subject of Natural Philosophy; the second is one that he wrote to Pythocles, which is about the Heavenly Bodies; the third is addressed to Menœceus, and in that there are contained the discussions about lives.
We must now begin with the first, after having said a little by way of preface concerning the divisions of philosophy which he adopted.
XIX. Now he divides philosophy into three parts. The canonical, the physical, and the ethical. The canonical, which serves as an introduction to science, is contained in the single treatise which is called the Canon. The physical embraces the whole range of speculation on subjects of natural philosophy, and is contained in the thirty-seven books on nature, and in the letters again it is discussed in an elementary manner. The ethical contains the discussions on Choice and Avoidance; and is comprised in the books about lives, and in some of the Letters, and in the treatise on the Chief Good. Accordingly, most people are in the habit of combining the canonical division