I heard Paula Rabinowitz give a talk the other day involving an analysis of punctuation, and it reminded me of some of Nicholson Baker's work on the history of such punctuation marks as the semicolon and comma dash.
That's right, the comma dash: a combo-deal involving a comma and an em dash put together. Why don't most of us use the comma-dash? Or even know about it? Like the Carolina Parakeet, the comma dash went bye-bye.
[warning: bird-name segue] Eric Partridge and John Williams Clark have a nice book dealing with the topic in an unusual, mathematical way; see You Have a Point There: A Guide to Punctuation and its Allies. It's a GoogBook, so you can read it without much bother.
What's funky about what Partridge and Clark do is that they assign values to various punctuation marks in order to develop a value-based guide to usage. First, however, they contextualize some of the various ways punctuation marks can be combined:
So, as you can see, the comma-dash would rank between the comma and the semicolon. Of course, as a currently marked mark, that might throw off the ratings. Have you scored your punctuation marks today?
As Nicholson Baker points out, we tend to think of punctuation marks as static, unchanging, and absolute ... kind of like language. But punctuation marks and how they're used change. As CP reminded me this morning, I posted a little while ago about how folks here at the U of Ill are in the biz of inventing some pretty funky new marks.
So yeah,— go forth and punctuate.