 The synthetic statements of the empirical sciences meanwhile were held to be cognitively meaningful if and only if they were empirically testable in some sense. They derived their justification as knowledge claims from successful tests. Here the Circle appealed to a criterion of meaningfulness (cognitive significance) the correct formulation of which was problematical and much debated (and will be discussed in greater detail in section 3.1 below). Roughly, if synthetic statements failed testability in principle they were considered to be cognitively meaningless and to give rise only to pseudo-problems. No third category of significance besides that of a priori analytical and a posteriori synthetic statements was admitted: in particular, Kant’s synthetic a priori was banned as having been refuted by the progress of science itself. (The theory of relativity showed what had been held to be an example of the synthetic a priori, namely Euclidean geometry, to be false as the geometry of physical space.) Thus the Circle rejected the knowledge claims of metaphysics as being neither analytic and a priori nor empirical and synthetic. (On related but different grounds, they also rejected the knowledge claims of normative ethics: whereas conditional norms could be grounded in means-ends relations, unconditional norms remained unprovable in empirical terms and so depended crucially on the disputed substantive a priori intuition.)