Can and Be Able To

 

Modal verbs are helping¹ verbs. We use them with main verbs to help us express ability, possibility, necessity² and permission. Today’s question is about a modal that is commonly confused with an expression. Here’s the question, which comes from a listener named Cafer:

Question

Hi! Would you like to explain the difference between “can” and “be able to”? Thank you. -Cafer ?zcan?

Answer

Hi, Cafer!

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

“Can” is a modal verb. We use it to:

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:

ask for or give permission?

I am finished. Can I go now?

Yes, you can.

and to ask someone to do something?

Can you bring me the magazine?

Be able to

Now, let’s explore “be able to.”

This expression is not a modal. It is the verb “to be” plus the adjective³ “able.” The word “to” shows that an infinitive⁴ verb will follow.

We use “be able to”:

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."

And that’s Ask a Teacher.

I’m Alice Bryant.

Words in This Story

confuse – v. to make someone unable to understand something

guitar – n. a musical instrument that is held against the front of your body and that has six strings⁵

infinitive – n. the basic form of a verb

negative – adj. describing a word or statement that means “no” or that expresses a denial or refusal

1 helping   

n.食物的一份&adj.帮助人的，辅助的

参考例句：

• The poor children regularly pony up for a second helping of my hamburger. 那些可怜的孩子们总是要求我把我的汉堡包再给他们一份。
• By doing this, they may at times be helping to restore competition. 这样一来, 他在某些时候,有助于竞争的加强。

2 necessity   

n.必要性，需要；必需品

参考例句：

• I look upon this as an absolute necessity.我认为这是绝对必要的。
• You must understand the necessity of education.你必须懂得教育的必要性。

3 adjective   

n.形容词；adj.形容词的，用作形容词的

参考例句：

• Don't apply that adjective to me.不要用那个字眼来形容我。
• The adjective loose has several senses. 形容词loose有几个义项。

4 infinitive   

n.不定词；adj.不定词的

参考例句：

• The use of the split infinitive is now generally acceptable.分裂不定式的用法现在已被广泛接受。
• Modal verbs generally take the bare infinitive.情态动词通常用不带to的不定式。

5 strings   

n.弦

参考例句：

• He sat on the bed,idly plucking the strings of his guitar.他坐在床上，随意地拨着吉他的弦。
• She swept her fingers over the strings of the harp.她用手指划过竖琴的琴弦。