Aristotelianism is a school or tradition of philosophy from the Socratic (or Classical) period of ancient Greece, that takes its defining inspiration from the work of the 4th Century B.C. philosopher Aristotle.
His immediate followers were also known as the Peripatetic School (meaning itinerant or walking about, after the covered walkways at the Lyceum in Athens where they often met), and among the more prominent members (other than Aristotle himself) were Theophrastus (322 - 288 B.C.), Eudemus of Rhodes (c. 370 - 300 B.C.), Dicaearchus (c. 350 - 285 B.C.), Strato of Lampsacus (288 - 269 B.C.), Lyco of Troas (c. 269 - 225 B.C.), Aristo of Ceos (c. 225 - 190 B.C.), Critolaus (c. 190 - 155 B.C.), Diodorus of Tyre (c. 140 B.C.), Erymneus (c. 110 B.C.) and Alexander of Aphrodisias (c. 200 A.D.).
Aristotle developed the earlier philosophical work of Socrates and Plato in a more practical and down-to-earth manner, and was the first to create a comprehensive system of philosophy, encompassing Ethics, Metaphysics, Aesthetics, Logic, Epistemology, Politics and Science. He rejected the Rationalism and Idealism espoused by Platonism, and advocated the characteristic Aristotelian virtue of "phronesis" (practical wisdom or prudence). Another cornerstone of Aristotelianism is the idea of teleology (the idea that all things are designed for, or directed toward, a final result or purpose).
Aristotelian Logic was the dominant form of Logic until 19th Century advances in mathematical logic, and as late as the 18th Century Kant stated that Aristotle's theory of logic completely accounted for the core of deductive inference. His six books on Logic, organized into a collection known as the "Organon" in the 1st Century B.C., remain standard texts even today.
Aristotle's works on Ethics (particularly the "Nicomachean Ethics" and the "Eudemian Ethics") revolve around the idea that morality is a practical, not a theoretical, field, and, if a person is to become virtuous, he must perform virtuous activities, not simply study what virtue is. The doctrines of Virtue Ethics and Eudaimonism reached their apotheosis in Aristotle's ethical writings. He stressed that man is a rational animal, and that Virtue comes with the proper exercise of reason. He also promoted the idea of the "golden mean", the desirable middle ground, between two undesirable extremes (e.g. the virtue of courage is a mean between the two vices of cowardice and foolhardiness).
Aristotelian Metaphysics and Epistemology largely follow those of his teacher, Plato, although he began to diverge on some matters. Aristotle assumed that for knowledge to be true it must be unchangeable, as must the object of that knowledge. The universe therefore divides into two phenomena, Form (the abstract and unobservable, such as souls or knowledge) and Matter (the observable, things that can be sensed and quantified), and these two phenomena are different from, but indispensable to, each other. Aristotle's conception of hylomorphism (the idea that substances are forms inhering in matter) differed from that of Plato in that he held that Form and Matter are inseparable, and that matter and form do not exist apart from each other, but only together.
Aristotle's theory of Politics emphasizes the belief that humans are naturally political, and that the political life of a free citizen in a self-governing state or "polis" (with a constitution which is a mixture of leadership, aristocracy and citizen participation) is the highest form of life. Aristotelian ideals have underlain much modern liberal thinking about politics, the vote and citizenship.
Although much of Aristotle's work was lost to Western Philosophy after the fall of the Roman Empire, the texts were reintroduced into the West by medieval Islamic scholars like Averroes and Maimonides. Just as these Muslim philosophers reconciled Aristotelianism with Islamic beliefs, St. Thomas Aquinas was largely responsible for reconciling Aristotelianism with Christianity, arguing that it complements and completes the truth revealed in the Christian tradition. It became the dominant philosophic influence on Scholasticism and Thomism in the early Middle Ages in Europe.
The distinctively Aristotelian idea of teleology was transmitted through the German philosophers Christian Wolff (1679 - 1754) and Immaneul Kant to Georg Hegel, who applied it to history as a totality, resulting in turn in an important Aristotelian influence upon Karl Marx.
The lasting legacy of Aristotelianism can be seen in the works of contemporary philosophers such as John McDowell (1942 - ), Hans-Georg Gadamer (1900 - 2002) and Alasdair MacIntyre (1929 - ).