I get ahead of myself. Nowadays, computer-users type the semi-colon far less frequently to punctuate than to join a parenthesis to create a winky face. A definition is required: Strunk and White explain the semi-colon in their book, The Elements of Style, to illustrate their point titled, "Do not join independent clauses with a coma, "If two or more clauses grammatically complete and not joined by a conjunction are to form a single compound sentence the proper mark of punctuation is a semi-colon." The authors give, "It is nearly half past five; we cannot reach town before dark," as an example. A semi-colon belongs between two clauses that could be two independent sentences ("It is nearly half past five. We cannot reach the town before dark.") or two clauses joined by a conjunction preceded by a coma (It is nearly half past five, and we cannot reach the town before dark.). Or one can imagine an observation that links the two sentences ("It is half past five, and I fear we cannot reach the town before dark."). Strunk and White go on to write that the semi-colon "suggests a close relationship between the two statements in a way that [making them two sentences] does not attempt, and better than [inserting a coma and conjunction] because it is briefer and therefore more forcible."
The semi-colon gives nuance to written expression in the most succinct way; I may over-use it, for, as Strunk and White observe "the relationship [between the two clauses] is commonly one of cause and consequence."
