Essentially, descriptivists and prescriptivists are approaching different problems. Descriptivists want to record language as it's actually used, and they perform a useful function—though their audience is generally limited to those willing to pore through vast tomes of dry-as-dust research. Prescriptivists—not all of them, perhaps, but enlightened ones—want to figure out the most effective uses of language, both grammatically and rhetorically. Their editorial advice should accord with the predominant practices of the best writers and editors.
