Cursus Philosophicus Thomisticus, Prima Pars Philosophiae Naturalis

Philosophy, if it is taken in the whole breadth of its signification, encompasses all science; for philosophy is said to be, as it were, the "love of science" or "friendship of science," by which account human wisdom is called philosophy by St. Thomas in the preface of the Ethics. And thus philosophy is a generic science encompassing under itself every naturally acquirable science, especially the speculative, the love of which is properly the love of science, because it is loved only for the sake of knowing.

A threefold genus of this speculative science is enumerated by the Philosopher¹ and St. Thomas in Metaphysics XI, lect. 7 and Opusculum 70, q. 5:² namely, natural science, mathematics, and metaphysics. Logic is also placed reductively under it, which deals not with things to be speculated upon, but with the very instruments of speculation. These sciences differ according to a diverse degree of knowability, as we have said in the books of the Posterior Analytics, q. 27.³ For natural science treats of things subject to motion and sensible change, and therefore it abstracts only from singular matter. Mathematics deals with quantity, insofar as it abstracts from motion and from matter clothed with sensible accidents. Metaphysics deals with being as such, insofar as it abstracts from all matter, both sensible and intelligible—that is, even from prime matter according to itself, which is perceived by the intellect alone.

Philosophy taken in this breadth is defined variously by authors. For some define philosophy from the etymology of the name, which is the "love of wisdom"; others from the mode of proceeding, which is the "knowledge of things as they are," that is, through their causes. Others, who define philosophy from the matter which it embraces, say that it is the "knowledge of human and divine things." Lastly others, who define philosophy from the effect to which it leads us, have said that it is the "contemplation of death," i.e., separating man from temporal and corporeal passions.

At present, we do not treat of philosophy in its total breadth. Rather, having left aside mathematics and metaphysics, we treat only of natural science, whose object comprehends every natural being, i.e., every mobile being according to some corporeal or extended motion, for purely spiritual motions do not pertain to this genus of science.

In considering this object, Aristotle proceeded in the highest order, dividing this science into four parts:

The first deals with mobile being in common, for one proceeds scientifically from the more common to the less common. And this part is concluded in the eight books which they call the Physics or the "Lectures on Nature."

The remaining three parts deal with mobile being in particular. And according to the three species of motion, they are distinguished into three genera of mobile things, as St. Thomas observes in the preface of the books On Generation. The first is local motion; the second, alteration, which is ordered toward generation; the third, augmentation, which is proper to a living or animated thing. And according to the first motion, simple bodies are considered, from which this universe is constructed. And thus after the books of the Physics, the Philosopher treats of the heavens and the world,⁴ that is, of all simple bodies, insofar as they are coordinated and situated in this universe through local motion. For from these the universe especially consists; for mixed things have their place according to the mode of the element predominating in them. According to the motion of alteration, however, which is ordered toward generation, he treats of corruptible bodies, not insofar as they are coordinated by position in the universe, but insofar as they are subject to generation and corruption, both substantial and accidental. Thus the third part of philosophy deals with generation.⁵ Finally, according to the third genus of motion, namely augmentation and nutrition, which is proper to the living, he treats of every grade of life or of the soul which provides it, and he ascends even to the grade of intellective life, which is found in our soul; and of this he treats in the books On the Soul. And thus through these four parts the whole of natural science is divided.

The first part of philosophy, as we have said, treats of mobile being in common. Since it was propounded scientifically by Aristotle, who is most especially regarded in science, his order must be kept before one's eyes when considering the subject.

BOOK I.

Therefore, to consider mobile being in common, he first sets forth certain preludes and principles, whence we might be able to discern what a natural being is, and what kind of being it is; for that will especially be established from the quasi-elemental principles of such a being. The ancients held various opinions about these principles, proposing diverse origins and principles of natural things. Here, he does not call principles a cause (through which a natural being comes to be) but that from which natural being is and into which it is resolved—whether considering natural being in its becoming insofar as it is generated, or in its fact of being insofar as it is composed of those principles. And thus for composition he assigns two principles, namely, matter and form; for generation, however, he adds a third principle, namely, privation, insofar as in generation one proceeds from the non-being of a form, or its privation, as from the term-from-which to the being of the form as to the term-to-which in some subject or matter. And this he explains in the first book.

BOOK II.

