Epicurus himself produced in his lifetime an immense number of works, being a much more prolific author than Chrysippus, who vied with him in the number of his writings,[147] if we deduct from the latter his compilations from the works of others or from his own. The number of his writings is said to have amounted to three hundred; it is scarcely to be regretted that they are lost to us. We may rather thank Heaven that they no longer exist; philologists at any rate would have had great trouble with them. The main source of our knowledge of Epicurus is the whole of the tenth book of Diogenes Laërtius, which after all gives us but scanty information, though it deals with the subject at great length. We should, of course, have been better off had we possessed the philosopher’s own writings, but we know enough of him to make us honour the whole. For, besides this, we know a good deal about the philosophy of Epicurus through Cicero, Sextus Empiricus and Seneca; and so accurate are the accounts they give of him, that the fragment of one of Epicurus’s own writings, found some years ago in Herculaneum, and reprinted by Orelli from the Neapolitan edition (Epicuri Fragmenta libri II. et XI. De natura, illustr. Orellius, Lipsiæ 1818), has neither extended nor enriched our knowledge; so that we must in all earnestness deprecate the finding of the remaining writings. With regard to the Epicurean philosophy, it is by no means to be looked on as setting forth a system of Notions, but, on the contrary, as a system of ordinary conceptions or even of sensuous existence, which, looked at from the ordinary point of view as perceived by the senses, Epicurus has made the very foundation and standard of truth (p. 277). A detailed explanation of how sensation can be such, he has given in his so-called Canonic. As in the case of the Stoics, we have first to speak of the manner which Epicurus adopted of determining the criterion of truth; secondly, of his philosophy of nature; and thirdly and lastly, of his moral teaching. 1. CANONICAL PHILOSOPHY. Epicurus gave the name of Canonic to what is really a system of logic, in which he defines the criteria of truth, in regard to the theoretic, as in fact sensuous perceptions, and, further, as conceptions or anticipations (προλήψεις); in regard to the practical, as the passions, impulses, and affections.[148] a. On the theoretic side the criterion, closely considered, has, according to Epicurus, three moments, which are the three stages of knowledge; first, sensuous perception, as the side of the external; secondly, ordinary conception, as the side of the internal; thirdly, opinion (δόξα), as the union of the two.