Similar things may be said about the explanation of natural philosophy, which both the Peripatetics and Stoics apply themselves to; and that not on two accounts only, as Epicurus thinks, namely, to get rid of the fears of death and of religion; but besides this, the knowledge of heavenly things imparts some degree of modesty to those who see what great moderation and what admirable order there is likewise among the gods: it inspires them also with magnanimity when they contemplate the arts and works of the gods; and justice, too, when they come to know how great is the power and wisdom, and what the will is also, of the supreme ruler and master of the world, whose reason, in accordance with nature, is called by philosophers the true and supreme law. There is in the same study of nature, an insatiable kind ofpleasure derived from the knowledge of things; the only pleasure in which, when all our necessary actions are performed, and when we are free from business, we can live honourably, and as becomes free men. Therefore, in the whole of this ratiocination on subjects of the very highest importance, the Stoics have for the most part followed the Peripatetics; so far at all events as to admit that there are gods, and to assert that everything consists of one of four elements. But when an exceedingly difficult question was proposed, namely, whether there did not seem to be a sort of fifth nature from which reason and intelligence sprang; (in which question another was involved respecting the mind, as to what class that belonged to;) Zeno said that it was fire; and then he said a few more things—very few, in a novel manner; but concerning the most important point of all, he spoke in the same way, asserting that the universal world, and all its most important parts, were regulated by the divine intellect and nature of the gods. But as for the matter and richness of facts, we shall find the Stoics very poorly off, but the Peripatetics very rich.
What numbers of facts have been investigated and accumulated by them with respect to the genus, and birth, and limbs, and age of all kinds of animals! and in like manner with respect to those things which are produced out of the earth! How many causes have they developed, and in what numerous cases, why everything is done, and what numerous demonstrations have they laid open how everything is done!And from this copiousness of theirs most abundant and undeniable arguments are derived for the explanation of the nature of everything. Therefore, as far as I understand, there is no necessity at all for any change of name. For it does not follow that, though he may have differed from the Peripatetics in some points, he did not arise out of them. And I, indeed, consider Epicurus, as far as his natural philosophy is concerned, as only another Democritus: he alters very few of his doctrines; and I should think him so even if he had changed more: but in numerous instances, and certainly on all the most important points, he coincides with him exactly. And though the men of your school do this, they do not show sufficient gratitude to the original discoverers.