Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

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539 Glossary for any unfamiliar terms

Modality | 643

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The expression how could you is often used to indicate disapproval or to issue a

reproach:

How could you forget that we’re going out to dinner tonight?

‘You have quite ruined our day. 

How could you?’ she sobbed. ‘How could you?’

Past tense of can

Could

is used as the past tense form of can when clauses with can are reported as

past events:

In tennis I wasn’t that good but I knew I 

could get better.

(at the time, the speaker thought ‘I know I can get better’)

(In tennis I wasn’t that good but I knew I can get better.)

When I was a kid I 

couldn’t swim at all. I only learnt when I was thirty.

They said we 

could do whatever we wanted.

We 

could hear that dog barking all through the night.

However, when actual achievements are indicated, was/were able to, not could,

is preferred in past affirmative clauses. The negative forms couldn’t or wasn’t/

weren’t able to

are both used to indicate non-achievement:

The thieves escaped but the police 

were able to arrest them later that evening.

(The thieves escaped but the police could arrest them later that evening.)

[talking about a live concert by the Beatles in the 1960s]

Sharon and I 

were able to get special seats but we couldn’t hear a thing. The

screaming was just something else. There were kids fainting, and being taken

out, everything. 

She 

was not able to move on her own.

(or: She couldn’t move on her own.)