Modal "could"

Question

I have a question about past abilities with could.

It is my understanding that if I want to talk about ability at one specific moment in the past, I can’t use could. I have to use the phrasal modal “be able to” instead. Is this correct?

Could you please look at these sentences?

I could dance when I was young. CORRECT unspecified time in the past (?)

I could dance yesterday. INCORRECT one specific moment in the past. I shouldn’t use could (?)

I was able to dance yesterday. CORRECT one specific time in the past (?)

I could dance on Monday, December 01, 2020. INCORRECT one specific moment in the past. I shouldn’t use could (?)

I was able to dance on December 01, 2020. CORRECT one specific moment in the past (?)

Which of these sentences are correct?

Am I correct on my understanding of "could" to talk about past abilities? Please let me know.

AlpheccaStars · Accepted Answer

These are all sentences that I might use in conversation.

I could dance like a professional ballerina when I was young.
I could dance yesterday, but not today. I broke my big toe last night.
I was able to dance yesterday, but not today. I broke my big toe last night.
I could dance on Monday, December 01, 2020, but not on Tuesday December 2. I had broken my big toe.
I was able to dance on December 01, 2020.

CalifJim · Answer

apatzinguenseIt is my understanding that if I want to talk about ability at one specific moment in the past, I can’t use could. I have to use the phrasal modal “be able to” instead. Is this correct?

It's not exactly ability in the past. It's more that you can't express success in the past with 'could'.

Your examples show that you are focusing too much on exact moments (specific times) in contrast to unspecific times. That isn't exactly how this works, except for the fact that success usually happens at some exact moment.

Suppose you had to run in order to catch a bus.

I ran fast, and I was able to catch the bus. This is correct. Because you ran fast, you were able to catch the bus. You succeeded in getting on the bus. You were not left behind because you missed the bus.

It is wrong to say I ran fast, and I could catch the bus if you mean that you succeeded in catching the bus.

However, you can use could correctly in the following sentences.

When the bus schedules were different, if I missed the bus at Maple Street, I could always catch the bus at Elm Street. (It was always possible to do this. The opportunity was always there to try taking such a course of action. It doesn't mean "I always succeeded at catching the bus at Elm Street".)

— How do I get to the Sears Tower?
— You could take a taxi, or you could catch the bus.
(Again, this has to do with having opportunities, not with success.)

Before I broke my leg, I could easily catch the bus by running.
(I had that ability. The sentence doesn't say that I succeeded in doing that on any specific occasion.)

Note: None of this applies to "could not", which is fine when it means "failed" ("did not succeed").

Although I ran very fast, I couldn't catch the bus. OK.
Although I ran very fast, I wasn't able to catch the bus. OK.

Both ways are OK.

CJ

Modal "could"

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