If you never properly grasped the correct usage of the semicolon or colon in school it might have been because your English teacher was really there to coach volleyball. But it might also be because many, many people debate correct usages. Many famous and talented authors use, even idolize, those marks. Others, equally famous and talented, think that their use will precipitate the end of the world. So, if you never gained proper command of them, it may just be because no one else ever has either. Or, rather, the usage regarding such punctuation is extravagantly subjective. It seems one of the only consistencies in the English language is that someone is always arguing over one point or another.
That said, I thought that Lynn Truss gave such a clarifying explanation of these two marks in Eats, Shoots & Leaves that I'd like to write about them here.
I've already written that you should use a semicolon when connecting a list separated by commas and you may use it to connect two related, complete clauses. Those are the technical rules.
A more nuanced idea explained Truss is that the semicolon should convey expectation:
"The semicolon tells you that there is still some question about the preceding full sentence; something needs to be added... The period tells you that that is that; if you didn't get all the meaning you wanted or expected, anyway you got all the writer intended to parcel out and now you have to move along. But with the semicolon there you get a pleasant feeling of expectancy; there is more to come; read on; it will get clearer. " pg 100
"The semicolon has been rightly called 'a compliment from the writer to the reader'. And a mighty compliment it is, too. The sub-text of a semicolon is, 'Now this is a hint. The elements of this sentence, although grammatically distinct, are actually elements of a single notion. I can make it plainer for you- but hey! You're a reader! I don't need to draw you a map!' By the same token, however, an over-reliance on semicolons- to give an air of authorial intention to half-formed ideas thrown together on the page- is rather more of a compliment than some of us care to receive." pg 108
I've really found my study of the semicolon very fascinating. I have learned that the use of the semicolon is really an art form and that punctuation can be nearly as important as word choice and syntax. I'm happy to have learned this. Yet, I know my limits. Punctuation may be an art form and, unfortunately, most of us aren't going to be Picasso. Actually, I don't even aspire to be that guy painting trees on PBS. But one day I would like to write a novel. It's on my "bucket list," you could say. I figure that at least knowing how to use a semicolon is a small step in the right direction. And if the novel doesn't work out, I'll at least be able to drive my children to become math majors with my ruthless editing of their papers.
Next week, the colon!