The semicolon (;) has three main uses:
1) It can act as a hybrid of a comma and a period – just the way it looks! In this usage it connects two related but separate sentences without a conjunction.
Example: The rain came down; the rivers rose toward their banks.
2) A semicolon is also used before a conjunctive adverb (however, therefore, moreover, otherwise, thus, nevertheless). An exception is “whereas,” which is always preceded by a comma.
Example: It was raining very hard; consequently, I did not take my dog for his usual walk.
Note that there is no space before the semicolon, a single space after it, and the first letter of the next word is not capitalized unless it is a proper name.
3) A third usage of the semicolon is as a “super comma” to help organize a compound list of elements.
Example: The authors were John White, Arco; Jill Black, Texaco; and Roy Green, Vastar.
Here is a classic example of semicolon usage, which combines two of these three usages:
“It was the best of times, it was the worst of times; it was the age of wisdom, it was the age of foolishness; it was the epoch of belief, it was the epoch of incredulity; it was the season of Light, it was the season of Darkness; it was the spring of hope, it was the winter of despair; we had everything before us, we had nothing before us; we were all going directly to Heaven, we were all going the other way.” – Charles Dickens