When Should I Use Semi-Colons? - Punctuation for Meaning
ere are two basic rules for the use of semic-colons:
A semi-colon is placed between two independent clauses.
Procrastination doesn't have to happen; a writer must
decide to delay.
Note that two, shorter sentences can be joined by a comma. For
He started early, success soon followed.
A semi-colon is placed before a conjunctive adverb (however,
thus, therefore, consequently, etc.) when it is used to join two
sentences (independent clauses). For example,
I wanted to start writing sooner; however, I never quite
got around to it.
Note that a comma is placed after a conjunctive adverb.
For a more detailed and more formal explanation, see The New
Century Handbook or a similar source.