oxford_guide_to_english_grammar

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99 Unreal situations: would
But we normally use can to suggest a possible future action. • 97(2a)
We can discuss the details later.
3 Could and was/were able to
a
b
In the past, we make a difference between a general ability and an ability which
resulted in an action. For a general ability we use could or was/were able to.
Kevin could walk/was able to walk when he was only eleven months old.
But we use was/were able to to talk about an action in a particular situation, when
someone had the ability to do something and did it.
The injured man was able to walk to a phone box.
NOT The injured man could walk to a phone box.
We can also express the meaning with managed to or succeeded in.
Detectives were able to/managed to identify the murderer.
Detectives succeeded in identifying the murderer.
But in negatives and questions we can use either was/were able to or could because
we are not saying that the action really happened.
Detectives weren't able to identify/couldn't identify the murderer.
Were you able to get/Could you get tickets for the show?
NOTE
It is safer to use was/were able to when the question with could might be understood as a
request. Could you get tickets? can be a request meaning 'Please get tickets'.
c
d
We normally use could (not was/were able to) with verbs of perception and verbs of
thinking.
I could see smoke on the horizon.
We could understand that Emily preferred to be alone.
To say that someone had the ability or the chance to do something but didn't do it,
we use could have done.
He could have walked there, but he decided to wait where he was.
I could have got tickets, but there were only very expensive ones left.
NOTE
Could have done can also express a past action that possibly happened. • 97(3)
The murderer could have driven here and dumped the body. We don't know yet if he did.
e
Could can also mean 'would be able to'.
I couldn't do your job. I'd be hopeless at it.
The factory could produce a lot more goods if it was modernized.
99 Unreal situations: would
1 Compare these sentences.
We're going to have a barbecue. ~ Oh, that'll be nice.
We're thinking of having a barbecue. ~ Oh, that would be nice.
Here will is a prediction about the future, about the barbecue. Would is a
prediction about an unreal situation, about a barbecue which may or may not
happen.