Modals of Ability: Can, Could, Be able to, May, Might

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”.

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.

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:

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.

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:

Notice that we do not “contract” may + not = mayn’t. Wrong!
Can’t and couldn’t are common contractions, however.