Talking about ability

The modal 'can' is a commonly used modal verb in English. It is used to express; ability, opportunity, a request, to grant permission, to show possibility or impossibility. It is this large amount of functions and the fact that ‘can’ is replaced by other modals when it is used to express future or past time that often lead to certain errors.

Here are some examples of 'can':

He can play the piano. Ability
We can visit my sister when we are in Brighton. Opportunity
You cannot (can't) use my car. Permission
Can I borrow your pen? Request
You can learn Japanese at that school. Possibility

Can – present – past – future

Like most modal verbs 'can' is very different in the past or future. Here is how 'can' is used in different situations.

Ability

Present I can play the piano / I can't play the violin
Past (could) I could play the piano as a child. / I couldn't play the violin as a child.                                       
Future I will be able to play the piano soon / I won't be able to play the violin.

When referring to ability during a specific event 'was able to' replaces could:
With my friend's help, we were able to clear the garage in no time at all.

Opportunity

Present I'm free now. We can go. / I'm not free now. We can't go yet.
Past (be able to) I was free so we were able to go. / I was not free so we were unable to go.
Future I'll be free then so we can go. / I won't be free then so we can't go.

Permission

Present I can stay at Danny's when he's out of town. / I can't stay at Danny's when he's out of town.
Past I was allowed to stay at Danny's when he was out of town. / I wasn't allowed to stay at Danny's when he was out of town.
Future  I can stay at Danny's when he's out of town next month. / I can't stay at Danny's when he's out of town next week.

With permission 'may' is also used although this is seen as more formal.

Request

Present Can I have a coffee? / Can't I have a coffee?

With requests the time is usually the near future. 'May' or 'could' are also possible.

Possibility

Present You can earn a lot of money in gaming. / You can't earn a lot of money as a teacher

Possibility with 'can' is normally used for generalisations. 'Could' is also possible.

Talking about ability

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How to express ability

To express that someone has the power or skill to do something, can and be able are used.
Examples:

• I can't help you.I am busy.
• I'm unable to help you.
• When I was young I was able to earn my living pretty well; I could work hard. Now I can't. I'm too old.
• I can stand on my head for five minutes.
• Can you speak Arabic?
• Yes, I can.

Expressing ability

In the present:

Express ability in the present as follows:

• I can speak good English.
• I can't stand on my head.

In the past

Express ability in the past as follows

• I was unable to visit him.
• I couldn't eat at all when I was ill.

In the future

Express ability in the future as follows

• I will be able to buy a house when I get a good job.
• The teacher can assist you after class if you have any questions.

Things to remember:

• Can is always followed by an infinitive without "to."
  Examples:
  I can ride my bike and I can drive a car, but I can't drive a lorry.
• Can in the past is was able or could
  Examples:
  When I was young I was able to earn my living pretty well. Now I can't; I'm too old.
  I couldn't hear what he was saying.
• Can in the future is will be able.
  Example:
  When I finish my studies, I will be able to find a job.

Asking For And Giving Permission

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Asking for and giving permission:

When you ask for permission to use something that belongs to someone else you have to do your best to be polite. It is desirable to use the word "please."

Asking for Permission:

• Can I go out, please?
• May I open the window, please?
• Please, can I have a look at your photo album?
• Please, may I taste that hot spicy couscous dish?
• Do you mind if I smoke?
• Would you mind if I asked you something?
• Is it okay if I sit here?
• Would it be all right if I borrowed your mobile Phone?

Giving Permission:

• Yes, please do.
• Sure, go ahead.
• Sure.
• No problem.
• Please feel free.

Refusing to give permission:

• No, please don’t.
• I’m sorry, but that’s not possible.
• I'm afraid, but you can't.

Dialogue:

Liza, eight years old, is asking her mother for permission to use the computer...

Liza:	Please mum, can I use the computer?
Her mother:	No, dear you can't. It's time to go to bed.
Liza:	May I read a story before I sleep?
Her mother:	Sure! But try to sleep early.
Liza:	Thanks a lot mummy.