The comma has so many jobs as a “separator” (punctuation marks are traditionally either “separators” or “terminators”) that it tears about on the hillside of the language, endlessly organising words into sensible groups and making them stay put: sorting and dividing; circling and herding; and of course darting off with a peremptory “woof” to round up any wayward subordinate clause that makes a futile bolt for semantic freedom. Commas, if you don’t whistle at them to calm down, are unstoppably enthusiastic at this job.
–Lynne Truss
[quotey goodness from Uncle Larry]