1. He came back after a week.

Question

2. He came back in a week.
3. He will be back after a week.
4. He will be back in a week.
[Which onea are incorrect? What abe the differences?]

Answer 1

In these sentences, “in” seems to mean “within” — meaning before a full week.

In these sentences, “after” means 8 days or more.