Modals in English Grammar

Modals in English grammar are used with a main verb to add further meaning to the sentence. They show things such as possibility, ability, regret, or necessity.

In this lesson we'll explain the form of modal verbs and then their function with examples.

Form of Modal Verbs

The Basic Rules

Modal verbs are auxiliary verbs (helper verbs) formed by placing them in front of the main verb in a clause. They will not tend to appear on their own, unless it's clear from the context what it means.

These are the main rules. They:

have no 's' for the 3rd person: "He can go" NOT "He cans go"
are followed by the bare infinitive i.e. no 'to': "He can go" NOT "He can goes"
are made negative by adding not/n't: I can't/cannot; mustn't/must not
are inverted with the subject to make a question: Can you go?

This is the basic structure:

Structure of Modal Verbs:

Affirmative: Subject + Modal Verb + Bare Infinitive
He can go
Negative: Subject + Modal Verb + Not + Bare Infinitive
He cannot go
Interrogative: Modal Verb + Subject + Bare Infinitive
Can he go?

Here are some examples of modal verbs in use with main verbs.

Examples of Modals:

She might not go
He can't swim
We must get there soon
We ought to revise harder
John should take his test again
They shouldn't feel upset
I have to help her
Q: Will you help her? A: Yes, I have to. (no main verb following the modal as it's clear from the question).

Semi- or Marginal Modal Verbs

You'll have noticed from the examples that some of the modal verbs had 'to'. There are several modals in English grammar that have some exceptions to some of the rules above, and they are called semi-modal or marginal modal verbs.

They have some of the grammatical characteristics of 'pure' modal verbs. One of the basic differences is that most are followed by the infinitive (i.e. with 'to') rather than the bare infinitive.

Marginal Modal Verbs with 'to':

She ought to have helped us
They have (got) to arrive early
We need to work harder
He is able to speak Latin
They used to go to the school in our village

Another marginal modal in English grammar is had better, which is different because it is made up of two words.

We had better check the train timetable

These marginal modals can differ in the way they are made negative or interrogative. We'll look in more details at these in another lesson that will be coming soon.

Learn more about semi-modal verbs.

Modals in the Past

Most modal verbs can also be used in the past. When we do this, we add have + past participle after the modal verb.

Examples of Modals in the Past:

She might not have gone
He can't have swum
They must have got there sooner
We ought to have revised harder
John should have taken his test again
They shouldn't have felt upset

Function of Modals in English Grammar

Modals in English grammar are used with a main verb to change its meaning. Take a look at this example:

I do my homework every night
I must do my homework every night

The first one is just a factual statement. The person does their homework each night. However, the second one by using 'must' is showing that the person has no choice in this - it's an obligation, for whatever reason.

There are a variety of modals in English grammar and each one differs in how they change the meaning of a sentence. Some can have more than one use. We'll now look in more details at when we use them.

Possibility

Could
May
Might

These are used to indicate the possibility, probability, or impossibility of something happening or being true.

Examples of Possibility:

They could get here by train as we have a train station down the road
He may decide to come tomorrow instead
I might not bother going to my class

Learn more about modals of possibility >>

Ability

Can
Could
Be able to

The modal can is used to show what someone is able to do, whereas can't or cannot show what someone is unable to do. For the past, could is used.

Being a marginal modal verb, be able to is a modal in meaning but not form. It has the verb to be so can be used in different tenses.

Examples of Ability:

She can speak French very well
He can't drive
She could walk by the time she was 1 and half years old
He's not able to come to the phone at the moment
They weren't able to pass the test

Learn more about modals of ability >>

Asking Permission

May
Can
Could

The modal can is also used to ask for permission. Could is also used as a polite form of this, as is may.

Examples of Asking Permission:

Can/May I help you?
Could I join you for dinner tonight?

Learn more about modals of permission >>

Requests

Will
Would
Can
Could

Can is slightly less polite than the others.

Examples of Requests:

Will you please turn your music down?
Could you help me with this essay?
Can you close the window?
Would you mind arriving a bit early?

Learn more about modal verbs of request >>

Suggestions/Advice

Should
Ought to
Had better

Should and had better are by far the more common than ought to. Should tends to be used over Ought to or had better to make questions.

Examples of Suggestions/Advice:

You should have taken the medication.
We ought to go and see our parents
Shouldn't you be worried about how you'll get there?
We'd (had) better check we locked all the windows

Obligation/Necessity

Must
Have to
Need to

Though need to has been placed here, it could feasibly be placed as a modal of suggestion/advice as it's not quite as strong as must or have to.

Examples of Obligation/Necessity:

We must buy a new car as our current one is so old now
You mustn't change your mind again
They have to get a visa before coming here
Do you have to look at me like that?
You needn't come if you don't want to

Habits

Will
Would
Used to

Will is used for habits in the present or future, while would and used to are used for past habits - used to specifically for habits that have stopped.

Examples of Habits:

I will always be the person who stops to help others
She would often arrive late when she worked here
He used to like Thai food but now he hates it

Regrets

Should have
Would have
Could have

Regrets are things from the past that we wish we'd done differently now, so the past form of the modal is always used: modal + have ('ve) + past participle.