The second principle made use of by Plato, and by most of the speculative philosophers, is a final cause. Nevertheless, to reduce this principle to its just value, a single moment of reflection is only requisite. To say there is light because we have eyes, and sounds because we have ears, or to say that we have ears and eyes because there is light and sound, is it not exactly the same thing? shall we ever discover any thing by this mode of explanation? Is it not evident that final causes are only arbitrary relations and moral abstractions, which should impose on us still less than metaphysical abstractions, because their origin is less noble and a more false supposition; and although Leibnitz has endeavoured to raise this principle to the highest degree by the name of _sufficient reason_, and Plato has represented it by the most flattering portrait, under the title of _perfection_, yet it cannot prevent our seeing it as trifling and precarious. Are we better acquainted with the effects of Nature, from being told that nothing is made without a reason, or that all is made in view of perfection? What is this sufficient reason? what is this perfection? are they not moral beings created by intellects purely human? are they not arbitrary relations which we have generalized? on what are they founded? on moral affinities which, far from producing any physical or real existence, only alter the reality and confound the objects of our sensations, perceptions and knowledge, with those of our sentiments, our passions and our wills. I could adduce many arguments on this subject, but I do not pretend to make a treatise on philosophy, and shall return to physics, from which the ideas of Plato on universal generation made me digress. Aristotle, who was as great a philosopher as Plato and a much better physician, instead of losing himself in the region of hypotheses, relied, on the contrary, on collected facts, and speaks in a more intelligible language.