Let us grant that a linguist, qua theoretical and dispassionate scientist, is not in the business of telling people how to talk; it by no means follows that the speakers he is studying are free from rules which ought to be recorded in any faithful and accurate report of their practices. A student of law is not a legislator; but it would be a gross fallacy to argue that therefore there can be no right or wrong in legal matters.

Max Black, The Labyrinth of Language, New York, 1968, p. 70