perfection is an abstract, negative, metaphysical idea, or mode of considering objects, which supposes nothing real to be exterior to itself. _Twelfthly_, that matter is the principle of motion, which it contains within itself: since matter alone is capable of either giving or receiving motion: this is what cannot be conceived of immateriality or simple beings destitute of parts, devoid of extent, without mass, having no ponderosity, which consequently cannot either move itself or other bodies. CHAP. V. _Examination of the Proofs offered by DESCARTES, MALEBRANCHE, NEWTON, &c_. If the evidence of Clarke did not prove satisfactory--if the theologians of his day disputed the manner in which he handled his subject--if they were disposed to think he had not established his argument upon proper foundations, it did not seem probable that either the system of Descartes, the sublime reveries of Malebranche, or the more methodical mode adopted by Newton, were at all likely to meet with a better reception; the same objections will lie against them all, that they have not demonstrated the existence of their immaterial substances; although they have incessantly spoken of them, as if they were things of which they had the most intimate knowledge. Unfortunately this is a rock which the most sublime geniuses have not been competent to avoid: the most enlightened men have done little more than stammer upon a subject which they have all concurred in considering of the highest importance; which they unceasingly hold forth as the most necessary for man to know; without at the same time considering he is not in a condition to occupy himself with objects inaccessible to his senses--which his mind, consequently, can never grasp--which his utmost research cannot bring into that tangible shape by which alone he can be enabled to form a judgment.