When Plato died in 347 bc, Aristotle moved to Assos, a city in Asia Minor, where a friend of his, Hermias (died 345 bc), was ruler. There he counseled Hermias and married his niece and adopted daughter, Pythias. After Hermias was captured and executed by the Persians, Aristotle went to Pella, the Macedonian capital, where he became the tutor of the king\'s young son Alexander, later known as Alexander the Great. In 335, when Alexander became king, Aristotle returned to Athens and established his own school, the Lyceum. Because much of the discussion in his school took place while teachers and students were walking about the Lyceum grounds, Aristotle\'s school came to be known as the Peripatetic ("walking" or "strolling") school. Upon the death of Alexander in 323 bc, strong anti-Macedonian feeling developed in Athens, and Aristotle retired to a family estate in Euboea. He died there the following year.

Works

Aristotle, like Plato, made regular use of the dialogue in his earliest years at the Academy, but lacking Plato\'s imaginative gifts, he probably never found the form congenial. Apart from a few fragments in the works of later writers, his dialogues have been wholly lost. Aristotle also wrote some short technical notes, such as a dictionary of philosophic terms and a summary of the doctrines of Pythagoras. Of these, only a few brief excerpts have survived. Still extant, however, are Aristotle\'s lecture notes for carefully outlined courses treating almost every branch of knowledge and art. The texts on which Aristotle\'s reputation rests are largely based on these lecture notes, which were collected and arranged by later editors.

Among the texts are treatises on logic, called Organon ("instrument"), because they provide the means by which positive knowledge is to be attained. His works on natural science include Physics, which gives a vast amount of information on astronomy, meteorology, plants, and animals. His writings on the nature, scope, and properties of being, which Aristotle called First Philosophy (Protč philosophia), were given the title Metaphysics in the first published edition of his works (circa 60 bc), because in that edition they followed Physics. His treatment of the Prime Mover, or first cause, as pure intellect, perfect in unity, immutable, and, as he said, "the thought of thought," is given in the Metaphysics. To his son Nicomachus he dedicated his work on ethics, called the Nicomachean Ethics. Other essential works include his Rhetoric, his Poetics (which survives in incomplete form), and his Politics (also incomplete).

Methods

Perhaps because of the influence of his father\'s medical profession, Aristotle\'s philosophy laid its principal stress on biology, in contrast to Plato\'s emphasis on mathematics. Aristotle regarded the world as made up of individuals (substances) occurring in fixed natural kinds (species). Each individual has its built-in specific pattern of development and grows toward proper self-realization as a specimen of its type. Growth, purpose, and direction are thus built into nature. Although science studies general kinds, according to Aristotle, these kinds find their existence in particular individuals. Science and philosophy must therefore balance, not simply choose between, the claims of empiricism (observation and sense experience) and formalism (rational deduction).

One of the most distinctive of Aristotle\'s philosophic contributions was a new notion of causality. Each thing or event, he thought, has more than one "reason" that helps to explain what, why, and where it is. Earlier Greek thinkers had tended to assume that only one sort of cause can be really explanatory; Aristotle proposed four. (The word Aristotle uses, aition, "a responsible, explanatory factor" is not synonymous with the word cause in its modern sense.)

These four causes are the material cause, the matter out of which a thing is made; the efficient cause, the source of motion, generation, or change; the formal cause, which is the species, kind, or type; and the final cause, the goal, or full development, of an individual, or the intended function of a construction or invention. Thus, a young lion is made up of tissues and organs, its material cause; the efficient cause is its parents, who generated it; the formal cause is its species, lion; and its final cause is its built-in drive toward becoming a mature specimen. In different contexts, while the causes are the same four, they apply analogically. Thus, the material cause of