William Gass on Kinds of Commas

From “Enter a Sentence of Elizabeth Bishop’s: Revision and Craft," a new review-essay by William H. Gass in the October 2011 Harper’s:

As if in the shade of Emily Dickinson (at first not a favorite), Elizabeth Bishop was inclined to scatter dashes about (a habit perhaps borrowed from her letters, or in hidden imitation of a mentor, Marianne Moore), which these New Yorker editors removed and replaced with commas, also, it seems, in similar abundance. Alas, there are so many kinds of commas: those that lie like rocks in the path of a sentence, slowing its gait and requiring the reader’s heed to avoid a stumble; their gentler cousins, impairing a pell-mell flow of meaning the way pebbles slow a stream; commas that indicate a pause for thinking things over; commas enclosing phrases the way the small pockets in a purse hug hairpins or collect bits of loose change; commas that return us to our last stop, and those that some schoolmarm has insisted should be placed, like a traffic cop, between "stop” and “and.” Not to mention those comma-like curvatures that function like overhead lighting — apostrophes they’re called — that warn of a bad crack in a spelt word where some letters have disappeared to apparently no one’s alarm; or claws that admit the words they enclose aren’t theirs; or those that issue claims of ownership, called possessives by unmarried teachers.