Lives and Opinions of Eminent Philosophers

​Now, the Canonic part contains introductions to the whole study, and is contained in the single work entitled The Canon. The Physical part contains the entire theory of nature, and is contained in the thirty-seven books On Nature and in the elementary letters. The Ethical part contains the matters concerning choice and avoidance; and it is contained in the books On Ways of Life, in the letters, and in On the Chief End. However, they are accustomed to group the Canonic together with the Physical; and they call the former "On the Criterion and First Principle" and "Elementary Exposition"; and the Physical "On Generation and Corruption" and "On Nature"; and the Ethical "On Things to Be Chosen and Avoided" and "On Ways of Life and the Chief End."

​Dialectic they reject as superfluous; for they say it is sufficient for natural philosophers to proceed according to the proper terms of things. Now, in The Canon Epicurus states that the criteria of truth are the sensations, the preconceptions (prolepseis), and the feelings; and the Epicureans add also the intuitive graspings of the intellect. He says this also in the Epitome to Herodotus and in the Principal Doctrines. "For every sensation," he says, "is irrational and incapable of receiving any memory; for neither being moved by itself nor by something else can it add or subtract anything; nor is there anything capable of refuting sensations.

​For neither can a homogeneous sensation refute a homogeneous one on account of their equal strength, nor an inhomogeneous one an inhomogeneous one, for they are not judges of the same objects; nor indeed can reason, for all reason is dependent upon the sensations; nor can one sensation refute another, for we attend to all of them. Moreover, the fact that perceptions subsist confirms the truth of the sensations. And our seeing and hearing subsist just as much as feeling pain; whence it is necessary to make inferences concerning unseen things from phenomena. For indeed all conceptions have arisen from sensations by coincidence, analogy, similarity, and combination, reasoning also contributing something. And the mental impressions of madmen and those in dreams are true, for they produce movement; and that which does not exist does not produce movement."

​By preconception (prolepsis) they mean a kind of comprehension, or correct opinion, or concept, or stored universal notion—that is, a memory of what has frequently appeared from without, such as: "A human being is of such a sort." For as soon as "human being" is uttered, immediately by preconception its outline is also conceived, the sensations having led the way. Therefore, with respect to every name, that which is primarily subordinated to it is self-evident; and we would not have sought what is being sought if we had not known it beforehand; as, for instance: "Is that which stands far off a horse or an ox?" For one must have known beforehand by preconception the form of a horse and an ox; nor would we have named anything if we had not previously learned its outline by preconception. Preconceptions, therefore, are self-evident; and that which is an object of opinion depends upon something self-evident that preceded it, referring back to which we say, for instance: "Whence do we know if this is a human being?"

​Opinion (doxa) they also call supposition (hypolepsis), and they say it is both true and false: for if it is attested to or not attested against, it is true; but if it is not attested to or is attested against, it turns out to be false. Whence the notion of "awaiting" was introduced; such as awaiting and getting near the tower and learning what sort of thing it appears when close up. They say feelings (pathe) are two, pleasure and pain, which subsist in every living being, the one being congenial, the other alien; through which choices and avoidances are judged. And of investigations, some concern things, while others concern mere words. Let this suffice, then, concerning the division and the criterion in an elementary way. We must now turn to the letter. "Epicurus to Herodotus, greetings.