34. Division of Philosophy. -- Philosophy, or science par excellence, is the investigation of the principles and causes of things (Metaph., I., i., 981); or again: it is the study of that which is necessary in things: in fact, there is no science except about the universal. Aristotle has indicated various ways of dividing philosophy. The best known is his classification of the philosophical sciences into theoretical, practical, and productive or poetic (poiein), according as the term or object of our knowledge is pure speculative information, or conduct (praxis), or the production (poiesis) of some exterior work.

Theoretical philosophy is subdivided so as to include

(1) Physics, or the study of corporeal things, subject to change (peri achôrista men all ouk akinêta).

(2) Mathematics, or the study of extension, that is, of a corporeal property not subject to change, and considered, by abstraction, apart from matter (p. akinêta men ou chôrista d isôs, all hôs en hulê).

(3) Metaphysics, called Theology or First Philosophy, or the study of being in its incorporeal (by abstraction or by nature) and immovable (p. chôrista kai akinêta) states or conditions.

Practical Philosophy includes ethics, economics, and politics, the second often going with the third.

It is difficult to insert the treatises of the Stagirite himself in this classification, on account of the disordered condition in which many of them have come down to us. Besides, it leaves no room for Logic, the vestibule of philosophy, and the object of Aristotle's deepest study. We will follow the division as outlined, adding logic as a preliminary, and we will examine successively: (1) Logic; (2) Theoretical philosophy: (a) Metaphysics; and Theodicy, its complement; (b) Mathematics; (c) Physics, general and special; (3) Practical philosophy: (a) Ethics; (b) Politics; (4) Poetics.