Aristotle (384–322 BC)

Greek philosopher who advocated reason and moderation. He maintained that sense experience is our only source of knowledge, and that by reasoning we can discover the essences of things, that is, their distinguishing qualities. In his works on ethics and politics, he suggested that human happiness consists in living in conformity with nature. He derived his political theory from the recognition that mutual aid is natural to humankind, and refused to set up any one constitution as universally ideal. Of Aristotle's works, around 22 treatises survive, dealing with logic, metaphysics, physics, astronomy, meteorology, biology, psychology, ethics, politics, and literary criticism.

Aristotle was born in Stagira in Thrace and studied in Athens, where he became a distinguished member of the Academy founded by Plato. He then opened a school at Assos. At this time he regarded himself as a Platonist, but his subsequent thought led him further from the traditions that had formed his early background and he was later critical of Plato. In about 344 BC he moved to Mytilene in Lesvos, and devoted the next two years to the study of natural history. Meanwhile, during his residence at Assos, he had married Pythias, niece and adopted daughter of Hermeias, ruler of Atarneus.

In 342 BC he accepted an invitation from Philip II of Macedon to go to Pella as tutor to Philip's son Alexander the Great. In 335 BC he opened a school in the Lyceum (grove sacred to Apollo) in Athens. It became known as the ‘peripatetic school’ because he walked up and down as he talked, and his works are a collection of his lecture notes. When Alexander died in 323 BC, Aristotle was forced to flee to Chalcis, where he died.

Among his many contributions to political thought were the first systematic attempts to distinguish between different forms of government, ideas about the role of law in the state, and the conception of a science of politics.

In the Poetics, Aristotle defines tragic drama as an imitation (mimesis) of the actions of human beings, with character subordinated to plot. The audience is affected by pity and fear, but experiences a purgation (catharsis) of these emotions through watching the play. The second book of the Poetics, on comedy, is lost. The three books of the Rhetoric form the earliest analytical discussion of the techniques of persuasion, and the last presents a theory of the emotions to which a speaker must appeal.

In the Middle Ages, Aristotle's philosophy first became the foundation of Islamic philosophy, and was then incorporated into Christian theology; medieval scholars tended to accept his vast output without question. Aristotle held that all matter consisted of a single ‘prime matter’, which was always determined by some form. The simplest kinds of matter were the four elements – earth, water, air, and fire – which in varying proportions constituted all things. According to Aristotle's laws of motion, bodies moved upwards or downwards in straight lines. Earth and water fell, air and fire rose. To explain the motion of the heavenly spheres, Aristotle introduced a fifth element, ether, whose natural movement was circular.

His major writings on cosmology, or astronomy, are brought together in the four‐volume Peri ouranou/On the Heavens. Aristotle rejected the notion of infinity and the notion of a vacuum. A vacuum he held to be impossible because an object moving in it would meet no resistance and would therefore attain infinite velocity. Space could not be infinite, because in Aristotle's view, the universe consisted of a series of concentric spheres which rotated around the centrally placed, stationary Earth. If the outermost sphere were an infinite distance from the Earth, it would be unable to complete its rotation within a finite period of time, in particular within the 24‐hour period in which the stars, fixed, as Aristotle believed, to the sphere, rotated around the Earth.

Aristotle's work in astronomy also included proving that the Earth was spherical. He observed that the Earth cast a circular shadow on the Moon during an eclipse and he pointed out that as one travelled north or south, the stars changed their positions. Aristotle overestimated the Earth's diameter by only 50%.

Aristotle saw nature as always striving to perfect itself. The principle of life he termed a soul, which he regarded as the form of the living creature, not as a substance separable from it. The intellect, he believed, can discover in sense impressions the universal, and since the soul thus transcends matter, it must be immortal. Art embodies nature, but in a more perfect fashion, its end being the purifying and ennobling of the affections. The essence of beauty is order and symmetry. Aristotle also first classified organisms into species and genera.

The genuine writings of Aristotle, as usually cited, are as follows:Organon (comprising ‘Katēgoriai/Categories’, ‘Peri hermēneias/On Interpretation’, ‘Topika/Topics’ and its supplement ‘Peri sophistikōn elegchōn/Sophistical Refutations’, ‘Analytika protera/Prior Analytics’, and ‘Analytika hystera/Posterior Analytics’);Physikē/Physics;Peri ouranou/On the Heavens;Peri geneseōs kai phthoras/On Generation and Corruption;Meteōrologika/Meteorology;Peri psychēs/On the Soul (Latin translation De anima);Parva naturalia (comprising ‘Peri aisthēseōs/On Sense and Sensible Objects’, ‘Peri mnēmēs kai anamnēseōs/On Memory and Recollection’, ‘Peri hypnou kai egrēgorseōs/On Sleep and Waking’, ‘Peri enypniōn/On Dreams’, ‘Peri tēs kath hypnon mantikēs/On Divination in Sleep’, ‘Peri makrobiotētos kai brachybiotētos/On Length and Shortness of Life’, ‘Peri neotētos kai gērōs/On Youth and Old Age’, ‘Peri zōēs kai thanatou/On Life and Death’, and ‘Peri anapnoēs/On Respiration’);Peri ta zōa historiai/History of Animals;Peri zōōn kinēseōs/Movement of Animals;Peri zōōn geneseōs/Generation of Animals;Ta meta ta physika/Metaphysics;Ethika Eudēmeia/Eudemian Ethics;Ethika Nikomachaeia/Nicomachaean Ethics;Politika/Politics;Athēnaiōn politeia/The Athenian Constitution (incomplete);Technē rhētorikē/Rhetoric; and Peri poētikēs/Poetics (incomplete).