The context is a comparison between Bach and a certain twentieth century composer who only wrote 50 minutes of music for quartet in his entire career. Although it is an event in the past, nobody knows exactly how Bach spent his days and how much music he wrote on any given one. What I want to say is that I believe he was capable of writing more than 50 minutes of music on a good day. "I suspect there were many weeks when Bach wrote more than fifty minutes of music. Perhaps he could do it on a good day." Is that "could do it" a good form to use or is there a better?

1 Answer 1


In this situation, I would recommend using could have done.

As described on englishgrammarsecrets.com, this construction often describes something in the past in a speculative way. The third of the examples provided is especially similar to your case, in that it clearly speculates on what might have happened in the past, as opposed to proposing a hypothetical alternative to what is known not to have happened.

We can use 'could have' to speculate about what has happened. (We can also use 'may have' or 'might have' in these situations.)

She could have taken the earlier train.

Simon could have told her.

They could have overheard what we said.

This downloadable PDF published by Cambridge University Press does a good job explaining the difference between "could do" and "could have done.

As the first link explains, you could also write "may have" or "might have."

Perhaps he could have done it on a good day.

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