Philosophy was defined by the Stoics as 'the knowledge of things divine and human'. It was divided into three departments; logic, ethic, and physic. This division indeed was in existence before their time, but they have got the credit of it as of some other things which they did not originate. Neither was it confined to them, but was part of the common stock of thought. Even the Epicureans, who are said to have rejected logic can hardly be counted as dissentients from this threefold division. For what they did was to substitute for the Stoic logic a logic of their own, dealing with the notions derived from sense, much in the same way as Bacon substituted his Novum Organum for the Organon of Aristotle. Cleanthes we are told recognised six parts of philosophy, namely, dialectic, rhetoric, ethic, politic, physic, and theology, but these are obviously the result of subdivision of the primary ones. 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. As to the order in which the different departments should be studied, we have had preserved to us the actual words of Chrysippus in his fourth book on Lives. 'First of all then it seems to me that, as has been rightly said by the ancients, there are three heads under which the speculations of the philosopher fall, logic, ethic, physic; next, that of these the logical should come first, the ethical second, and the physical third, and that of the physical the treatment of the gods should come last, whence also they have given the name of "completions" to the instruction delivered on this subject'. That this order however might yield to convenience is plain from another book on the use of reason, where he says that 'the student who takes up logic first need not entirely abstain from the other branches of philosophy, but should study them also as occasion offers.'