  Some philosophers of language argue that sentences like “Cheating is morally wrong” are neither true nor false, because they resemble pure expressions of emotion (such as “Boo Knicks”) or prescriptions for action (such as “Go Celtics”). Such expressions and prescriptions are kinds of thing that cannot be either true or false. Thus, if these analogies hold in all relevant respects, then substantive moral beliefs are also not the right kind of thing to be either true or false. They are not apt for evaluation in terms of truth. For this reason, such linguistic theories are often taken to imply skepticism about moral truth-aptness. Views of this general sort are defended by Ayer (1952), Stevenson (1944), Hare (1981), Gibbard (1990; cf. 2003), and Blackburn (1993), although recent versions often allow some minimal kind of moral truth while denying that moral beliefs can be true or false in the same robust way as factual beliefs.