Can and can't

When you use it

You use can to say what someone is able to do (I can swim), what is possible or allowed (you can park here after six), and to ask for something or offer something (Can you help me?, Can I open the window?). Can't is the negative for all of these: no ability, not possible, not allowed. Can is a modal verb, and modal verbs follow their own small set of rules that make them simpler than ordinary verbs.

How it is formed

Can has one form for every subject. It never takes -s, it is followed by the base form of the verb without to, and it makes its own negative and question without do.

The negative is written cannot as one word, or can't in the short form. Short answers use can or can't alone: Can you swim? Yes, I can. No, I can't.

Wh-questions keep the same order with the question word in front: What can you see?, When can we start?, How can I help you?

In speech the two forms are told apart mainly by the vowel. Can is usually unstressed and short, /kən/. Can't is stressed and long, /kɑːnt/ in British English and /kænt/ in American English. If you stress can heavily, a listener may hear the negative.

Can has no infinitive and no future form. To talk about ability in the future you use will be able to: I will be able to drive next year. For the past, could is the usual form: I could swim when I was five. Could is also a more polite version of can in requests: Could you help me?

Examples

• I can swim, but I can't dive.
• Anna can speak three languages.
• Tom can't drive yet. He is taking lessons.
• Can you help me with this box?
• You can park here after six o'clock.
• We can't hear you. Please speak louder.
• Can I open the window?
• Birds can fly, but penguins can't.

Common mistakes

• ✗ She cans swim. He can swims.
  ✓ She can swim.
  Neither can nor the verb after it takes -s. In Ukrainian and Russian вміє / умеет and може / может change for the person, so learners look for an ending somewhere. There is none.
• ✗ I can to swim. Can you to help me?
  ✓ I can swim. Can you help me?
  After можу / могу the Slavic verb is in the infinitive, плавати / плавать, and the English infinitive is usually to swim. But after a modal verb the to disappears. This is true of all modals: can swim, must go, should stay.
• ✗ Do you can help me? I don't can come.
  ✓ Can you help me? I can't come.
  Can is its own helper. It moves in front of the subject to make a question and takes not directly to make a negative. Adding do gives the sentence two helpers.
• ✗ I can not swim. I cann't swim.
  ✓ I cannot swim. I can't swim.
  The full negative is one word, cannot. The short form is can't with one n. Can not as two words is only used when not belongs to something else, as in I can not only swim but also dive, which is a different structure.
• ✗ I can't hear nothing. She can't find nobody.
  ✓ I can't hear anything. She can't find anybody.
  Can't is already negative. Ukrainian and Russian add a second negative word (нічого не чую / ничего не слышу); English switches to anything, anybody, anywhere.

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