Deontological ethics is a family of moral theories that judge actions by duty and rules rather than by outcomes. In this view, an act can be morally required because of some characteristic of the act itself—for example, keeping a promise—even when the consequences are not the best possible.
The approach is often contrasted with consequentialism (teleological ethics), which evaluates actions by the value of what they produce. Immanuel Kant’s ethics is a classic deontological system: he held that a good will acts from respect for moral law, expressed in the categorical imperative to act only on maxims one could will as universal law.