Modals of Ability: Can, Could, Be able to, May, Might
Introduction
These five verbs are examples of modal verbs.
- can
- could
- be able to
- may
- might
Modal verbs are helping/auxiliary verbs that express ideas like ability, permission, possibility, and necessity. Many modal verbs have more than one meaning. They are always followed by the simple form of a verb. For example,
Alan can swim well.
This shows that Alan has the ability to swim.
1. Modals for Ability
Let’s start with expressing ability! We use can, be able to and could to show that someone has (or doesn’t have) an ability to do something.
Look at these examples:
| Present/Future Ability | Negative | Past Ability | Negative |
|---|---|---|---|
| Alan can swim well. | Jackie cannot play piano. | Paul could speak Chinese when he was a child. | Mary couldn’t finish her homework last night. |
| I can meet you after school. | We can’t visit Vancouver this weekend. | Last night, there were no clouds in the sky and they could see all the stars. | You couldn’t find the website this morning, could you? |
| I am able to speak two languages. | I am not able to speak Arabic. | When I was a young child, I wasn’t able to tie my shoes. | I wasn’t able to finish my test yesterday. |
| Brenda is able to run quickly. | Stacey isn’t able to finish a marathon. | Shaun was able to complete the assignment. | Paula wasn’t able to pass the class. |
| You are able to program a computer. | We aren’t able to make a reservation tonight. | They were able to catch six fish on their trip. | You weren’t able to understand the answer, were you? |
Did you notice that the verbs after “can/could/be able to” are always in the simple form? For example:
Alan can swim well. (subject + auxiliary verb + simple verb + …)
Do NOT change the modal auxiliary OR the main verb for he/she/it subjects. In addition, do not add “ing” or “ed”.
Alan can swims well. 
Wrong!
Alan can to swim well. Wrong!
Alan can swimming well. Wrong!
Alan could swam well. Wrong!
How can we make questions about ability? It’s easy!
Modal auxiliary + subject + main verb + … ?
Can she play guitar?
Could you speak English when you were a child?
BE + subject + able to + main verb + … ?
Are you able to understand the homework?
Were you able to finish the test?
Was he able to pass the exam?
Notice that we do not need the verbs “do/does/did” when we make questions!
The modal verb “be able to” includes the word “to”; the “to” is not an infinitive.
2. Modals for Possibility
Let’s learn about expressing possibility now.
The verbs may, might and could show possibility now and in the future. In this case, they have the same meaning.
Look at this conversation:
A: My mother said that it may snow tomorrow.
B: Really? It might snow?! That’s great! I could make a snowman or go for a “snow” walk.
A: Don’t get too excited. If the temperature is high, it may not snow. It may rain.
B: Well, I guess I could still go for a walk in the rain.
Be careful with may + “be” and “maybe”. Compare these sentences. Both are correct.
Ann is not here today. She may be sick. “may be” is a modal.
Ann is not here today. Maybe she is sick. “Maybe” is an adverb.
3. Modals for Permission
Finally, let’s look at ways to ask for and give permission. We use may, could and can to do this.
| Formality | Example |
|---|---|
| most formal/polite | May I go to the washroom? *only used with “I” and “we” |
| medium formal | Could I borrow your dictionary? Could he pay you tomorrow? |
| casual | Can I call you back later? Can she have a cookie? |
Now, look at the (main) verbs that come after the subject. They are always in the simple form, just as with other modal verbs.
Again, the most polite/formal way to answer these questions is with “may.”
Examples:
| May I go to the washroom? | Yes, you may (go to the washroom). Yes, you can. | No, you may not. No, you cannot. |
| Can she have a cookie? | Yes, she can. | No, she can’t. |
Notice that we do not “contract” may + not = mayn’t. Wrong!
4. Modal verbs obligation :
must, have to, should and ought to , need to
There are two types of modal verbs of obligation ;
- those that primarily express a firm obligation or necessity – must and have to
- those that express a recommendation or moral obligation – should and ought to , and need to
Firm obligation, etc. – must and have to
The verb must only exists in the simple present and present perfect forms.
