can / be able to — Be Able To

can and be able to express ability or possibility, meaning “be able to do something.” At the junior high school level, can is central, while be able to plays a supplementary role.

Basic Rules

Since can is a modal verb, it is followed by the base form of a verb (× I can plays → ○ I can play). Its form does not change even with a third-person singular subject (× He cans → ○ He can). The negative is cannot / can't, and the question word order is Can + subject + base form of the verb? In addition to ability, it can express permission (“may do ~”) and a request (“could you do ~?”).
be able to has the form the verb be + able to + the base form of a verb and expresses ability like can. The difference is that it can be combined with the future and perfect forms (will be able to / have been able to). can has only present and past (could) forms.

Points to Note

① The verb after a modal verb must always be in its base form. The third-person singular s is unnecessary, and the -ing and past forms are also incorrect. “She can swims.” and “He can swimming.” are both incorrect.
② For permission and requests, Could / May are more polite than can. Remember “Could you help me?” and “May I use ~?”
③ Past ability: use could for “was able to do something in the past.” For something actually accomplished at a particular time in the past, was/were able to is often used: “I could swim when I was five.” (ability) and “I was able to finish the race yesterday.” (accomplishment).

Practice

1. Write “Can she play the guitar? — Yes, she can” in English.
2. Write “I will be able to drive a car next year” using be able to.
3. Correct the error: He cans plays the piano.