As we saw in the previous Chapter, in Popper's view, Kant's basic error was to assume that science was episteme, or that knowledge implies truth (Autob., 87; CR, 94), this assumption being, in turn, a consequence of Kant's alleged acceptance of the absolute authority of Newton's cosmology (CR, 26 etc.). Now, taking into consideration Kant's problem-situation as Popper reconstructed it, such an error was, in Popper's view, quite unavoidable and very little to be reproached (190). Yet, Popper goes on, it rendered Kant's problem insoluble (94). Without the assumption of the incontestable truth of Newtonian science, Popper maintains, Kant's problem "How is pure natural science possible?" collapses, and "the most disturbing of his perplexities disappears' (id.). Indeed, with hindsight, Popper came to think that his own critical rationalism and critical empiricism, precisely by revising that particular, erroneous assumption, put the finishing touch to Kant's critical philosophy (26/7). Kant, he says, "the great discoverer of the riddle of experience, was in error about one important point" (190, my italics). "But", he adds, "this error… was quite unavoidable, and detracts in no way from his magnificent achievement" (id.).