they’re home by now.

I would hope John is smart enough to know not to do that.

I would think that anyone with an IELTS score of 9.0 could spell “cat.”

This can also be used to make giving your opinion more polite, since when you make your statement less certain, it is sounds softer to the listener. For example:

How much do you think I weigh?

I would say about 80 kilos.

Expected Behavior (Disapproving): Used to show that some behavior is typical of a person. This is used in a negative way that shows dislike of the person being spoken of. It is also informal. 

Past Version: would have

You would go and spoil it, wouldn’t you!

She insists that she did nothing wrong, but then she would say that, wouldn’t she?

Must

Negative: don’t have to / doesn’t have to

Uses:

Obligation

Certainty

NOTE: Must does not have a negative. You cannot attach a not to must, like you can with can, will, etc. However, must can be followed by not, it will just be applied to the following word, not to must. For example:

You must not kill.

In this example, we are saying that you must do some thing, and that thing is not killing.

Another way of saying that we must do something is that we have to do something. So, if we want to create a negative for this modal verb, we can do that by using the negative of have to.

You don’t have to go.

He doesn’t have to do the assignment.

Obligation: Used to describe how it is expected that you behave because of what is normal in your community or because the behavior is right/wrong.

Past Version: ✘

You must drive on the right side of the road means “It is expected by everyone here that you drive on the right side on the road, so you also need to do it. In other words, you are required to drive on the right side of the road.”

You must not lie means “It is not acceptable to lie. In other words, you are required not to lie.”

Certainty: Used to express certainty, particularly when the conclusion is reached through logic (deduction).

Past Version: must have

The answer isn’t A, B, or C, so it must be D means “Because we know that the answer is not A, B, or C, we are certain that it is D.”

Have to / Has to

Negative: don’t have to / doesn’t have to

Uses:

Obligation

Certainty

Obligation: Used to describe how it is expected that you behave because of what is normal in your community or because the behavior is right/wrong.

Past Version: had to

You have to drive on the right side of the road means “It is expected by everyone here that you drive on the right side on the road, so you also need to do it. In other words, you are required to drive on the right side of the road.”

You have to not lie means “It is not acceptable to lie. In other words, you are required not to lie.”

Certainty: Used to express certainty, particularly when the conclusion is reached through logic (deduction).

Past Version: had to

The answer isn’t A, B, or C, so it has to be D means “Because we know that the answer is not A, B, or C, we are certain that it is D.”

Ought to

Negative: ought not (to)

Uses:

Giving Advice

Obligation

Expectation

Ought to is less commonly used than should and has the exact same uses as it. However, you still see it used today. Notice that the negative of it is ought not to, or more commonly: ought not.

Giving Advice: Used to give a recommendation.

Past Version: ought to have

You ought to try Khmer food means “I think it’s a good idea for you to try Khmer food.”

Obligation: Used to describe how it is expected that you behave because of what is normal in your community or because the behavior is right/wrong.

Past Version: ought to have

You ought to drive on the right side of the road means “It is expected by everyone here that you drive on the right side on the road, so you also need to do it.”

You ought to not lie means “It is not acceptable to lie.”

Expectation: Used to show that you expect something to happen.

Past Version: ought to have

You ought to receive my letter in two days means “I expect that the letter I sent you will arrive in two days.”

This ought to work means “Because of all the information I know, I believe and expect that this will work.”

Had better

Negative: had better not

Uses:

Giving Advice

Obligation

Had better has the same uses as should or ought to, except it is never used for expectation.

Giving Advice: Used to give a recommendation.

Past Version: ✘

You had better try Khmer food means “I think it’s a good idea for you to try Khmer food.”

Obligation: Used to describe how it is expected that you behave because of what is normal in your community or because the behavior is right/wrong.

Past Version: ✘

You had better drive on the right side of the road means “It is expected by everyone here that you drive on the right side on the road, so you also need to do it.”

You had better not lie means “It is not acceptable to lie.”

Had better is commonly used when the situation is immediate, such as:

I had better get to work.

It is also commonly used in threats:

You had better give me all your money right now, or else!

Used to

Negative: didn’t use to

Uses:

Habitual Aspect (Past)

Used to is only used to create the habitual aspect in the past tense. It cannot be used to talk about present habits – will is used for that.

Would can be used to mean the same thing, but it can’t be used with linking verbs, whereas used to can. See more.