As someone who uses a fair amount of semi-colons (and almost always properly
) I think I a help with this a bit.
The reason you see so few of them in current works is because many writers (especially the published ones) have been taught/told to drop the complexity of their sentences, and indeed, their overall tone and style, to reach some magical lowest common denominator.
But, if you are writing more complex sentences, then you are most definately in need of some semi-colons.
Typically they are used to separate two independent clauses within the same sentence.
Put another way, sometimes you already have your subject and verb, but wish too expound upon them further. Lacking another subject/verb combo, you use a semi-colon to tack that expounding onto the sentence in progress.
If you use MS Word, it will often signfy the need for a semi-colon by marking a long sentence as a fragment, even though you can plainly see a subject and a proper predicate. Find the
write right spot to drop in that semi and voila, she is fixed.
The second reason to use them is for sentence rhythym (a bit longer of a pause than a comma), but at that point you have to watch your usage as you'll wind up using more than are called for, and in the wrong places.
Apparently, that's also what the "em dash" ( --) is for ...
I'm not sure I can recite any other rules for their use at this early hour.