That’s what the usage and style guides frequently mentioned above are good for. There are bazillions of them. Nobody on any side is neglecting the issue. The point that descriptivists make is exactly that the process is not black and white and cannot be reduced to simple rules, hence guides instead of commands.
I always in these discussions bring up “good writing,” which is the writing normally seen in books and newspapers and magazines and suchlike. Almost all of the posts in these and similar threads will fall under the heading of “good writing.” It does communicate well, although not always perfectly.
However, there is no “standard” usage; rather that a variety of styles and personal choices go into “good writing.” Like any skill, it is something learned by practice and becomes better with experience. Great writers will expand the bounds of “good writing” sometimes in ways that are absorbable by others and sometimes in ways too idiosyncratic to be widely used. “Rules” do not aesthetically improve writing, although they may eliminate the flaws that impede communication or are looked down upon by a self-appointed superior class (see Pei above).
One of my favorite examples comes from the 1960s. As mentioned above, the descriptionist Webster’s Third Unabridged dictionary, the first thus, drove the prescriptionist crowd apeshit, mainly because it labeled certain words with neutral terms rather than “used only by low-grade illiterate morons.” (OK, an exaggeration. "[T]he dictionary did apply the labels slang, substandard and nonstandard, but in the view of critics, not often enough and with insufficient disapproval, and did away with the labels “improper” and “illiterate.”)
Other publishers saw an opportunity, in particular American Heritage. They also published American Heritage magazine, edited by Pulitzer Prize-winning historian Bruce Catton, and so tony that it came out in hardcover so people could save every issue on a bookshelf. The guy who ran the company, James Parton, hated what Webster’s did and after failing to buy their company to bury the thing decided to put out his own “proper” dictionary.
So that no one might doubt the authority of his labeling, he turned to a “usage panel” of about 100 well-known writers and academics and had them vote on whether some controversial usages were permissible, assuming there would be overwhelming unanimity on the answers.
There wasn’t. Instead, significant percentages, sometimes majorities, approved of every one. The dictionary sold well and was well-regarded, despite Parton’s meddling to dispute his own panel, but the notion that a single standard for good English existed was forever extinguished as a good argument for usage.
