The Use of Semicolons

A semicolon should be used when writing two independent clauses as one sentence. For example:

Stephen King's books are horrific; they are so well written. 

It is nearly half past five; we cannot reach town before dark.

These sentences can also be written as two separate sentences:

Stephen King's books are horrific. They are so well written.

It is nearly half past five. We cannot reach town before dark. 

If a conjunction is inserted, then the proper mark is a comma:

Stephen King's books are horrific, for they are so well written. 

It is nearly half past five, and we cannot reach town before dark.