For the personal appearance of Socrates, read Plato, _Symposium_, pp. 586 ff. and Xenophon, _Symposium_, p. 615. For the physical endurance of Socrates, read Plato, _Symposium_, p. 591. For Socrates’ dislike of nature, read Plato, _Phædrus_, p. 435, and Xenophon, _Memorabilia_, p. 521. For the charges, defense, and trial of Socrates, read Plato, _Apology_, pp. 116 and 129. For the confinement of Socrates in prison, read _Crito_, beginning and end of the dialogue. For description of the death scene of Socrates, read Plato, _Phædo_, beginning and end of the dialogue. For description of the dæmoniacal sign, read Plato, _Apology_, pp. 125–126, and Xenophon, _Memorabilia_, pp. 531 ff., 585 ff. For the oracle’s statement that Socrates is the wisest of men, read Plato, _Apology_, p. 114. 18 – What is the difference between perception and conception? We have heard a good deal about perceptions in the doctrine of Protagoras. We have now reached a point where many of the theories will involve a comparison of perception with conception. An understanding of the difference between perception and conception will be necessary for an understanding of the doctrines, especially of Democritus, Plato, and Aristotle. In general, perception is the consciousness of an object in which some actual sensation of it is present; a conception is the consciousness of an object in which no actual sensation of it is present. Thus I perceive a tree, when my retina is actually stimulated; I conceive a tree, when I turn my head away and no sense organ is actually stimulated, _i. e._ I do not touch, see, hear the tree. To the Greek the perception was particular and transient; the conception was, on the other hand, universal or general and permanent. 19 – Read Zeller, _Pre-Socratic Phil._, vol. i, pp. 138–149, concerning the objective character of Greek morality, art, and philosophy. 20 – Zeller, _Pre-Socratic Phil._, vol. i, p. 162. 21 – Zeller, _Pre-Socratic Phil._, vol. i, p. 162. 22 – Rationalism and sensationalism refer to the sources from which knowledge is obtained. Rationalism is to be contrasted with sensationalism. Rationalism is the belief that the reason is an independent source of knowledge and has a higher authority than sense-perception. Sensationalism is the belief that all our knowledge originates in sensations. Empiricism is often used for sensationalism.