4.113 ability in the past: 'could'

'Could' can be regarded as the past tense of 'can' if you are simply talking about the ability of a person or thing to do something.

For example, if you are talking about a living person, you can say 'He can speak Russian and Finnish'. If you are talking about a dead person, you can say 'He could speak Russian and Finnish'.

For a fuller explanation of these uses see paragraphs 4.119 to 4.121.