MODAL VERBS ( MODAL AUXILIARIES )

Modal auxiliary verbs may sound difficult but in fact they're easy. They are invariable (no conjugation). And the main verb is always the "bare infinitive" (the infinitive without "to").

Can, Could, Be able to

Can and could are modal auxiliary verbs. Be able to is NOT an auxiliary verb (it uses the verb be as a main verb). We include be able to here for convenience.

Can

Can is an auxiliary verb, a modal auxiliary verb. We use can to:

• talk about possibility and ability
• make requests
• ask for or give permission

Structure of Can

subject + can + main verb

The main verb is always the bare infinitive (infinitive without "to").

	subject	auxiliary verb	main verb
+	I	can	play	tennis.
-	He	cannot	play	tennis.
		can't
?	Can	you	play	tennis?

Notice that:

• Can is invariable. There is only one form of can.
• The main verb is always the bare infinitive.

Use of Can

can: Possibility and Ability

We use can to talk about what is possible, what we are able or free to do:

• She can drive a car.
• John can speak Spanish.
• I cannot hear you. (I can't hear you.)
• Can you hear me?

Normally, we use can for the present. But it is possible to use can when we make present decisions about future ability.

1. Can you help me with my homework? (present)
2. Sorry. I'm busy today. But I can help you tomorrow. (future)

can: Requests and Orders

We often use can in a question to ask somebody to do something. This is not a real question - we do not really want to know if the person is able to do something, we want them to do it! The use of can in this way is informal (mainly between friends and family):

• Can you make a cup of coffee, please.
• Can you put the TV on.
• Can you come here a minute.
• Can you be quiet!

can: Permission

We sometimes use can to ask or give permission for something:

1. Can I smoke in this room?
2. You can't smoke here, but you can smoke in the garden.

(Note that we also use could, may, might for permission. The use of can for permission is informal.)

Could

Could is an auxiliary verb, a modal auxiliary verb. We use could to:

• talk about past possibility or ability
• make requests

Structure of Could

subject + could + main verb

The main verb is always the bare infinitive (infinitive without "to").

	subject	auxiliary verb	main verb
+	My grandmother	could	swim.
-	She	could not	walk.
		couldn't
?	Could	your grandmother	swim?

Notice that:

• Could is invariable. There is only one form of could.
• The main verb is always the bare infinitive.

Use of Could

could: Past Possibility or Ability

We use could to talk about what was possible in the past, what we were able or free to do:

• I could swim when I was 5 years old.
• My grandmother could speak seven languages.
• When we arrived home, we could not open the door. (...couldn't open the door.)
• Could you understand what he was saying?

We use could (positive) and couldn't (negative) for general ability in the past. But when we talk about one special occasion in the past, we use be able to (positive) and couldn't (negative). Look at these examples:

	Past
	General	Specific Occasion
+	My grandmother could speak Spanish.	A man fell into the river yesterday. The police were able to save him.
-	My grandmother couldn't speak Spanish.	A man fell into the river yesterday. The police couldn't save him.

could: Requests

We often use could in a question to ask somebody to do something. The use of could in this way is fairly polite (formal):

• Could you tell me where the bank is, please?
• Could you send me a catalogue, please?

Be able to

Although we look at be able to here, it is not a modal verb. It is simply the verb be plus an adjective (able) followed by the infinitive. We look at be able to here because we sometimes use it instead of can and could.

We use be able to:

• to talk about ability

Structure of Be able to

The structure of be able to is:

subject + be + able + infinitive

	subject	be main verb	able adjective	infinitive
+	I	am	able	to drive.
-	She	is not	able	to drive.
		isn't
?	Are	you	able	to drive?

Notice that be able to is possible in all tenses, for example:

• I was able to drive...
• I will be able to drive...
• I have been able to drive...

Notice too that be able to has an infinitive form:

• I would like to be able to speak Chinese.

