Ethics asks what a person ought to do, and why that answer binds them. Every other question in the field grows out of that one: what makes an action right, what makes a life good, and where the authority behind either claim comes from.

The three standard answers

Western moral philosophy has settled into three broad families, and almost every modern argument is a variant of one of them.

  • Virtue ethics asks what kind of person you are becoming. Aristotle argued in the Nicomachean Ethics (c. 340 BC) that the good life is activity of the soul in accordance with excellence, and that excellence is built by habit rather than chosen in a moment.
  • Deontology asks what duty requires. For Kant, an action has moral worth when it is done from duty, and the test of a duty is whether you could will everyone to act on it.
  • Utilitarianism asks what the consequences are. John Stuart Mill held that actions are right in proportion as they tend to promote happiness.

These disagree about where moral weight sits: in the agent, in the act, or in the outcome. Most real disputes about a hard case turn out to be disputes about which of those three to look at first.

Meta-ethics and normative ethics

Normative ethics asks which actions are right. Meta-ethics asks what moral claims are doing in the first place — whether "cruelty is wrong" states a fact, expresses an attitude, or reports a convention. Hume sharpened this in the Treatise of Human Nature (1739) by noticing that writers slide from statements about what is to statements about what ought to be without explaining the move. That observation became the is-ought gap.

A third branch, applied ethics, takes the machinery to particular questions: medicine, war, business, animals. It is where the abstract families meet cases that will not sit still.

Why the disagreement persists

The three families rarely disagree about ordinary cases. They diverge at the edges — when keeping a promise causes harm, or when a small injustice buys a large benefit. Philosophers use those edge cases deliberately, because a theory shows its shape where it is under strain.