The Grammar Girl has something to say about dashes, commas and colons.
“People sometimes ask me about the difference between a colon and a dash since they can both be used to introduce the next part of a sentence,” Mignon Fogarty writes. She goes on to give a thorough and fairly understandable explanation of their differences and when to use them.
For grammar geeks like us, this is heady stuff. Finally, we’ve found a simple justification for our style choices that – to the uneducated – can appear arbitrary, even nonsensical.
Admittedly, the difference between a dash and colon can be, well, subtle. She does a nice job explaining it all. As a bonus she gives a good rundown of when to use commas instead of dashes or colons, and how to integrate them all when using quotation marks.
She is seriously into her punctuation. I think we might have to be friends.
Not everyone takes punctuation this seriously. But you’ll be amazed at how much more fluent and persuasive your own writing can be when you play by the rules.