Modal Verbs 'can, could, may, might'

In this article we are going to study about the Modal Verbs ‘can, could, may, might’.

We often use ‘can’, ‘could’, ‘may’ and ‘might’ in many similar situations.

‘could’ and ‘might’ are used as the past equivalents of ‘can’ and ‘may’.

We can also use ‘could’ and ‘might’ for present times. In present-time contexts ‘could’ and ‘might’ are used as less positive versions of ‘can’ and ‘may’.

I could buy a Harley. (Less positive and more hesitant than ‘I can buy a Harley.')
Might/Could I borrow your bike? (A diffident way of saying ‘May/Can I …')
It might snow tonight. (Less positive than ‘It may snow …’)

Uses of Can, Could, May, Might

Use Case 1: Ability or Capacity

Concept 1

Using ‘can’ and ‘could’ we denote ability or capacity.

That is, we can use can, can’t (or cannot) (for the present) or could, couldn’t (for the past) when we want to say that someone or something has or doesn’t have the ability or capacity to do something,

He can run pretty complex database queries.

We can’t afford any goof-ups.

Sheldon could solve calculus problems before he was six.

Concept 2: be able to

We can also use ‘be able to’ instead of ‘can/could’ to talk about an ability that someone has or had.

Sachin can / is able to bat well, even though he’s only 14.

He could / was able to run even though he had hamstring injury.

Now, let us see the cases where we prefer one over the other. That is, can/could Vs.

can/could Vs. be able to (With reference to general ability and specific achievement)

In general, we prefer using ‘can/could’ when talking about a general ability.
But we prefer using ‘be able to’ when talking about a specific achievement (particularly if it is difficult, requiring some effort)

could Vs. be able to (With reference to general ability and performance)

Sometimes there’s a subtle difference between having the ability to do something and then actually doing it.

In affirmative past sentences

‘Could’ expresses only ability to do an act, but not the performance of an act.

I could hit long sixes when I was young.

But ‘was/were able to’ expresses both the ability and the action.

When the boat hit the iceberg, we could swim to the bank. (incorrect)
When the boat hit the iceberg, we were able to (or managed to) swim to the bank. (correct)

In negative past sentences

Here we can use either ‘could’ or ‘was/were able to’.

I couldn’t clear the exam. It was beyond my wits. (correct)
I wasn’t able to clear the exam. It was beyond my wits. (correct)

can Vs. be able to (With reference to present and future time)

Concept 1

We don’t use ‘be able to’ when we talk about something that is happening as we are speaking:

You have been working on this engine for long. Do you need some help? – Don’t bother me, I can do it.

Concept 2

To say that something will be possible in the future, we use ‘will be able to’ (rather than ‘can’):

Once this bridge is built, we can drive to work in under an hour. (incorrect)
Once this bridge is built, we will be able to drive to work in under an hour. (correct)

can Vs. be able to (With reference to participle, gerund and infinitive)

Concept 1

We don’t use ‘be able to’ before ‘be + past participle’:

This game can be played by anyone, with just a joystick.

Concept 2

We use ‘be able to’ (rather than can or could), if the idea we want to express needs a to-infinitive, an –ing form, or a perfect tense, or if it follows another modal verb:

We were very lucky to be able to live in India during the 80’s. (to live – to-infinitive)

The fact that I was not being able to talk to you, was the most difficult part.

Since his neck injury last year, he has not been able to perform well.

We may be able to do something about your predicament.

Use Case 2: Permission

Concept 1

To ask permission to do something we use ‘can’ or ‘could’. We can also use them to give/refuse permission.

Can/Could I take another break?

Okay. You can go out.

No, you can’t go out with him.

Concept 2

If we want to put extra pressure on someone to give a positive answer we can use can’t or couldn’t. For example, you might use couldn’t where you expect that the answer is likely to be ‘no’, or where permission has been refused before.

Can’t/Couldn’t we play just a little bit longer? Please?

Concept 3

To give or refuse permission, we prefer can/can’t rather than could/couldn’t.

