How to use 'could'

Question

I actually called her, but before I could finish my sentence she cut me off and told me that she was pregnant.

In this sentence, I can't understand why 'could' is needed. How about just 'finished'?

Answer 1

Could refers, in this sense, to possibility or capability.

Using "…before I finished…" also makes sense, as it would clearly be what happened, but "…before I could…" means that it was not just before you finished, but before it was even possible for you to finish.

In some cases there's a bigger difference; "There was a test before I studied the material" might be because I procrastinated for two months while "There was a test before I could study the material" is not my fault.

With something like finishing a sentence, it amounts to the same thing in practice, but still emphasises how quickly she spoke and that it wasn't your fault you hadn't finished.