Modal verbs are helping verbs. We use them with main verbs to help us express ability,
possibility, necessity and permission. Today’s question is about a modal that is commonly confused with
an expression.
Would you like to explain the difference between “can” and “be able to”? Thank you.​
I can explain the differences between the two.
I just used “can” to talk about my ability to do something. We also use “be able to”
for abilities, but usually only when “can” is not possible. I’ll tell you what that
means in a minute. But first, let’s explore the word “can.”
“Can” is a modal verb. We use it to: 1. talk about present or future ability or
possibility I can play the guitar.
You can buy the tickets online. You must use “could” for the past tense,
such as in, “You could have bought the tickets online.”
We also use “can” to: 2. ask for or give permission​
I am finished. Can I go now? Yes, you can.
3. and to ask someone to do something​ Can you bring me the magazine?
Now, let’s explore “be able to.” This expression is not a modal. It is the
verb “to be” plus the adjective “able.” The word “to” shows that an infinitive verb
will follow. We use “be able to”:
1. when it is not possible to use “can” for abilities, such as after other modal verbs​
I won’t be able to take you to the train station. Sorry!
You should be able to finish the book in a few days.
The words “won’t,” short for “will not,” and “should” are modals. In English,
we do not put two modals together. So, we cannot put “can” after them.
We also use “be able to”: to talk about small or large past successes.
​ We were able to get a great price on the television.
She was able to win the math competition last month.
But in negative form, we can use "be able to” or “could”:​
We couldn’t get a great price on the television. She wasn’t able to win the math competition
last month. But note that the negatives "wasn’t able
to" and "weren’t able to" are a little more formal than "couldn't."