Relativism about science is also influenced by the related doctrine that all observations are theory-laden. Even anti-relativists such as Karl Popper admit that the idea that observations are not in some way tinted by theoretical assumptions is naïve. But some relativists about science offer a particularly extreme form of the doctrine of the widely accepted thesis of theory-ladenness. Feyerabend, for instance, goes so far as to argue that different systems of classification can result in perceptual objects that are not easily comparable.