 In the fourth chapter or Phenomenology of the Metaphysical Foundations Kant connects this reconstruction of Newton’s argument with the modal categories of possibility, actuality, and necessity—the very categories which (as we saw at the end of the second section above) make it possible for initially merely inductive generalizations (à la Hume) to acquire the status of necessary laws. The first stage, where we simply record the “phenomena” described by Kepler’s “rules” (as mere “appearances”:  note 36  above), corresponds to the category of possibility. The second stage, where we say that we here have instances of “true” (as opposed to merely “apparent”) rotation by appealing to the law of inertia, corresponds to the category of  actuality.[38]  In the third stage, finally, we apply the equality of action and reaction to the true centripetal accelerations correlated with such true rotations  (note 38  above); and all of them, in accordance with Kant’s metaphysical “dynamical theory of matter”, must now be taken as extending universally to infinity from each attracting point (compare notes  35  and  37  above). The result is the law of universal gravitation, now seen as falling under the category of necessity. In this way, Kant’s reconstruction of Newton’s “deduction” of the law of universal gravitation from the initial Keplerian “phenomena” provides a perfect illustration of the three-step procedure, described in the Postulates of Empirical Thought, by which a mere “empirical rule” is transformed into a “necessary and universally valid” objective  law.[39]