Grammar Basics: Unit 31 – can and could

“can” is used to indicate the ability to do something. It is used with a verb in the infinitive form:

can + V (inf.) …

Examples:

I can play the piano.
Shelia can ride a bike.
The twins can play chess.
We can go to the museum tomorrow.

Note: “can” is the same, regardless of person and number. First person singular, third person plural – it doesn’t matter :).

To make a question, switch the order of “can” and its subject:

Can you play the piano?
Can Jack ride a bike?
Can they play checkers?

To negate, put “not” between “can” and its verb: “can not”, which is written as one word ==> “cannot”

I cannot lift this heavy suitcase.
They cannot come because of bad weather.
Sam cannot speak Chinese.

Note: “cannot” is usually contracted to “can’t.” Thus we have:

I can’t lift this heavy suitcase.
They can’t come because of bad weather.
Sam can’t speak Chinese.

All the examples we’ve given thus far use “can” or “can’t” in the present or future tense. To speak of ability in the past tense, we use “could” (“could not” or “couldn’t” for the negation):

The neighbors were noisy, so I couldn’t sleep at all last night.
James could eat a whole pizza when he was a teenager.
They could stay up all night when they were in college.

Other Notes:

1) Sometimes “can” / “can’t” is used for permission rather than ability:

You can’t use your cell phone in the library.
Tom can’t go visit Becky. He has to whitewash the fence.
Can I have a drink of water?

2) In asking permission, “could” is a more polite form to use than “can”:

Can I have a drink of water? ==> Could I have a drink of water?
Can my friend sit here? ==> Could my friend sit here?
Can you open the window? ==> Could you open the window?


Exercises:

Using the given clues, write sentences using “can.” If there is a question mark, make a question using “can.”

Example:

Tom / sing well ==> Tom can sing well.
She / speak Italian / not ==> She can’t speak Italian.
John / poker / ? ==> Can John play poker?

1. Walter / drive / a car
2. We / come / to the party / not
3. I / ice skate
4. You / swim / ?
5. Bill / go / to the picnic
6. We / go on vacation / this summer / ?
7. They / buy a house / not
8. You / shut / the window / ?
9. Sally / cook / dinner
10. Tim / stay up / late / not

Determine whether to use “can” or “could” with the given verb in the following sentences.

Example:

I wasn’t busy, so I (come) to the party. ==> I wasn’t busy, so I could come to the party.
Dan is sick. He (go, not) to the football game. ==> Dan is sick. He can’t go to the football game.

1. After eating a whole pizza, James was full. He (eat, not) another bite of food.
2. Louis is blind. He (read, not) that book.
3. Mark is in high school, so he (attend) summer camp this year.
4. We (go, not) swimming at the outdoor pool because there was a thunderstorm.
5. We have finished packing, so we (leave) on our trip as soon as you’re ready.
6. John didn’t finish his homework in time, so he (go, not) skiing with us.
7. On a clear day, you (see) forever.
8. We had an extra seat in the car, so we (give) Mary a ride to the train station.
9. If you’re tired, you (take) a quick nap before dinner.
10. The weather was nice, so we (go) camping at the state park last weekend.