Plato would have said that a red object is red because it participates in the form, or perfect idea, of “Red.” Aristotle, on the other hand, would have called that nonsense. A red object is red, he would have insisted, because after repeated experience with red objects, humans eventually identified a color called “red.” If this seems like mere common sense, it is a mark of how much Aristotle has affected the Western, and particularly American, approach to knowledge.
In order to explain how things existed, Aristotle identified four causes—material, efficient, formal, and final. A house, for instance, is made up of various items such as wood and glass, which are its material cause, or what it consists of. But these have to be put together by construction workers, who as the shapers of the house are its efficient cause. Yet they must have a blueprint to go by, a design or formal cause. Even if all these causes are present, there must also be a reason why the house was built—e. g., for people to live in it—and this is the “why,” or the final cause.
People in modern times are accustomed to talking about “actualizing” their “potential.” This idea is also a legacy of Aristotle, who maintained that the physical world is not fixed, as Parmenides had claimed; rather, it is constantly changing, and every living object contains the potential for change. Thus an acorn holds the potentiality for an oak. All beings are part of an ascending order of potentialities, he believed, the highest of which is God.
In contrast to Plato's emphasis on the universal—that is, on the forms, which exist in some heavenly realm and are the mystical essence of things on earth—Aristotle was concerned with particular and individual things. He believed that the goal of the individual person was not, as Plato claimed, to rise above the physical, but simply to be happy.
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