Kant's comment of 1787 on the astronomical or "Copernican " revolution has raised very controversial issues, which are strictly interrelated with his approach to Newtonian science. Both topics need to be revisited in the light of recent scholarship. This paper focuses on Kant's non-technical grasp of the so-called "Newtonian method", a powerful tool that he pretended to borrow for promoting new enquiry into the old "battlefield of metaphysics". By the end of his pre-critical trials and errors, he claimed to have re-established the leadership of the "scientia prima", now called trascendental philosophy, and put the definitive foundations of a "pure" science of nature. From his new critical vantage-point, he assigned an "a priori" epistemological sanction even to Newton's law of universal gravitation. In this way the most brilliant outcome of Newton's "mathematical way" and experimental science was transformed into an absolute principle stemming from pure reason. This seems to be - historically reconsidered - a circular argument, which represents a serious challenge for some recent attempts to modernize Kant's late speculations about the gap separating the a priori from the "a posteriori", the "pure" from the "empirical" "Natur-wissenschaft".