The possibility of a genuine metatheory of morality is not available. Even psychology has its ethical presuppositions. ... A metatheory of morality would be legitimate only if the existence of a hierarchy of absolute, and hence unconditioned, truths were established. They would then provide a framework of supra-ethical categories. The primary ambition of Nietzsche's critique of knowledge is to expose just such an exercise ... as sleight of hand, an efficacious deception. This critique sets out to demonstrate that ‘truths' are fictions masking moral commitments.