PhilosophyLogic and Metaphysics
Aristotle placed great emphasis in his school on direct observation of nature, and in science he taught that theory must follow fact. He considered philosophy to be the discerning of the self-evident, changeless first principles that form the basis of all knowledge. Logic was for Aristotle the necessary tool of any inquiry, and the syllogism was the sequence that all logical thought follows. He introduced the notion of category into logic and taught that reality could be classified according to several categories—substance (the primary category), quality, quantity, relation, determination in time and space, action, passion or passivity, position, and condition.
Aristotle also taught that knowledge of a thing, beyond its classification and description, requires an explanation of causality, or why it is. He posited four causes or principles of explanation: the material cause (the substance of which the thing is made); the formal cause (its design); the efficient cause (its maker or builder); and the final cause (its purpose or function). In modern thought the efficient cause is generally considered the central explanation of a thing, but for Aristotle the final cause had primacy.
He used this account of causes to examine the relation of form to matter, and in his conclusions differed sharply from those of his teacher, Plato. Aristotle believed that a form, with the exception of the Prime Mover, or God, had no separate existence, but rather was immanent in matter. Thus, in the Aristotelian system, form and matter together constitute concrete individual realities; the Platonic system holds that a concrete reality partakes of a form (the ideal) but does not embody it. Aristotle believed that form caused matter to move and defined motion as the process by which the potentiality of matter (the thing itself) became the actuality of form (motion itself). He held that the Prime Mover alone was pure form and as the "unmoved mover" and final cause was the goal of all motion.
Aristotle's ethical theory reflects his metaphysics. Following Plato, he argued that the goodness or virtue of a thing lay in the realization of its specific nature. The highest good for humans is the complete and habitual exercise of the specifically human function—rationality. Rationality is exercised through the practice of two kinds of virtue, moral and intellectual. Aristotle emphasized the traditional Greek notion of moral virtue as the mean between extremes. Well-being ( eudaemonia ) is the pursuit not of pleasure (hedonism) but rather of the Good, a composite ideal, consisting of contemplation (the intellectual life) and, subordinate to that, engagement in politics (the moral life). In the Politics, Aristotle holds that, by nature, humans form political associations, and he explores the best forms these may take. For Aristotle's aesthetic views, which are set forth in the Poetics, see tragedy.