Our weather (in Fort Worth) is perfect for running: 45º and sunny, with a gentle southerly breeze. (We're coming out of a cold spell.) During my 3.1-mile run just now, I came upon three young men. One of them asked, "Do you be runnin' marathons?" I was tempted to say, "Yes, I do be runnin' marathons," but he might have taken offense, so I said, "Yes, I do." (Technically, I no longer run marathons, though I've completed 11 of them; there wasn't time to explain.)
This incident got me to thinking, during the remainder of the run, about the distinction between descriptivism and prescriptivism as regards usage. Descriptivists say that usage is neither correct nor incorrect, but only more or less effective. Since I understood what the young man said, an effective act of communication occurred. It adds nothing to say that his speech was "incorrect." Most linguists are descriptivists, since linguistics is a social science and science, as such, is about describing the world (i.e., getting it right) rather than prescribing how the world ought to be (i.e., setting it right).
The prescriptivist, by contrast, says that usage is either correct or incorrect. In this case, it was incorrect, however effective it may have been. What say you? Are you a prescriptivist? If so, would you have corrected the young man, since he was speaking nonstandard English? Would have you said, for example, "Look, I understand your question, but you really ought to use proper grammar"?
Keith Burgess-Jackson, J.D., Ph.D. 