Use of Be able to

be able to: ability

We use be able to to express ability. "Able" is an adjective meaning: having the power, skill or means to do something. If we say "I am able to swim", it is like saying "I can swim". We sometimes use "be able to" instead of "can" or "could" for ability. "Be able to" is possible in all tenses - but "can" is possible only in the present and "could" is possible only in the past for ability. In addition, "can" and "could" have no infinitive form. So we use "be able to" when we want to use other tenses or the infinitive. Look at these examples:

• I have been able to swim since I was five. (present perfect)
• You will be able to speak perfect English very soon. (future simple)
• I would like to be able to fly an airplane. (infinitive)

Have to, Must, Must not/Mustn't

Must is a modal auxiliary verb.

Have to is NOT an auxiliary verb (it uses the verb have as a main verb). We include have to here for convenience.

Have to (objective obligation)

We often use have to to say that something is obligatory, for example:

• Children have to go to school.

Structure of Have to

Have to is often grouped with modal auxiliary verbs for convenience, but in fact it is not a modal verb. It is not even an auxiliary verb. In the have to structure, "have" is a main verb. The structure is:

subject + auxiliary verb + have + infinitive (with to)

Look at these examples in the simple tense:

	subject	auxiliary verb	main verb have	infinitive (with to)
+	She		has	to work.
-	I	do not	have	to see	the doctor.
?	Did	you	have	to go	to school?

Use of Have to

In general, have to expresses impersonal obligation. The subject of have to is obliged or forced to act by a separate, external power (for example, the Law or school rules). Have to is objective. Look at these examples:

• In France, you have to drive on the right.
• In England, most schoolchildren have to wear a uniform.
• John has to wear a tie at work.

In each of the above cases, the obligation is not the subject's opinion or idea. The obligation is imposed from outside.

We can use have to in all tenses, and also with modal auxiliaries. We conjugate it just like any other main verb. Here are some examples:

	subject	auxiliary verb	main verb have	infinitive
past simple	I		had	to work	yesterday.
present simple	I		have	to work	today.
future simple	I	will	have	to work	tomorrow.
present continuous	She	is	having	to wait.
present perfect	We	have	had	to change	the time.
modal (may)	They	may	have	to do	it again.

Must (subjective obligation)

We often use must to say that something is essential or necessary, for example:

• I must go.

Structure of Must

Must is a modal auxiliary verb. It is followed by a main verb. The structure is:

subject + must + main verb

The main verb is the base verb (infinitive without "to").

Look at these examples:

subject	auxiliary must	main verb
I	must	go	home.
You	must	visit	us.
We	must	stop	now.

Use of Must

In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary. Must is subjective. Look at these examples:

• I must stop smoking.
• You must visit us soon.
• He must work harder.

In each of the above cases, the "obligation" is the opinion or idea of the person speaking. In fact, it is not a real obligation. It is not imposed from outside.

We can use must to talk about the present or the future. Look at these examples:

• I must go now. (present)
• I must call my mother tomorrow. (future)

We cannot use must to talk about the past. We use have to to talk about the past.

Must not, Mustn't (prohibition)

We use must not to say that something is not permitted or allowed, for example:

• Passengers must not talk to the driver.

Structure of Must not

Must is an auxiliary verb. It is followed by a main verb. The structure for must not is:

subject + must not + main verb

The main verb is the base verb (infinitive without "to").

Look at these examples:

subject	auxiliary must + not	main verb
I	mustn't	forget	my keys.
You	mustn't	disturb	him.
Students	must not	be	late.

NB: like all auxiliary verbs, must CANNOT be followed by "to". So, we say:

• You mustn't arrive late. (not You mustn't to arrive late.)

Use of Must not

Must not expresses prohibition - something that is not permitted, not allowed. The prohibition can be subjective (the speaker's opinion) or objective (a real law or rule). Look at these examples:

• I mustn't eat so much sugar. (subjective)
• You mustn't watch so much television. (subjective)
• Students must not leave bicycles here. (objective)
• Policemen must not drink on duty. (objective)

We can use must not to talk about the present or the future:

• Visitors must not smoke. (present)
• I mustn't forget Tara's birthday. (future)

We cannot use must not to talk about the past. We use other structures to talk about the past, for example:

• We were not allowed to enter.
• I couldn't park outside the shop.

Shall versus Will

People may sometimes tell you that there is no difference between shall and will, or even that today nobody uses shall (except in offers such as "Shall I call a taxi?"). This is not really true. The difference between shall and will is often hidden by the fact that we usually contract them in speaking with 'll. But the difference does exist.