While the present form can express obligation, necessity, certainty or strong probability, the present perfect forms only express a strongly felt opinion or supposition.
| All persons | Present | Present perfect |
| Affirmative | must | must have |
| Negative | must not, mustn’t | must not have, mustn’t have |
If other tenses are required, the speaker or writer must use forms of the synonymous modal verb “have to” . This modal auxiliary has all normal tenses, including progressive or continuous forms; these are not common, but need to be used in some cases.
| Principal tenses | Present | Present perfect | Past | Future |
| Affirmative: | has to, have to | has had to have had to | had to | will have to |
| Negative; | does not have to, do not have to , doesn’t have to don’t have to | has not had to have not had to | did not have to didn’t have to * | will not have to won’t have to |
| Progressive or continuous | am having to is having to, are having to | has been having to have been having to | was having to were having to | will be having to |
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Got to :
In spoken English, and in the present form only, have to is often substantiated by the word got;
For example an alternative to I have to is I’ve got to.
For more on this, see Get and got
Examples of must and have to being used to express :
a. Firm obligation or necessity
b. Certainty or strong probability.
c. Must have only : supposition
a1) You must see a doctor at once !
a2) I have to be at school tomorrow at 8 a.m. I have an exam !
a21) I’ve got to be at school tomorrow at …..
a3) You mustn’t touch that plate, it’s too hot.
a4) I had to see a doctor, because I felt very sick.
a5) I had to break the window ! I lost my key !
a6) The manager isn’t here, he’s had to go to Washington on urgent business.
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b1) He must be over eighty, he was born in 1930.
b2) If my brother’s not in London, he has to be in New York.
c1) I can’t find my laptop, I must have left it in the train.
c2) If they’re out, they mustn’t have heard the news.
Take care !
Take care to distinguish correctly between “had to” and “must have“
They had to go to London
= They were obliged to go to London
They must have gone to Chicago
= In my opinion, they have certainly gone to Chicago.
► Other uses of the verb have: see the verb to have.
Must and have to in negative contexts
It is vital to remember that must not and don’t have to are NOT synonyms – indeed they mean two completely different things.
Must not implies negative obligation (i.e. being forbidden to do something)
Don’t have to implies the absence of obligation (i.e. having no obligation to do something)
Compare:
They must not go to London
= They must stay away from London, they cannot go there.
They do not have to go to Chicago
= They are not obliged to go to Chicago, but they can go there if they wish.
Recommendation or moral obligation – should and ought to, need to
a) should, ought to
The verb should only exists in the simple present, and present perfect forms
Forms of should
| All persons | Present | Present perfect |
| Affirmative | should | should have |
| Negative | should not, shouldn’t | should not have, shouldn’t have |
The verb ought to only exists in simple present and present perfect forms
Forms of ought to
| All persons | Present | Present perfect |
| Affirmative | ought to | ought to have |
| Negative | ought not to, oughtn’t to | ought not to have, oughtn’t to have |
Should and ought to are more or less synonymous
Examples:
a1) You should stop smoking ( = You ought to stop smoking.)
a2) It’s raining hard, the children ought to come indoors.
a3) I didn’t know you were married ! You ought to have told me !
a4) If you’d wanted to succeed, you should have worked harder at school.
a5) This pullover’s got holes in it, I should get a new one.
a6) This pullover’s got holes in it, I ought to get a new one.
a7) That’s awful ! You really oughtn’t to have done that, you know !
b) Need to :
Used affirmatively, need to implies strong recommendation; but used negatively it expresses an absence of obligation. There are two negative forms of need, either don’t need to or needn’t.
Take care! Needn’t is never followed by to. Need is also used as a main verb followed directly by an object, as in I need you.Examples:
b1) I’ve been working non-stop for six hours, I need to take a rest.
b2) I think you’ve got covid….. you need to get tested at once.
b3) Thank goodness, I haven’t got covid, so I don’t need to stay at home
b4) Thank goodness, I haven’t got covid, so I needn’t stay at home.
