Newton's work marks the turning point in the career of Aristotle's universe. Thenceforth, Aristotle's conception of the cosmos could no longer be regarded as a total explanation. To be sure, Newton himself was in many ways to be surpassed, for science marches on. But, as intimated before, the enormous progress since his day should not blind us to the greatness of his achievement, even from the strictly scientific point of view.
As for Aristotle, though his sway has come and gone - I am speaking of the natural sciences and astronomy - history must nevertheless regard him as one of the great scientific geniuses of mankind. His original contributions, especially in the natural sciences, cannot be denied. In fact, one has to wait almost till the eighteenth century before meeting with new advances in this field - a tribute to his abundant genius, to his thoroughness and penetration. Considering what he had to work with, the structure of his scientific thought was neither more nor less arbitrary than was, for their time, that of Descartes or Newton.
Some authors, while acknowledging Aristotle's influence, take a less benign view of it. This very influence, they contend, was responsible for the long scientific sterility that allegedly set in after Aristotle. Like most sweeping criticisms, this is open to challenge in more ways than one. For example, Euclid, Archimedes, Ptolemy, Pappus, Diophantus, these, to which others could be added, form an imposing array of scientific pioneers, and all of them belong to the immediate centuries after Aristotle. With such names to distinguish it, was this an epoch of scientific sterility?
Concerning the relative decline of science in the early Middle Ages, to blame this on Aristotle or, for that matter, on the medievals does little justice to history. If one remembers the repeated onslaughts of the Barbarian invader, it would seem far more realistic, as well as more appropriate, to esteem than to disesteem the medieval scientific legacy. And when from the fifteenth through the sixteenth century science again reached a development that compared favorably with its growth among the Greeks, the Aristotelian formulas and axioms repeated by the Schoolmen in the lecture halls do not appear to have stifled the spirit of original inquiry. On the contrary, this was again a time of real geniuses, a time of such productivity that in less than a century a whole new order of scientific thought had established itself.
To come to a more particular point. Aristotle's physics or philosophy of science (in the modern sense) is often opposed to the philosophy of the Pythagorean school, meaning a philosophy built on number or quantity. Aristotle's physics, it is said, stresses the qualitative side of nature to the exclusion of its quantitative aspects, the implication being that only a quantitative reduction of nature brings results. Here again a more discriminating appraisal would put the matter in a different light. Aristotle affirms the primacy of quantity over the other accidents; it is first in the order of accidents, the immediate disposition of substance. He also maintains the primacy of local (quantitative) motion. Definitely, then, and by his own showing, Aristotle is far from underrating the quantitative aspect of phenomenal nature. His system of physical motion could not, it is true, survive. Nevertheless, it was a practical, and not just a theoretical, explanation of celestial and terrestrial motions; for his day, and long after, it was on the whole adequate.
What Aristotle did and could not envisage was the enormous possibilities that lay in the mathematical exploration of the corporeal world; the tools for this manner of attack, so prominent in modern scientific inquiry, had not yet been forged. Yet, what mathematics there was he knew about; for as a member of the Academy he took part in its discussions on number. So removed from reality they generally were, however, that a man of Aristotle's scientific bent must often have left disappointed. Aristotle's interest was anchored to reality; probing it qualitatively, not to say quantitatively, he was far more the true scientist than were the armchair number-philosophers of the Academy.
But whatever the merits of his scientific accomplishment, Aristotle's most lasting success in the domain of nature is his philosophy of nature, the probings and findings underneath the surface, the unveilings round the core of physical reality. His conception of the principles of mobile being, his theory of causes, his ideas on change, on finality, on determinism, his analysis of motion and its primary concomitants of space (or place) and time, these matters still command the attention of the serious philosophical investigator of nature, because seen in their true light they have lost none of their substantive correctness.
A few simple facts of universal experience sustain this philosophical edifice. There are change, and becoming, and multiplicity in the physical world. There are concrete individuals which come and go, are born and die. Things of nature, they have quantity and quality. These facts of experience, which bear not mistrust, are the piers and pillars controlling the whole structure. Science, no doubt, will continue to find new theories for itself, and remake or discard old ones. But one cannot imagine that science will ever find us a universe from which the aforesaid essentials are missing. Improvements, certainly, can be made at many points in Aristotle's thought, improvements and additions. But this is face lifting. In foundation, in essential cast, the philosophy of nature that Aristotle gave to the world is and bids fair to remain intact.