The synthetic a priori laws of pure natural science are themselves 'determined' from the a priori principles of the understanding

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 Principi