 The most important figure in German-speaking Europe to react in depth to Newton’s ideas was surely Immanuel Kant. As a young man, Kant was influenced by Euler’s argument (Friedman 1992: 16–17) in the 1748  piece.[26]  Kant began grappling with Newtonian ideas at the very beginning of his career—he discussed the inverse-square law in his first publication (Kant 1747: § 10)—and they would remain central both to his magnum opus, the Critique of Pure Reason (Kant 1787 [1992]) and to his Metaphysical Foundations of Natural Science (1786 [2002]). In the so-called pre-critical period, Kant diverged sharply from the approach toward natural philosophy defended by many Leibnizians in German-speaking Europe by deciding to accept the Newtonian theory of universal gravity, along with corresponding aspects of the Newtonian conception of matter, as a starting point for philosophical theorizing (Friedman 2012: 485–6). He makes this explicit already in 1763, in The Only Possible Argument: