Note 38 — Chapter XIV · THE STOIC PHILOSOPHY AS A WHOLE AND ITS HISTORICAL POSITION.

(3) Opinion. For this very reason notion are not sufficient. From appearances we must advance to their secret causes; from the known to the unknown.38 Far too little value was attached by Epicurus to the logical forms of thought, or he would have investigated more accurately the nature of this process of advancing.39 Thoughts, in his view, result from sensations spontaneously, and although a certain amount of reflection is necessary for the process, yet it requires no scientific guidance.40 The thoughts arrived at in this way do not stand as a higher genus above perceptions, but they are only opinions (ὑπόληψις, δόξα) without a note of truth in themselves, and depending for their truth upon sensation. That opinion may be considered a true one which is based on the testimony of the senses, or is at least not contrary to the senses, and that a false opinion in which the opposite is the case.41 Sometimes we suppose that upon certain present impressions other impressions will follow: for instance, that a tower which appears round at a distance will appear round close at hand. In that case, if the real perception corresponds with the assumption, the opinion is true, otherwise it is false.42 At other times we suppose that certain appearances are due to secret causes: for instance, that empty space is the cause of motion. If all appearances tally with their explanations, we may consider our assumptions correct; if not, our assumptions are incorrect.43 In the first case the test of the truth of an opinion is that it is supported by experience; in the latter that it is not refuted by experience.44 Have we not here all the leading features of a theory of knowledge based purely on sensation? The Epicurean’s interest in these questions was, however, far too slight to construct with them a developed theory of materialism.