Western philosophy began when one man declared that everything is water
Thales of Miletus was wrong about water, but he reached his answer by observing and reasoning rather than repeating myths. That shift from story to argument launched Western philosophy, and within a few generations Greek thinkers had proposed infinity, number, fire-like flux and four elements as the root of all things.
The word philosophy comes from Greek for love of wisdom, and in antiquity it swallowed subjects we now treat separately: Aristotle wrote on physics, astronomy and biology as well as ethics. The pre-Socratics asked what the arche, the first principle, of the world might be. After Thales, born around 625 BC, his student Anaximander proposed the apeiron, the boundless, while Anaximenes preferred air. Pythagoras of Samos, who settled in southern Italy, taught that all is number; his followers' discovery of musical intervals brought harmony into philosophy, and they believed souls pass into new bodies.
Parmenides insisted reality is single and unchanging, so change must be illusion, and Zeno of Elea devised his paradoxes of motion to back him up. Heraclitus took the opposite line, saying everything flows and no one steps into the same river twice. Empedocles split the difference with four elements stirred by Love and Strife. The Sophists, teachers of rhetoric, trained students to argue either side; Protagoras declared that man is the measure of all things.
Socrates changed direction after a friend was told by the Delphic oracle that no Athenian was wiser. Trying to test that claim, he questioned anyone who would talk, developing the method that bears his name and focusing on justice, virtue and the good life. He wrote nothing; we know him through Plato and Xenophon. Convicted of impiety and corrupting the young, he refused a chance to escape and drank hemlock in 399 BC.
His pupils scattered into rival schools. Plato founded the Academy and tied virtue to knowledge. The Cynics of Antisthenes rejected wealth and fame to live simply by nature, while Aristippus's Cyrenaics called immediate pleasure the highest good. Aristotle, Plato's student, founded the Peripatetic school and built the first logic that tried to classify every valid syllogism. Later came Stoicism, Epicureanism and Neoplatonism, whose founder Plotinus argued that mind precedes matter.
Source: Western philosophy
