Aristotle (384–322 BCE) was Plato's student, but his surviving work ranges far beyond a reaction against Plato: logic, ethics, politics, metaphysics, rhetoric, poetry, psychology, and detailed biological investigation.

Big idea: To understand a thing, Aristotle often asks for several kinds of explanation at once rather than searching for one single cause.

His famous four causes are:

• material cause — what it is made from;
• formal cause — the organization/form that makes it this kind of thing;
• efficient cause — what brings it about or changes it;
• final cause — the end/function toward which it is directed.

Modern science generally does not treat nature as universally goal-directed in Aristotle's sense, but functional explanation remains familiar in biology and engineering when used carefully.

In ethics, the central idea is eudaimonia — human flourishing, not merely a passing feeling of happiness. Character is formed through habituation: we become courageous, generous, or just partly by repeatedly practicing the relevant kinds of action. Virtue often involves finding the appropriate mean relative to circumstances, guided by practical wisdom (phronesis).

“The golden mean” is frequently caricatured as “always choose the moderate middle.” Aristotle's point is not arithmetic compromise: courage is a mean between cowardice and rashness, but the right action depends on situation, motive, person, and judgment.