The earliest Greek thinkers directed their philosophical efforts almost entirely to the investigation of nature, of the world that meets the casual observer. For this reason tradition, following Aristotle's example, awards them the significant title "Physicists"; for from Thales (ca. 640-550 B.C.) to Empedocles (ca. 500-430 B.c.) and Anaxagoras (ca. 500-428 B.c.) Greek thought was primarily engaged in working out an interpretation of the physical universe. True, with Socrates (470-399) the sciences based on self-knowledge, such as logic and moral philosophy, experienced a growth that was scarcely less impressive; but these newer interests did not dampen the ardor of pursuit in the domain of nature. Plato, for example, wrote not only the Republic but also the Timaeus; and after Democritus (ca. 460-400 B.C.) Aristotle again took up, with renewed zest, the tradition begun by the Ionians.
In this initial burst of philosophical enthusiasm the human mind had not yet clearly marked off the various orders of knowledge, so that what these forerunners of Greek thought sought to achieve was as much a philosophy of nature as it was a science of nature. Doubtless, certain branches of knowledge, geometry and arithmetic for example, soon acquired an independent status because of the practical use to which they could be put; but in the study of nature the Greeks never made a sharp distinction between its philosophical and, as we should say, its scientific aspects. Consequently, in the study of Greek thought the separation of science and philosophy, if made at all, can only be made on a more-or-less basis. The Greeks, we have said, mostly ignored it.
Despite this lack of clear-cut definition as to object and method in each case, the fact remains that the first great strides in both the science and the philosophy of nature occurred in Greece at about the same time, from the seventh to the third century B.C. In the present volume, however, our aim is not to relate the scientific progress of these centuries. Our interest lies in the philosophical aspect of the accomplishment. More precisely, it is focused on the philosophy of nature evolved by Aristotle, since this is substantially the doctrine St. Thomas teaches.
But if for practical reasons we center our attention on Aristotle, we do not intend to obscure the fact - indeed, it cannot be overstressed - that his physical doctrine was not sprouted in an intellectual wilderness, without benefit of pioneers preparing the ground. On the contrary, Aristotle's physics is but the flowering that came after many generations of intensive growth and cultivation. To do justice to all these fertile speculations about nature that preceded and attended Aristotle's own thought woul require a study of its own. Our remarks along this line are admittedly sparse, but enough, we trust, to lend historical perspective to the pre-eminent system of Aristotle's. So much, at least, was necessary, if only because the Aristotelian doctrine, while complete in itself, does not assume full significance without some reference to the philosophical environment that, in one way or another, gave it source and sustenance.