Popper's theory o{ knowledge and Hare's analysis of the, language of values and morals are both widely (and correctly) regarded as philosophical breakthroughs. I want to show that a Popperian approach applies also, to value inquiry in a way which is consistent with Hare's prescriptivism.~ Scepticism about values arises from the same sort of mistakes that led to scepticism in epistemology. In value inquiry there has been the same mistaken search for a way of providing positive proof of knowledge claims. The search for a justifiable "is-ought" inference resembles the search for a justifiable inductive inference. But, o~ course, neither inference is logically possible. In both fMds there is the same mistaken search for an indubitable basis for knowledge. In ethics, this has taken a curious turn. The search has been for a descriptive basis for ethics, because the status of descriptive statements seems somehow on a stronger footing than that of value claims. But value claims can only be tested in terms of other value claims.
But I don't wish to dwell on the mistakes that led to, scepticism and Jrrationalism. Nor do I claim that I can fully justify a Po?perian approach to values, in this short paper. My primary claim here is that Popperian notions of testability, acceptability, corrigibility and the empirical basis apply in value inquiry. Furthermore, this does not commit one to naturalism in any way, and is fully consistent with Hare's prescriptivism.
Popper's main positive doctrines can be stated in five theses. Strictly speaking, (2) and ( 3) are not quite identical with Popper's published views, but are modifications propo,sed by Platt, Feyerabend, and the author. 2
(1) Factual and theoretical claims are to be tested in terms of other factual and theoretical claims.
(2) Testing is a matter of trying to decide between knowledge claims, by trying to refute the various alternatives. 1 1. W. N. Watkins has put forward a very similar thesis for mona! inquiry. See "Negative Utilitarianism,"