- "Dan was so successful at school, he made it, he could."
Can the modal verb "could" be used as in the above example, as a standalone without a verb following it?
- "Dan was so successful at school, he made it, he could (do it)."
You can use could without a verb following like all modal verbs, but the context should make sense. Could should only be used if the sentence is expressing ability to do something and is conditional.
Could infers that one can do it now and after, but you used the past-tense of to be (was).
Here's an example which would work.
Person 1: He could make the team if he tries harder.
Person 2: In my opinion, I don't think he could.
As a simple answer to your question, yes, you could.