  The second conceptual challenge to the realist interpretation of validity is normative. The challenge is that there is an important sense in which diagnoses cannot be validated at all, if by “validation” we mean “shown to be a real disorder”. All validation can do is show that a pattern of behaviour deemed to be clinically significant depends on a physical process. Whether that pattern of behaviour is really pathological - rather than immoral or harmlessly odd- is another matter. The second challenge probably is very hard to meet. It requires that judgements of pathology be scientifically grounded, rather than human judgements. If so, there has to be some natural fact of the matter about whether some physical system is dysfunctional. If this cannot be done, then predictions about physical states can be validated, but disorders cannot be. 