Philosophy was defined by the Stoics as 'the knowledge of things divine and human'. It was divided into three departments; logic, ethic, and physic. Of the three departments we may say that logic deals with the form and expression of knowledge, physic with the matter of knowledge, and ethic with the use of knowledge. The division may also be justified in this way. Philosophy must study either nature (including the divine nature) or man; and, if it studies man, it must regard him either from the side of the intellect or of the feelings, that is either as a thinking (logic) or as an acting (ethic) being. Coming with a new large print edition, this guide is followed by the biographies of various Stoic philosophers taken from "The lives and opinions of eminent philosophers" by Diogenes Laërtius.