LXV. Perhaps some one will remark to me, that the substantial nature of things is at a great distance from our view, and that therefore it is not wonderful, that we have not yet penetrated into the inmost recesses of philosophy; for that without advancing so far, we may find sufficient matter whereon to exercise our speculations, in contemplating the ordinary phenomena of nature, and by endeavouring to discover their proximate causes; which attempt, may possibly be crowned with success, by observing and reasoning upon every species of movement which is performed by an entity, that has motion or circulation, according to the nature of such an entity. LXVI. I will acknowledge, that philosophy helps us to reason upon natural phenomena, and to enquire into their more immediate causes; but in doing this, we frequently wander in the dark, and are much exposed to be interrupted by impediments, produced by ignorance and doubts; except it is in the case of a few truths, the discovery of which, we owe to the light of experience; and this fact is evinced, with respect to the very instance of motion which has been just alledged. LXVII. With regard to the movements of generation, corruption, alteration, augmentation, and the rest, which are considered as distinct from local motion, you can find nothing that is not questionable, both in the schools of the Aristotelites, and in those of the modern philosophers. The very definition of motion in general, which was given by Aristotle, some reject as obscure, others as perplexed, and others as nugatory. The movements we are now treating of, in the opinion of Aristotle, are acquisitions of new forms, either substantial, or accidental; but the Moderns, who deny the existence of all material forms, object to this definition of those movements. Even among the Aristotelites themselves, it is not agreed, whether motion is not influenced by passion; nor whether the first, is not obedient as a passive agent to the last. And thus in every thing else, it is all question, and all dispute. SECT. XVII. LXVIII. And why should we be surprized that with respect to these movements, which as we may say, nature executes behind the curtain, human understanding has made so little, or next to no advances? what we ought more to wonder at, is, that it happens the same with respect to all local motion, which lies so plain and open to our observation.