Second, the Philosopher propounds those things which ought to be presupposed in this science concerning the subject and the principles or means by which this science demonstrates. The subject is that of which nature consists, which arises from the principles explained in the first book, namely, from matter and form. Thus he treats of nature. The principles or means, by which one must demonstrate concerning this natural being or concerning nature, are the four causes: namely, material, formal, efficient, and final; for on these depend all things which are demonstrated concerning this subject. And this he does in the second book.

BOOK III.

Third, he proceeds to explain the proper passion of this natural being, which is motion, from which it is most especially called "mobile being." The remaining books of the Physics are taken up by this consideration, and its consideration is twofold: one according to itself absolutely, the other comparatively or with respect to extrinsic things upon which it depends, namely, to movers and to mobile things. Concerning the first consideration, he first treats of motion in common and its properties, then he treats of motion in particular regarding its species and parts, through which it is divided or continuous.

In the third book, then, he treats of motion in common and those things which intrinsically accompany and follow it. He does this first by explaining the definition of motion, then action and passion which accompany it and without which there is no motion, and thirdly the nature [ratio] of the finite and the infinite, which necessarily and intrinsically follows upon motion by reason of the continuity and succession of parts.

BOOK IV.

In the fourth book, he treats of the extrinsic properties of motion. There are two things by which motion is extrinsically affected and measured: namely, place and time, as St. Thomas also notes at the beginning of the fourth book of the Physics.¹ For motion is measured on the part of the mobile thing by place, and on the part of its duration by time. By treating of place, he also treats of the void, which is its privation.

BOOKS V AND VI.

Having considered motion and its properties, both intrinsic and extrinsic, he treats next in books 5 and 6 of its divisions. First, of course, he treats of the essential and intrinsic division by species; second, of the division according to the parts of the quantity of the continuum in which the motion is exercised.

He follows the first division in book 5, showing that three species of motion are given: local, alteration, and augmentation. And similarly he treats of the unity of motion, both specific and individual, and of the contrariety of motions, because contrariety is given among diverse species.

The second division of motion, namely according to its continuous parts, he treats in book 6. There he treats of the divisibility of motion, both by reason of the medium through which it is moved and by reason of the time in which it is moved, and he treats of how a continuum is not composed of indivisibles alone, and consequently neither is motion. All these things belong to the consideration of motion (from the third book unto the sixth) according to those things which belong to it absolutely, both in itself and in its properties and divisions.

BOOKS VII AND VIII.

It remains in the remaining books to explain those things which belong to motion comparatively as to movers and to mobile things. Book 7 considers the order of mobile things to movers by descending all the way down to the first motion and the first mover, because a process is not given to infinity. And similarly he considers the condition required between the mover and the mobile, namely, that they be simultaneous and near, and consequently he compares motions among themselves as to velocity and slowness.

Second, in book 8 he considers the quality of the first motion and the first mover, where the consideration of mobile being comes to a halt, showing that the first mover is sempiternal, wherein is also treated concerning the eternity of the first motion and the eternity of the universe produced by it. Similarly, he shows that the first motion is a local and circular motion, and finally that the first mover is of infinite power and lacks magnitude, and is thus incorporeal and indivisible. We must treat of all these things at present according to this very order of the books of Aristotle.

But a question must be put forth beforehand about the science of philosophy itself (as a prefatory question) and about the order which must be kept in the process of cognition and science.

At present, we omit many things which are usually disputed concerning the science of philosophy, since they can be made known easily from the resolution given in the prefatory question of our book on logic¹ and in the last question of our book on the Posterior Analytics.² Such omitted points include whether philosophy is necessary for us, whether it is a science, whether practical or speculative, and other like questions which are resolved by similar resolution. For it is established that philosophy is necessary for us for a correct and scientific scrutiny of natural things. That it is indeed a science is established from many demonstrations which will be made in the due course of this science; and that it is also speculative is established both from the end of this science, which is the investigation and knowledge of natural truths, not the making of them, and from the principles by which it proceeds, which show the truth in a resolutive mode, rather than teaching how to manufacture it in a compositive mode.

Wherefore only three things remain to be explained which are proper to this science. First, its formal and material object, whatever it may be. Second, its unity, whether it is of one indivisible species, or whether it is divided into diverse species according to diverse objects (e.g., whether that which treats of the heavens is diverse in species from that which treats of generation or of the soul, or whether all this is of one species). Third, the order of knowing, what is first known by our intellect, which Aristotle treated by way of a preface in this first book.