Nature

All these thinkers pale in comparison with Aristotle (384–322 B.C.E.), the greatest classical theorist. Aristotelian ideas of nature dominated Western civilization until the scientific revolution of the seventeenth and eighteenth centuries. So pervasive is his influence that some believe Western intellectual history is little more than footnotes to his work. Only a partial description showing Aristotle's continuing influence can be included here.

First, Aristotle introduced the category of cause as a key explanatory feature for theorizing nature. He understood the diverse phenomena and different kinds in nature in terms of four causes: the formal, material, efficient, and final. Aristotle's account of causation surpasses the theories of his predecessors. For example, his notion of material cause chimes with the atomism of Leucippus and Democritus, and yet the atoms themselves are neither a final cause, since they have been set into original motion, nor an efficient cause, since they can be rearranged by other factors, including human agency.

Second, Aristotle argued that all motion is a consequence of an original, unmoved mover. Without the unmoved mover any causal sequence would entail an infinite regress. Aristotle's notion of an unmoved mover, while driven by his logical commitment to avoiding motion that cannot be explained, resonates not only with earlier Hebraic conceptions of a creator god but also with Parmenidean commitments to a final rational explanation for all that is, was, or ever will be. It also resonates with the Heraclitean stream of influence: natural processes and creatures move.

Third, Aristotle offered a theoretical account of living nature manifesting a sensitivity to the explanatory and descriptive requirements of the behavior of plants and animals. These motions could not be explained in the same way as those of inanimate objects. While not an evolutionary thinker in modern terms, he recognized the diversity of natural kinds with their characteristic patterns of reproduction and growth.

The theoretical legacy of the Greeks is highly significant. While it is an exaggeration to say that the period between the fall of Rome and the Middle Ages was a conceptual wasteland, and while descriptive accounts of nature flourished (in astronomy, for example), there were few developments beyond Aristotelian ideas. The Middle Ages brought some conceptual refinements, but no paradigmatic breakthroughs. For example, William of Ockham (c. 1285–1349?) deduced that a simpler explanation was to be preferred to a more complicated explanation when the explanatory power was equal—a logical principle of parsimony known as Ockham's razor. But it is the theorizing of classical Greek civilization that lives on, even if implicitly.