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 is not a modal auxiliary verb. We include it here for convenience, because it is often used like "can" and "could", which are modal auxiliary verbs.

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)

Auxiliary Verbs "Can/Could" and "May/Might/Must"

Can

Used to express ability (to be able to do something):

• I can make jewelry.
• He can’t speak French.
• Can you open this jar?

Used to ask for permission:

• Can I use your bathroom?
• Can I leave now?
• Can I raise the volume?

Used to make requests or suggestions:

• Can I have more napkins?
• Can I have the bill?
• You can take this spot if you like.
• You can do whatever you want.

Could (past form of can)

Describes an ability that someone had in the past:

• I could swim when I was young.
• You could see the boat sinking.
• They could tell he was nervous.

Often used in auxiliary functions to express permission politely:

• Could I take this jacket with me?
• You could borrow my umbrella.
• Could you please let me pass you?
• Could I get you more water?

Used to express possibility:

• All of them could ride in the van.
• You could always stay at our house.
• Could it be true?
• This plan could really work out.

May

Used to ask for formal permission:

• May I come in?
• May I say something now?
• May I ask one question?

Used to suggest something that is possible:

• She may agree with this plan.
• They may not be happy about what happened.
• It may shower tonight.

Might (past form of may)

Used to suggest a smaller possibility than may does (actually, might is more common than may in American English):

• He might have finished it.
• I might go see a doctor.
• I might not come this time.
• It might be right.
• You might have lost it.
• The store might have been closed today.

Must

Used to express something formally required or necessary:

• I must complete the project by this week.
• The government must provide health care for everybody.
• Everyone must save the natural resources of the earth.
• The building must have a fire alarm.
• You must answer my question right now.

Used to show that something is very likely:

• He must be a genius.
• You must be joking!
• There must be an accident.
• She must be very tired.

[Quiz 21.1]

Choose the right word for each blank.

1) She                      (can, could, may, might, must) have practiced a lot. Her performance was amazing.
2) I can’t find my watch anywhere. I                      (can, could, may, might, must) have lost it.
3) Professor,                      (can, could, may, might, must) I ask a question?
4)                      (can, could, may, might, must) you please lower your voice?
5) You                      (can, could, may, might, must) be kidding! How is that possible?
6) I                      (can, could, may, might, must) speak both English and Chinese fluently.