What Are Semi-colons?

A semi-colon is used to join two independent clauses (that make sense on their own) together.

For example:

Jim went to the gym. He took his swimming goggles.

Jim went to the gym he took his swimming goggles.

Incorrect example:

Jim went to the gym but he forgot his swimming goggles.

Jim went to the gym but he forgot his swimming goggles.

This is incorrect as `but he forgot his swimming goggles` is a dependent clause, as it doesn`t make sense on its own without the information at the beginning.