Liz Clinch, who teaches at a comprehensive school in Devon, has asked for tips on explaining the use of colons and semi-colons. Here's our answer, in two parts: explanation and practice.
First then, explanation and understanding. One important point to be clear about is that the colon and semi-colon don't form a natural pair. Don't be misled by their similar shapes and names. It's true that they're linked historically: the colon came first and the semi-colon was derived from it.
But over time these two marks have developed different uses, so in our modern punctuation system they're quite different and it's usually not helpful to teach them together.
The colon has a clear meaning: amplification. What follows the colon amplifies what preceded it by adding details: (notice the colon!)
* I met three people: Tom, Dick and Harry.
* She's very clever: she speaks five languages.
Think of the colon as a pair of headlights: they point forward to what lies ahead. No other punctuation mark (apart from the infamous dash) has this meaning.
The semi-colon, on the other hand, has no particular meaning but lies halfway between a comma and a full stop. Think of it either as an overgrown comma (comma strengthened by a full stop) or an undergrown full stop (full stop weakened by a comma). What matters is the context: it's stronger than the surrounding commas, or weaker than the surrounding full stops. For example:
* Tom, Dick, Harry and Peter; and Mary (4 + 1)
* Tom; Dick, Harry and Peter; and Mary (1 + 3 + 1) Or:
* Jean was shouting. Mary was crying; that was really unusual. (1 + 2)
* Jean was shouting; Mary was crying. That was really unusual. (2 + 1)
How, then, to teach colons and semi-colons? First, teach them separately, rather than implying a special relation between them.
Second, explain the rules, and then let students explore written examples to see how the rules apply, case by case. Try changing the punctuation, to show that semi-colons can generally be replaced either by a comma or by a full stop, but colons can't be replaced.
Third, get students experimenting, comparing the effects of using different punctuation marks, looking at the abruptness created by full stops; the balance given by semi-colons. Get them thinking up their own definitions (like our "colons as headlights" example). Grammar is about learning through practice, not just through being taught rules. Colons and semi-colons give plenty of opportunity to put this principle into effect.
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