That is to say, the proofs are a posteriori, resting on experience. The order of nature is an historical order, particularly in its coexistences. It may be objected that the physicist may prescind entirely from the question agitated in this chapter. So indeed he may. But St Thomas's 'natural science' includes physics and metaphysics. Metaphysics rest on an a posteriori basis of sensory experience. The enquiries in Aristotle's eight books of Physics are chiefly metaphysical. No doubt, physics have gained by being made a speciality, apart from metaphysics. The former is the lower, the latter the higher science. You may stop short of the higher: but you can be no great master of the higher if you are quite a novice in the lower. Nemo metaphysicus quin idem physicus.

Of God and His Creatures: 3.69