Could/be able to

[Rachel Adams]

Hello.

This exercise is from Longman. It asks to use suitable forms of be able to.

Is it possible to use 'could' in the first and fifth sentences?

1. 'I have been trying for hours , but so far I haven't been able to get through on the phone.'

2. 'I am sure she would have helped you if she had been able to.'

3. 'If I had been able to sing, I would have loved to be an opera singer.'

4. 'He has managed to live in England for years without being able to speak English.'

5. 'It took a long time, but in the end Tony was able to save enough to buy his own hi-fi.'

 

[GoesStation]

I wouldn't be astonished to hear a native speaker use couldn't in number one, but I would not recommend it. Could doesn't work in number five.

You didn't ask about the others, but could is possible for me in two and three.

 

[Rachel Adams]

No.
No.

The difference between 'could do' and 'could have done' is confusing because both are past forms. What is the main difference between them? If the first sentence didn't have the present perfect, would 'could' work? For example, 'I was trying for hours but I couldn't get through on the phone.'

 

[Rachel Adams]

That works.

So 'could have +past participle is used with perfect only. Right? If I am talking about a recent past action. For example, 'What was that noise?' It could have been a cat.' 'It could be a cat' is wrong. This example is from Swan.

 

[Rachel Adams]

'It could be a cat' is not necessarily wrong.

'It could have been a cat' suggests that there is a possibility that it was a cat that caused the noise.
'It could be a cat' suggests that there is a possibility that there is a cat around (and the logical extension is that it is this hypothetical cat that caused the noise).

You said 'there is a cat' when you used 'could' so you don't use 'could' when something was possible in the past. Instead you use 'could have + past participle. That's probably the main difference between 'could' and 'could have +past participle.'