[Sidenote: Parts of philosophy.] =143.= The history of Greek philosophy, even before the time of Zeno, leads naturally to its division into the three parts of logic, physics, and ethics[1]. The Ionic philosophers had chiefly occupied themselves with the nature and history of the universe, that is, with the problems of physics. The sophists were greatly concerned with questions as to the validity of human knowledge, that is, with logic. Socrates shared this interest, but attached greater importance to the discussion of moral activities, that is, to ethics. It is however not clear when a formal division into these three parts was first made. Cicero attributes it to the immediate followers of Plato in the Academic school; others assign it definitely to Xenocrates[2]. The Peripatetics and Stoics both adopted the division, but whereas the former assigned to Logic an inferior position, making it an introduction to philosophy, the Stoics insist that it is a part of philosophy itself[3]; and that of the three parts it comes first in the order of study, ‘as in the measuring of corn we place first the examination of the measure[4].’ It must not however be thought that the three parts of philosophy can be separately treated, for they are intertwined[5]; so that in treating of Logic we shall constantly have need to assume a general knowledge of Stoic views both on physics and ethics. Logic is subdivided into ‘dialectic,’ which deals with reasoning, and ‘rhetoric,’ the art of speech. The relation between reason and speech was in ancient times, as now, a matter of perplexity; but it may be taken as a fundamental position of Stoicism that the two should always be in agreement. [Sidenote: Knowledge is attainable.] =144.= Stoicism, as one of the positive and dogmatic schools, assumes that knowledge is attainable. Since this is the very point on which Socrates never reached assurance, except on the one particular that he himself knew nothing, it was a matter of primary importance to the Stoics to make good this position; more especially since they held (this time in agreement with Socrates) that virtue is but another form of knowledge. Yet the Stoics could not agree with the Cynics, that true knowledge can be imparted without a study of its method[6]. Knowledge is, in their view, a high privilege derived by man from his divine ancestry, and shared by him with the deity alone; and the whole duty of man may be summed up by saying that he should keep upright his reason[7]. They therefore devoted themselves with special zeal to this part of philosophy[8], and were accordingly nicknamed ‘the dialecticians[9].’ Their aim in this was solely the ascertainment and imparting of truth; but the common view that their style was in consequence harsh and repellent will be found to need considerable qualification[10]. [Sidenote: Are the senses true?]