In philosophic idiom the word metaphysics denotes the higher branch of philosophy, the part that seeks after the most basic principles of things, their ultimate ground and nature. The word itself was first suggested by Andronicus of Rhodes (2nd century B.C.), the first redactor of Aristotle's complete works. Under the heading of Meta ta Phusika (lit. "after the Physcals") Andronicus placed a group of fourteen books (long "chapters," in modern description) whose content seemed to follow logically after the books of the Physics. Yet Aristotle himself had never spoken of these fourteen books or of their content as "metaphysics" but always as "first philosophy" or as "theology." The proper object of metaphysics, or its special reference of inquiry, in Aristotelian thought is, we shall see, being as being together with its properties. But the proper object, or at least this determination of it, is not clear-cut from the outset; indeed, a first survey of the Metaphysics reveals what amounts to three successive conceptions of the science, yet on the face of it there is no firm indication how they are to be integrated. St. Thomas, who accepts the Aristotelian view of the proper object, was aware that the threefold conception lay, or so it seemed, unresolved and went to some pains to clarify it; which he does in the Prologue to his Commentary. Among the points made are these: First, in contrast to other sciences, which explore only the more immediate principles and causes, metaphysics stands forth as the science of first causes and first principles. This definition echoes the general notion of science, for in the Aristotelian tradition it is axiomatic that science, all true science, consists in knowledge through causes: cognitio per causas. It is from this point of view that metaphysics is properly called "first philosophy," the conception that predominates in Book A of Aristotle's treatise.
Secondly, metaphysics can also be envisioned as the science of being as being and of the attributes (or properties) of being as being, a view of the science which points to the comprehensiveness of its object. Unlike other sciences, each of which considers only a particular province of being, metaphysics, the science of being as being, embraces all being. This conception is developed in Book r and appears to be upheld in the sequel. It is the conception which corresponds to the word "metaphysics" in its proper sense.
Thirdly, metaphysics can be defined as the science of the immobile (i.e. the motionless or unchanging) and the separate (i.e. from matter). In this it differs from the philosophy of nature or physics in the Aristotelian sense and from mathematics; for the proper object of these sciences always retains some mode of materiality. Moreover, among beings that are separate (i.e. free) from matter must be reckoned God, who is indeed furthest removed. Consequently, metaphysics understood as the science of the separate includes the study of God and is not improperly spoken of as "theology," the conception that preponderates in Book E and thereafter.
St. Thomas' Prologue is, however, too important to be dismissed with passing summary; it should be read clear through with close attention. Note especially his analysis of the primacy that metaphysics enjoys among the sciences. Metaphysics, he observes, governs and directs all other sciences, and this in virtue of the principle that the most intellectual science is the ruling science. But then, why should metaphysics be the most intellectual science? The answer is because its object are the "most intelligibles," beings and modes of being of the highest intelligibility. This notion "most intelligible" admits, however, of a threefold sense; and thereby hangs the threefold conception. For the explanation, here is St. Thomas himself: First, ["most intelligible" can be understood] from the viewpoint of the order of knowing; for those things from which the intellect derives certitude seem to be more intelligible. Therefore, since the certitude of science is acquired by the intellect knowing causes, a knowledge of causes seems to be intellectual in the highest degree. Hence that science which considers first causes also seems to be the ruler of the others in the highest degree.
Second, this phrase can be understood by comparing the intellect with the senses; for while sensory perception is a knowledge of particulars, the intellect seems to differ from sense by reason of the fact that it comprehends universals. Hence that science is pre-eminently intellectual which deals with the most universal principles. These principles are being and those things which naturally accompany being, such as unity and plurality, potency and act. Now such principles should not remain entirely undetermined, since without them a complete knowledge of the principles which are proper to any genus or species cannot be had. Nor again should they be dealt with in anyone particular science, for, since a knowledge of each class of beings stands in need of these principles, they would with equal reason be investigated in every particular science. It follows, then, that such principles be treated by one common science, which, since it is intellectual in the highest degree, will govern the others.
Third, this phrase can be understood from the viewpoint of the intellect's own knowledge. For since each thing has intellective power by virtue of being free from matter, those things must be intelligible in the highest degree which are altogether separate from matter .... Now those things are separate from matter in the highest degree which abstract not only from signate matter . . . but from sensible matter altogether; and these are separate from matter not only in their intelligible constitution [ratio], as the objects of mathematics, but also in being, as God and the intelligences [spirits]. Therefore the science which considers such things seems to be the most intellectual and the ruler and master of the others.1 These, then, are the various aspects to metaphysics: science of first principles and first causes (which is to say, wisdom), science of being as being, and science of what is utterly separate from matter. Our next step will be to examine these formulations in some detail, and thus provide a better understanding of the underlying notion in each case. To this end we shall, among other things, trace their development in Greek thought and observe how they align themselves with the course of that thought as a whole. So doing, we shall be reminded that Aristotle is not without ancestry, that though his metaphysical accomplishment is a triumph of discovery and elaboration in its own right, it may also be seen as the culminating synthesis of a metaphysical enterprise stretching back three centuries before him.