Can and Could

Canandcouldare modal auxiliary verbs.

Can

Canis an auxiliary verb, a modal auxiliary verb. We usecanto:

  • talk about possibility and ability
  • make requests
  • ask for or give permission

Structure ofcan

The basic structure ofcanis:

subject / + / auxiliary verb
can / + / main verb

The main verb is always the bare infinitive (infinitive withoutto).

subject / auxiliary verb
can / main verb
+ / I / can / play / tennis.
- / He / cannot / play / tennis.
can't
? / Can / you / play / tennis?

Use ofcan

canfor possibility and ability

We usecanto talk about what is possible, what we are able or free to do:

  • Hecandrive a car.
  • Johncanspeak Spanish.
  • Icannothear you. (Ican'thear you.)
  • Canyou hear me?

Normally, we usecanfor the present. But it is possible to usecanwhen we make present decisions about future ability:

  1. Canyou help me with my homework? (present)
  2. Sorry. I'm busy today. But Icanhelp you tomorrow. (future)

canfor requests and orders

We often usecanin a question to ask somebody to do something. This is not a real question - we do not really want to know if the person is able to do something;actually, we want them to do it! The use ofcanin this way is informal (mainly between friends and family):

  • Canyou make a cup of coffee, please.
  • Canyou put the TV on.
  • Canyou come here a minute.
  • Canyou be quiet!

canfor permission

We sometimes usecanto ask or give permission for something:

  1. CanI smoke in this room?
  2. Youcan'tsmoke here, but youcansmoke in the garden.

(Note that we also usecould, may, mightfor permission. The use ofcanfor permission is informal.)

(Source: Englishclub.com)

Could

Couldis an auxiliary verb, a modal auxiliary verb. We usecouldto:

  • talk about past possibility or ability
  • make requests

Structure ofcould

subject / + / auxiliary verb
could / + / main verb

The main verb is always the bare infinitive (infinitive withoutto).

subject / auxiliary verb
could / main verb
+ / My grandfather / could / swim.
- / She / could not / walk.
couldn't
? / Could / your grandfather / swim?

Use ofcould

couldfor past possibility or ability

We usecouldto talk about what was possible in the past, what we were able or free to do:

  • Icouldswim when I was 5 years old.
  • My grandmothercouldspeak seven languages.
  • When we arrived home, wecould notopen the door. (...couldn'topen the door.)
  • Couldyou understand what he was saying?

We usecould(positive) andcouldn't(negative) for general ability in the past. But when we talk about one special occasion in the past, we usebe able to(positive) andcouldn't(negative). Look at these examples:

past
general / specific occasion
+ / My grandmothercouldspeak Spanish. / A man fell into the river yesterday. The policewere ableto save him.
- / My grandmothercouldn't speak Spanish. / A man fell into the river yesterday. The police couldn'tsave him.

Complete the sentences below; use can/can’t or could/couldn’t:

1. I ______sleep last night. It was so hot!

2. When I was five or six, I ______swim, but I ______now.

3. My late grandfather ______speak French. I ______speak anything but English.

4. We're having a dinner party next Saturday, but Bilal ______come.

5. When I met David last year, he ______swim. He was terrified of the water. Now he ______swim like a fish!

6. I ______finish my lunch today. I just wasn't hungry at all.

7. There are so many different ice creams to choose from. I ______decide. You choose for me.

8. I ______find Ben and then I found him in the garden. Now I ______find him again. He keeps disappearing!

Answers:

1. I couldn’t sleep last night. It was so hot!

2. When I was five or six, I couldn’t swim, but I can now.

3. My late grandfather could speak French. I can’t speak anything but English.

4. We're having dinner next Saturday, but Bilal can’tcome.

5. When I met David last year, he couldn’tswim. He was terrified of the water. Now he canswim like a fish!

6. I couldn’t finish my lunch today. I just wasn't hungry at all.

7. There are so many different ice creams to choose from. I can’t decide. You choose for me.

8. I couldn’t find Ben and then I found him in the garden. Now I can’t find him again. He keeps disappearing!