The truth is that there are two conjugations for the verb will:

1st Conjugation (objective, simple statement of fact)
	Person	Verb	Example	Contraction
Singular	I	shall	I shall be in London tomorrow.	I'll
	you	will	You will see a large building on the left.	You'll
	he, she, it	will	He will be wearing blue.	He'll
Plural	we	shall	We shall not be there when you arrive.	We shan't
	you	will	You will find his office on the 7th floor.	You'll
	they	will	They will arrive late.	They'll

 

2nd Conjugation (subjective, strong assertion, promise or command)
	Person	Verb	Example	Contraction
Singular	I	will	I will do everything possible to help.	I'll
	you	shall	You shall be sorry for this.	You'll
	he, she, it	shall	It shall be done.	It'll
Plural	we	will	We will not interfere.	We won't
	you	shall	You shall do as you're told.	You'll
	they	shall	They shall give one month's notice.	They'll

It is true that this difference is not universally recognized. However, let those who make assertions such as "People in the USA never use 'shall'" peruse a good US English dictionary, or many US legal documents which often contain phrases such as:

• Each party shall give one month's notice in writing in the event of termination.

Note that exactly the same rule applies in the case of should and would. It is perfectly normal, and somewhat more elegant, to write, for example:

• I should be grateful if you would kindly send me your latest catalogue.

Would

Would is an auxiliary verb, a modal auxiliary verb. We use would mainly to:

• talk about the past
• talk about the future in the past
• express the conditional mood

We also use would for other functions, such as:

• expressing desire, polite requests and questions, opinion or hope, wish and regret...

Structure of Would

subject + would + main verb

The main verb is always the bare infinitive (infinitive without "to").

	subject	auxiliary verb	main verb
+	She	would	like	tea.
		'd
-	She	would not	like	whisky.
		wouldn't
?	Would	she	like	coffee?

Notice that:

• Would is never conjugated. It is always would or 'd (short form).
• The main verb is always the bare infinitive.

Use of Would

would: Talking about the past

We often use would as a kind of past tense of will or going to:

• Even as a boy, he knew that he would succeed in life.
• I thought it would rain so I brought my umbrella.

Using would as as a kind of past tense of will or going to is common in reported speech:

• She said that she would buy some eggs. ("I will buy some eggs.")
• The candidate said that he wouldn't increase taxes. ("I won't increase taxes.")
• Why didn't you bring your umbrella? I told you it would rain! ("It's going to rain.")

We often use would not to talk about past refusals:

• He wanted a divorce but his wife would not agree.
• Yesterday morning, the car wouldn't start.

We sometimes use would (rather like used to) when talking about habitual past behaviour:

• Every weekday my father would come home from work at 6pm and watch TV.
• Every summer we'd go to the seaside.
• Sometimes she'd phone me in the middle of the night.
• We would always argue. We could never agree.

would: Future in past

When talking about the past we can use would to express something that has not happened at the time we are talking about:

• In London she met the man that she would one day marry.
• He left 5 minutes late, unaware that the delay would save his life.

would: Conditionals

We often use would to express the so-called second and third conditionals:

• If he lost his job he would have no money.
• IfI had won the lotteryI would have bought a car.

Using the same conditional structure, we often use would when giving advice:

• I wouldn't eat that if I were you.
• If I were in your place I'd refuse.
• If you asked me I would say you should go.

Sometimes the condition is "understood" and there does not have to be an "if" clause:

• Someone who liked John would probably love John's father. (If someone liked John they would probably love John's father.)
• You'd never know it. (for example: If you met him you would never know that he was rich.)
• Why don't you invite Mary? I'm sure she'd come.

would: Desire or inclination

• I'd love to live here.
• Would you like some coffee?
• What I'd really like is some tea.

would: Polite requests and questions

• Would you open the door, please? (more polite than: Open the door, please.)
• Would you go with me? (more polite than: Will you go with me?)
• Would you know the answer? (more polite than: Do you know the answer?)
• What would the capital of Nigeria be? (more polite than: What is the capital of Nigeria?)

