I've just learned about The ESL Help! Desk. It's a good website if you're learning English as a second or foreign language. In addition to advice about grammar, it offers a very readable blog. I'm putting it in the ESL/EFL Resources links.
I would like to hypothesize that a new form of colon has emerged. From the democratic bowels of the Internet, an unknown pair of beady black eyes is staring out at us.
It’s colon number 5.
At The New York Times, Roger Cohen certainly uses it. “Not history but the future: Germany, when I lived there in the late 1990s….” Or here, when he writes, “On Turkey, for example: Barack tells me Turkey is Europe’s Islamic bridge.”
Also a fan is Paul Krugman. “Some background: we used to have a workable system for avoiding financial crises….” Or again, adding, “And one more thing: employment-based health insurance….”
A new colon is on the march. For now let’s call it the “jumper colon”.
Actually, all five colons do the same basic thing: They prepare you for an explanation or illustration of what you've just read.
You can't use a colon, by the way, to introduce a list that's grammatically part of the sentence. If your sweetie sent you an email saying, "I love: you," you would be touched but also surprised at her bad education. If she wrote, "I love: you, Bill, Tom, John, and Derek," she would still be ungrammatical as well as unfaithful.
But if she wrote: "I love many men: you, Bill, Tom, John, and Derek," at least you couldn't complain about her bad punctuation. A colon introduces a list, all right, but it's a list that is grammatically separate from the sentence.
The semicolon, by contrast, tells you that you've read a complete sentence and another complete sentence is on its way; it is so related in meaning to the first that you keep reading. The main exception is when we use a semicolon in lists that contain internal commas. For example:
Visitors have come from Seattle, Washington; Memphis, Tennessee; Toronto, Ontario; and Horsefly, British Columbia.
We need the semicolons to set off each of the terms. And notice that we don't start the list with a colon because the terms are grammatically part of the sentence.
While the colon is clearly finding lots of uses, the dash—believe it or not—remains the duct tape of punctuation. You can use it instead of a colon, a semicolon, or parentheses. But like duct tape, using too much of it creates a slapdash look to your writing.