Cursus Philosophicus Thomisticus, Prima Pars Philosophiae Naturalis

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.