Ethics — The branch of philosophy that investigates the rational foundations of human action, the criteria of good and evil, and the norms that guide conduct. The word comes from the Greek ēthikē, derived from ēthos, which denotes at once the character of a person and the custom or habit of a group — an ambiguity Aristotle himself exploits when he shows that virtue is formed through the repetition of good actions until it becomes a stable disposition. The Latin mos/mores (custom), the source of “morality,” carries the same sense. Though often used interchangeably, ethics and morality are commonly distinguished: morality is the set of rules actually operative in a society, whereas ethics is the critical reflection upon those values. Ethics asks not merely “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 of life. In modernity, Kant grounds ethics in unconditional duty as expressed by the categorical imperative — to act only on a maxim one could will as a universal law — a deontological stance that judges action by its form rather than its results. By contrast, the utilitarianism of Bentham and Mill is a consequentialist ethics, evaluating acts by 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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