The semicolon has always been a nuisance to me. I never really learned its purpose or when to use it; therefore, this rhetorical device was most appealing to me to research. A semicolon is a punctuation mark that causes the reader to notice the relationship between ideas without explicitly being told by the writer. The semicolon was invented by Aldus Manutius to separate words with different meanings. The first time that it was used regularly was in 1560 by Henry Denham. Then in 1591 the more general use of the semicolon was often done by Shakespeare.
I personally have misused semicolons and neglected to use them when needed many times. If you look closely, you may actually find some of my semicolon mistakes. One example is that I have used a comma instead of a semicolon (i.e. I was late for to the movies, I take long showers.) The comma should have been substituted with a semicolon to represent a longer pause and to relate two independent clauses. Another way to use a semicolon is to separate the items/people/places of complicated list: There were citizens from Bangor, Maine; Hartford, Connecticut; Boston, Massachusetts; and Newport, Rhode Island. Commas had to be used to show that the cities belonged to their respective states; therefore semicolons had to be used to separate each place in the list. The semicolon is also used in cases like this: My grandmother seldom goes to bed this early; she's afraid she'll miss out on something. It started as two separate sentences, but with the use of a semicolon, they can combine to form a single sentence with two separate clauses. a comma could have been used with an additional word like "so" after the comma, but with the use of the semicolon, the writer can show a relationship without explicitly showing it.

References:

1) http://grammar.ccc.commnet.edu/grammar/marks/semicolon.htm

2) http://www.auburn.edu/academic/liberal_arts/english/ec/resources/semicols.htm