a) Aristotle's metaphysical production has given rise to some important literary problems. The principal one centers on the formation of the eponymic Metaphysics, a collection in fourteen books containing his essential thought on first philosophy. This collection, it is commonly realized, did not originate as a continuous composition, from one time and one effort. It is rather a compilation of writings, or parts thereof, which date from various periods of Aristotle's career. The present arrangement, moreover, stems not from himself but from his posthumous editors. For our purpose, however, it is not necessary, nor would it be feasible, to go into the literary problem the compilation poses; but we should at least indicate the basic groupings within the work as it now stands, since this bit of information is almost indispensable for intelligent reading of the whole.
Books A, B, r, E. Z, H. 0 (1, 3, 4, 6, 7, 8, 9) constitute a sufficiently coherent body to be considered, for all practical purposes, a continuous development. Treated, after some preliminaries, are the following problems: the object of metaphysics (being as being, and the things pertaining to being as being); substance (the fundamental mode of being); act and potency. Books I and A (10,12) appear to have been independent compositions, yet in the plan anticipated by Aristotle they follow logically after the preceding group. Book I deals with the problem of the one and the many; Book A, after some recapitulatory chapters, with the primary substance (the first mover). Books M and N (13,14), though probably of different date, are closely parallel in content; both present a searching criticism of the (Pythagorean) theory of numbers and the (Platonic) theory of Ideas. This leaves Books a, A, and K (2, 5, ii), which it is difficult to fit into a pattern with the rest. As to content, Book a (2), whose authenticity is debated but generally accepted, deals mainly with the problem of nonregression to infinity; A (5) is scarcely more than an analytical lexicon, though a very valuable one, of philosophical notions, pertaining mostly to physics and metaphysics; K (11) is a gathering of extracts from the Physics plus abridgments from B, r, and E of the Metaphysics.
b) Further complication awaits us in turning to St. Thomas, whose metaphysical work, on the whole, falls to two principal deposits.
The first is, of course, his Commentary on Aristotle's Metaphysics, the first twelve books, to be exact. Concerning this Commentary, the opinion has been advanced that St. Thomas was only clarifying Aristotle's thought, refraining his own. The opinion is untenable. In the Commentary St. Thomas, it must be maintained, was not only spelling out Aristotle but also philosophizing on his own. What is true is that the Commentary of its very nature does not escape the hobbles and hitches of Aristotle's text, which, while perhaps sufficiently articulated, yet lacks that perfectly organic composition one might wish. In any event, the Commentary is not the complete metaphysical thought of St. Thomas. There are other developments of his on the subject, more uniquely his own, and these also must be appreciated before one can see his metaphysics in all its richness and amplitude.
The second deposit in point is found in his theological study of God as one (De Deo uno). Here again all is not in one place, though all is very much of a piece. There is the ample section in the Summa theologiae,29 a whole book of the Contra Gentiles,30 and an impressive array of parallel passages in various smaller works.31 In these compositions St. Thomas' thought is expressed more at large than in the Commentary, and its scope and penetration grow accordingly. But here, on the other hand, it is interwoven with the fabric of supernatural (as against natural) theology.
St. Thomas may be said to offer a twofold version of metaphysics: one whose source and methodology is purely philosophical but whose structure is noticeably grafted and underdeveloped; the other, more organic, excels in height and depth but has, for us, the disadvantage of being incorporated in theological dissertation. Between the two, we hasten to add, there is remarkable coherence of doctrine, albeit the preoccupations and the standpoints are not the same. In practice, nevertheless, the expositor of St. Thomas' metaphysics must, to keep his account orderly, make a choice. Either he adopts the strictly philosophical point of view and from the being of experience progresses to the being that is God (as in the Commentary), or he takes the theological approach, a more synthetic task, according to which God stands at the beginning of his inquiry and created being is elucidated throughout as his handiwork (as, for example, in the Summa Theologiae).
c) Our choice is the former. While not disregarding altogether the invaluable complement of the theological writings, our study follows the philosophical path of the Metaphysics and the Commentary. It begins, accordingly, with the being of immediate experience and advances by degrees to the being that is God, the natural culmination, it will appear, of the entire work as well as the keystone that firms it together. That done, we shall have an adequate view of St. Thomas' metaphysics but not, be it said, an exhaustive one. For such a view, it would be necessary to go considerably further. The steps of our inquiry would need to be retraced and the basic positions we have established gone over again to be propounded a second time, but from the perspective of the theological treatment of God. The result would be, so to speak, a downward metaphysics, from God to creature, in contrast to the upward manner of the present work. To achieve it, however, would have made a more formidable task, and a more formidable volume, than lay to the purpose.