No, you couldn’t borrow the jacket today. (incorrect)
No, you can’t borrow the jacket today. (correct)

Concept 4: General permission Vs. Permission for one particular action

In Positive Sentences

To report that in the past someone had general permission to do (to do something at any time) → we can use either ‘could’ or ‘was/were allowed to’.

In 1983, women were allowed to vote. (correct)
In 1983, women could vote. (correct)

However, to report permission for one particular past action → we use ‘was/were allowed to’ (not ‘could’)

Although she didn’t have a pass, Jennifer could come in. (incorrect)
Although she didn’t have a pass, Jennifer was allowed to come in. (correct)

In Negative Sentences

In negative sentences, to report that permission was not given, we can use either couldn’t or wasn’t/weren’t allowed to (both in general or in particular situations)

In 1950s, women were not allowed to vote. (correct)
In 1950s, women couldn’t vote. (correct)

We couldn’t / weren’t allowed to attend the school until month-end.

Use Case 3: Offer

Concept 1

When we offer to do something in two ways:

• direct offer or
• offer by making a suggestion

We can use ‘can’ or ‘could’ in both the cases.

Can/Could I help you with your luggage?

You can/could borrow my pen if you want.

Concept 2

We can also use ‘shall’ and ‘should’ to give an offer. We use them in following scenarios:

• In offers that are questions.
  Shall/Should I call a cab for you? (offer given)

• In questions that request confirmation or advice.
  Shall/Should I serve your main course? (confirmation seeked)
  Who shall/should I call? (advice seeked)

Concept 3

We can also use ‘would’ to give an offer. We use it in following scenarios:

• To make an offer, we can use ‘would (you) like’ (but not ‘will…‘)
  Will you like me to get you some coffee? (incorrect)
  Would you like me to get you some coffee? (correct)

• To make a request, we can say ‘I would like’ (but not ‘I will’)
  I will like an apple juice. (incorrect)
  I would like an apple juice. (correct)

Use Case 4: Request

Concept 1

For friendly request, we use ‘can’. While for formal request, we use ‘could’.

Can I take your pen?
Could I talk to the manager, please?

To make a request with authority → We use ‘can’
To make a polite request → We use ‘could’

Could you please keep mum?

Use Case 5: Possibility

Concept 1

Let us first of all consider the Affirmative sentences.

To say there is a possibility of something happening or being true → We generally use ‘may’ or ‘might’ in affirmative sentences.

This may/might be his last major speech before the election.

The news may/might come as a shock to many of the people present.

When Frank gets a job, I may/might get the money back that I lent him.

Concept 2

To express possibility, we can also use ‘could’ (but not ‘can’), instead of may/might.

Aanya is absent today. It may/might/could be because she’s ill.

There may/might/could be some tokens left.

Concept 3

We can also use ‘can’ in some affirmative sentences, especially when we talk about a more general possibility (rather than the possibility of something happening in a particular situation)

The temperature in Sahara desert can sometimes reach 50°C in summer time. (general possibility)

Roses can be white or red. (general possibility)

An idea can change your life. (general possibility)

It can snow tonight. (incorrect; here we are talking about the possibility in a very particular situation)
It may/might/could snow tonight. (correct)

Concept 4: Words commonly used after may, might, could and can

There are some words that we often use with may, might, could and can.

Well

We often use ‘may well, might well or could well’ to say that something is likely in the future.

The revenue of the company may/might/could well reach 50 million this quarter.

We don’t use ‘can well’ in this way to talk about the future. However, ‘can well’ is used to talk about something we think or feel now.

I can well recall how I felt when she left me.

Conceivably and Possibly

The President may conceivably impose an emergency soon. (= it is possible to believe it)

The new environmental laws could possibly lead to cleaner air in our cities.

Concept 5

Now let us consider the Interrogative and Negative sentences.

To say there is a possibility of something happening or being true → We use ‘can’ and ‘could’ in interrogative and negative sentences (just as ‘may’ is used to express possibility in affirmative sentences).

Let us consider Negative sentences first.

