9. Likewise some of the teachers have defined philosophy in its name and parts as follows: “Philosophy is the probable knowledge of divine and human affairs, as far as is possible for man.” Otherwise: “Philosophy is the art of arts and the science of sciences.” Again: “Philosophy is the meditation upon death, a definition which better suits the Christians, who trampling on worldly ambition, live in the intercourse of learning after the likeness of their future country.”
10. Others have defined the scheme of philosophy as made up of two parts, of which the former is contemplative, the latter practical. The contemplative (inspectiva) is divided into natural, theoretical, and divine. Theoretical is divided into four parts, into arithmetic, music, geometry, and astronomy.
11. Practical (actualis) philosophy is divided into moral, economic, and civil. Contemplative is the name given that in which, passing beyond the visible, we enjoy some contemplation of the divine and celestial, and behold them with the mind alone, since they pass beyond the bodily gaze.
12. Natural philosophy is the name given when the nature of each and every thing is discussed, since nothing arises contrary to nature in life, but each thing is assigned to those uses for which it was purposed by the Creator, unless perchance by God’s will it is shown that some miracle appears.
13. It is called divine philosophy when we discuss the ineffable nature of God or the spiritual beings that are in some degree of a lofty nature.
14. The science which considers abstract quantity is called theoretical. For that is called abstract quantity which we separate from the material, or from other accidents, by the intellect, and treat by reasoning alone, as e.g., equal, unequal, and other matters of this kind....
16. Further, that is called practical philosophy which by its workings makes problems clear, of which there are three parts, moral, economic, and civil. That is called moral by which an honorable custom (mos) of living is sought and practices tending to virtue are established. That is called economic (dispensativa) in which the order of domestic affairs is wisely arranged. That is called civil by which the advantage of a whole state is secured.
Chapter 25. On the Isagoges of Porphyry.
1. After the definitions of philosophy in which all things are embraced under general heads, let us now describe the Isagoges of Porphyry. Isagoge in the Greek means introductio in the Latin, being meant for those, it is plain, who are beginning philosophy, and containing an explanation of first principles. In regard to anything whatever it is made clear what its nature is, by unfailing definition of the substance.
2. For setting down first the genus, then the species, we subjoin also other things that are possibly related, and by setting aside common qualities we make distinctions, continually interposing differences until we arrive at the proper quality of that which we are examining, its meaning being made definite, as, for example: Homo est animal rationale, mortale, terrenum, bipes, risus capax.