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Physical or mental ability; capability

(this meaning is also expressed by to be able)

He can run very quickly.

I can't play chess.

Can usually expresses an action referring to the present. In some contexts, however, it may express actions referring to the future:

I think I can help you afterwards.

If the time reference is not clear to be able is used:

I'll be able to help you.

A real action in the past is expressed by could (past indicative) and the simple infinitive:

He could speak English when he was a boy.

An unreal imaginary action referring to the present is expressed by could (Subjunctive II present) and the simple infinitive; to the past – by could and the perfect infinitive:

She could answer this question now.

She could have answered this question then.

Note 1. Could is not used to describe the successful completion of a specific action; was / were able to, managed to or succeeded in must be used instead:

In the end they were able (managed) to rescue the cat on the roof. or … succeeded in rescuing… (L.G.Alexander)

If the action was not successfully completed we may use couldn't:

They tried for hours, but they couldn't rescue the cat. (L.G.Alexander)

Note 2. Can is often used with the verbs of physical perception and with the verb to understand:

I can hear somebody knocking at the door.

He can't understand what we are talking about.

Possibility due to circumstances (in all types of sentences)

You can get to the centre on foot.

You can't get to the centre on foot.

Can I get to the centre on foot?

Permission (in affirmative and interrogative sentences)

You can take my dictionary.

Can I take your dictionary?

Note. To make asking for permission more polite could is used:

Could I take your dictionary?

Prohibition (in negative sentences)

You can't take my things without permission!


Date: 2015-04-20; view: 1194


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