The Peripatetic philosophy asserts the _original_ matter to be perfectly homogeneous in all bodies, and considers fire, water, earth, and air, as of the very same substance, on account of their gradual revolutions and changes into each other. At the same time it assigns to each of these species of objects a distinct _substantial form_, which it supposes to be the source of all those different qualities they possess, and to be a new foundation of simplicity and identity to each particular species. All depends on our manner of viewing the objects. When we look along the insensible changes of bodies, we suppose all of them to be of the same substance or essence. When we consider their sensible differences, we attribute to each of them a substantial and essential difference. And in order to indulge ourselves in both these ways of considering our objects, we suppose all bodies to have at once a substance and a substantial form. The notion of _accidents_ is an unavoidable consequence of this method of thinking with regard to substances and substantial forms; nor can we forbear looking upon colours, sounds, tastes, figures, and other properties of bodies, as existences, which cannot subsist apart, but require a subject of inhesion to sustain and support them. For having never discovered any of these sensible qualities, where, for the reasons above mentioned, we did not likewise fancy a substance to exist; the same habit, which makes us infer a connexion betwixt cause and effect, makes us here infer a dependence of every quality on the unknown substance. The custom of imagining a dependence has the same effect as the custom of observing it would have. This conceit, however, is no more reasonable than any of the foregoing. Every quality being a distinct thing from another, may be conceived to exist apart, and may exist apart not only from every other quality, but from that unintelligible chimera of a substance. But these philosophers carry their fictions still farther in their sentiments concerning _occult qualities_, and both suppose a substance supporting, which they do not understand, and an accident supported, of which they have as imperfect an idea. The whole system, therefore, is entirely incomprehensible, and yet is derived from principles as natural as any of these above explained.