3C

Can

It is an auxiliary verb, a modal auxiliary verb. We use it to:

·         Talk about possibility and ability

·         Make request

·         Ask for or give permission

·         It only has a present, past, and conditional form. ­

Estructure of can: subject + can + main verb

The main verb is always the bare infinitive (infinitive without “to”)

	Subject	Auxiliary verb	Main verb
+	I	can	swim
-	She	cannot	Swim
		can´t
?	Can	you	swim?

Could

It is an auxiliary verb, a modal auxiliary verb. We use it to:

·         Talk about past, possibility or ability

·         Make requests

Structure of could: subject + could + main verb

	Subject	Auxiliary verb	Main verb
+	My sister	could	swim
-	I	could not	Swim
		couldn´t
?	Could	you	swim?

Notice that:

·         Could is a variable. There is only one form of could.

·         The main verb is always the bare infinitive.

Be able to + base form

It is not a modal verb. It is simply the verb be plus an adjective (able) followed by the infinitive. We sometimes use it instead of can and could.

You can use be able to in the present, past, future, present perfect, and as a gerund or infinitive.

Be able to in the present and past is more formal than can/could.

We use be able to:

·         To talk about ability

Structure of be able to: subject + be + able + infinitive

	Subject	Be main verb	Able adjective	Infinitive
+	I	am	able	to drive
-	he	Is not	able	to drive
		Isn´t
?	Are	you	able	to drive

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

·         She was able to work…

·         He will be able to go…

·         I have been able to play…

Notice too that be able to has an infinitive form:

·         I would like to be able to speak French.