In negative sentences (including sentences with words like only, hardly or never), we use ‘can not’ and ‘could not’, to say that something is not possible.

It may rain tomorrow. (affirmative sentence)
It cannot be true. (negative sentence)

There can’t/couldn’t be any bugs left in the code.

There can/could hardly be any doubt that the ball was tampered with.

Concept 6: may not / might not Vs. can not / could not

We use may not or might not to say that it is possible that something is not true, i.e. they denote improbability.

We use can’t or couldn’t to say that it is not possible that something is true, i.e. they denote impossibility.

Compare the use of ‘may/might’ and ‘can/could’ in negative sentences:

There are plans to construct a new metro line, but it may not / might not happen for another few years. (= It is possible that it won’t happen for another few years.)

There are plans to construct a new metro line, but it can’t/couldn’t happen for another few years. (= It is not possible that it will happen for another few years.)

Concept 7

Let us consider Interrogative sentences now.

In interrogative sentences (to ask about the possibility of something happening), we use ‘can’ and ‘could’.

Can this be true? (interrogative sentence)

Could it be that you don’t want to leave?

We can also use phrases like, ‘be likely’.
Is he likely to propose her in near future?

We can even use ‘might’ in these types of questions, but it is considered rather formal:
Might the board of directors be persuaded to change their votes?

Concept 8: may, might, can and could with participle, infinitive and -ing

To talk about a possibility in the past or future, we can use ‘can, could, may and might’ with:

• past participle,
• infinitive and
• -ing

Let’s study them one by one.

Use of may, might, can and could with past participle

To talk about a possibility in the present

She is not there. Where can she have gone? (i.e. Where is it possible that she has gone? – Use of ‘may’ instead of ‘can’ would have expressed annoyance.)

To talk about a possibility in the past

We use ‘could, may and might’ (not ‘can’) with past participle to talk about a possibility in the past.

• To say that it is possible that something happened in the past → We use ‘may/might/could (not ‘can’) + have + past participle’
  
  Where is Anand’s bike? - He may/might/could have taken it with him.
  I thought John is the robber, but I may/might/could have been wrong.

• To say that something was possible in the past, but it did not happen → We use ‘might/could (not ‘may’ or ‘can’) + have + past participle’
  
  The launch might/could easily have gone wrong, but the ISRO scientists resolved a major bug in the system at the eleventh hour.
  If police would not have recovered the missing CCTV footage, then Anand might/could have been the one arrested instead of the real robber.

To talk about a possibility in the future

We use ‘may and might’ with past participle to talk about a possibility in the future.

To say that by some time in the future, it is possible that something will have happened → We use ‘may/might (not ‘can’) + have + past participle’

By next Saturday I may/might have created the required motion graphic.

Use of may, might, can and could with infinitive

We use ‘might’ with infinitive to talk about a possibility in the past.

To talk about what was typically the case in the past → We use ‘might (not ‘may’) + infinitive’

During emergency, the police might arrest you for speaking against the government.

Before 1900s, slaves might be bought and sold in the middle-west in open markets. (passive form)

Use of may, might, can and could with -ing

To say it is possible that something is happening now or to talk about a possible future arrangement → We use ‘may/might (not ‘can’) + be + -ing’

Mak is not here. He may/might be playing at the club. (i.e. possibly he’s playing there right now)

When I become a minister, I may/might be working with Floyd.

Use Case 6: Wish

‘may’ is used to express a wish/blessing/pray (in formal English).

May you succeed! (wish/blessing)
May you live long! (wish/blessing)

‘may’ can also be used for curse.

May enemies of our country die. (curse)

Use Case 7: Reproach

Might is used to express a degree of dissatisfaction or reproach.

You might pay a little more attention to your studies.

Use Case 8

If Principal clause is in present tense, then we often use ‘may’ in subordinate clause.

Such a subordinate clause denotes a purpose and starts with ‘that/so that/in order that’.

We work so that we may earn.

Extra Books and Tools

If you prefer to learn via books, or want some good English Grammar books for reference purposes, you may read this article which enlists some of the books recommended by us.