Past ability and possibility

Past ability & possibility

 

In the present tense we use ‘can’ to talk about a general ability – e.g. I can swim – and also for ability at a particular moment – e.g. I can see you! The rules for talking about past abilities are different.

General ability

We use could to talk about general abilities in the past.

• He could speak fluent French when he was 5.
• I could read before I started school.

Ability on one occasion

However, when we talk about ability on one particular occasion, we can’t use could

• The burglar was able to get in through the bathroom window.
• The burglar managed to get in through the bathroom window.

We have to use was able to or managed to. We can’t use could.

• The burglar could get in through the bathroom window.

Ability on one occasion - negative

When we talk about a particular occasion when something wasn’t possible, we can use wasn’t/weren’t able to, didn’t manage to, or couldn’t

• The burglar wasn’t able to get in through the window.
• The burglar didn’t manage to get in through the window.
• The burglar couldn’t get in through the window.

Hypothetical past ability

Sometimes things were possible in the past but didn’t happen.

• I could have gone to university but I decided to get a job.
• I would have been able to win the race but I fell over.

We use could have (+ past participle) or would have been able to to talk about these hypothetical events. They can be used in the positive and the negative.

• I couldn’t have done it without your help.
• I wouldn’t have been able to afford it even if it had been for sale.

- See more at: http://learnenglish.britishcouncil.org/en/grammar-reference/past-ability-possibility#sthash.JddrcE1x.dpuf

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