would: Opinion or hope

• I would imagine that they'll buy a new one.
• I suppose some people would call it torture.
• I would have to agree.
• I would expect him to come.
• Since you ask me I'd say the blue one is best.

would: Wish

• I wish you would stay. (I really want you to stay. I hope you will stay.)
• They don't like me. I'm sure they wish I'd resign.

would: Presumption or expectation

• That would be Jo calling. I'll answer it.
• We saw a police helicopter overhead yesterday morning. | Really? They would have been looking for those bank robbers.

would: Uncertainty

• He would seem to be getting better. (less certain than: He seems to be getting better.)
• It would appear that I was wrong. (less certain than: It appears that I was wrong.)

would: Derogatory

• They would say that, wouldn't they?
• John said he didn't steal the money. | Well, he would, wouldn't he?

would that: Regret (poetic/rare) - with clause

This rare, poetic or literary use of would does not have the normal structure:

• Would that it were true! (If only it were true! We wish that it were true!)
• Would that his mother had lived to see him become president.

Should

Should is an auxiliary verb, a modal auxiliary verb. We use should mainly to:

• give advice or make recommendations
• talk about obligation
• talk about probability and expectation
• express the conditional mood
• replace a subjunctive structure

Structure of Should

subject + should + main verb

The main verb is always the bare infinitive (infinitive without "to").

	subject	auxiliary verb	main verb
+	He	should	go.
-	He	should not	go.
		shouldn't
?	Should	he	go?

Notice that:

• Should is invariable. There is only one form of should.
• The main verb is always the bare infinitive.

Use of Should

should: Giving advice, opinions

We often use should when offering advice or opinions (similar to ought to):

• You should see the new James Bond movie. It's great!
• You should try to lose weight.
• John should get a haircut.
• He shouldn't smoke. And he should stop drinking too.
• What should I wear?
• They should make that illegal.
• There should be a law against that.
• People should worry more about global warming.

should: Obligation, duty, correctness

Another use of should (also similar to ought to) is to indicate a kind of obligation, duty or correctness, often when criticizing another person:

• You should be wearing your seat belt. (obligation)
• I should be at work now. (duty)
• You shouldn't have said that to her. (correctness)
• He should have been more careful.
• Should you be driving so fast?

should: Probability, expectation

We use should to indicate that we think something is probable (we expect it to happen):

• Are you ready? The train should be here soon.
• $10 is enough. It shouldn't cost more than that.
• Let's call Mary. She should have finished work by now.

should: Conditionals

We sometimes use should (instead of would) for the first person singular (I) and first person plural (we) of some conditionals:

• If I lost my job I should have no money.
  (If he lost his job he would have no money.)
• We should be grateful if you could send us your latest catalogue.

This is not a very important distinction. (More about the use of shall/will and should/would.)

should: (If I were you I should...)

We often use the conditional structure "If I were you I should..." to give advice.

• If I were you, I should complain to the manager.
• If I were you I shouldn't worry about it.
• I shouldn't say anything if I were you.

Note that we can omit "If I were you..." and just say:

• I should complain to the manager.
• I shouldn't worry about it.
• I shouldn't say anything.

In these cases, the phrase "I should" really means something like "you should".

should: Pseudo subjunctive

We often use a special verb form called the subjunctive when talking about events that somebody wants to happen, hopes will happen or imagines happening, for example:

• The president insists that the prime minister attend the meeting.

However, this is much more common in American English. British English speakers would probably convey the same idea using should:

• The president insists that the prime minister should attend the meeting.

Here are some more examples:

Subjunctive typically American English	Using should typically British English
The president is insisting that pollution be reduced.	The president is insisting that pollution should be reduced.
The manager recommended that Mary join the company.	The manager recommended that Mary should join the company.
It is essential that we decide today.	It is essential that we should decide today.
It was necessary that everyone arrive on time.	It was necessary that everyone should arrive on time.

should: Why should..? | How should..?

If we don't understand (or agree with) something, we may use "Why should..?":

• Why should it be illegal to commit suicide? It's your life.

"Why should..?" and "How should..?" can also indicate anger or irritation:

• "Help me with this." | "Why should I?"
• "Where are my keys?" | "How should I know?"