 For Kant, therefore, the laws of the Newtonian science of nature are of two essentially different kinds. Kant regards Newton’s three “Axioms or Laws of Motion” presented at the beginning of the Principia as synthetic a priori truths—which Kant himself attempts to demonstrate a priori in the Metaphysical  Foundations.[12]  By contrast, Kant does not regard the inverse-square law of universal gravitation, which Newton establishes by a famous “deduction from the phenomena” in Book 3 of the Principia, as a synthetic a priori truth—and, accordingly, Kant does not attempt to demonstrate this law a priori in the Metaphysical Foundations. Nevertheless, Kant regards the synthetic a posteriori law of universal gravitation as “necessary and universally valid” in virtue of the way in which it is “determined” in relation to the “phenomena” by the synthetic a priori laws of pure natural science. And, since the latter, in turn, are “determined” from the a priori principles of the understanding, the a posteriori law of universal gravitation is thereby “determined” in relation to actual perceptions “in accordance with the general conditions of  experience”.[13]