 Kant's 1781 book introduced the distinction "rationalism", whereby some knowledge results not by "empiricism", but instead by "pure reason".Concluding it impossible to know reality in itself, however, Kant discarded the philosopher's task of unveiling appearance to view the "noumena", and limited science to organizing the "phenomena".Reasoning that the mind contains categories organizing sense data into the experiences "substance", "space", and "time", Kant thereby inferred uniformity of nature, after all, in the form of "a priori" knowledge.