Ethics — From Greek ēthikē, derived from ēthos (character, custom). The branch of philosophy that investigates the rational foundations of human action, the criteria of good and evil, and the norms guiding moral conduct. Ethics is distinguished from morality — the set of rules operative in a given society — by its reflective and critical character: ethics asks not “what should I do?” but “why should I do it?” Aristotle inaugurates the discipline with the Nicomachean Ethics, centred on virtue (aretē) and happiness (eudaimonia) as the ultimate end. In modernity, Kant grounds ethics in unconditional duty (the categorical imperative), while utilitarianism (Bentham, Mill) anchors it in the principle of the greatest happiness for the greatest number. Contemporary ethics unfolds into metaethics (the nature of moral judgements), normative ethics (theories of right action), and applied ethics (bioethics, environmental ethics, professional ethics).
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