Ethics is the study of human conduct or in other words the study of moral behavior. All humans use ethics in their daily actions and decisions, but not many have the opportunity to probe into the core of ethics. When Socrates said in 399 B.C., "The unexplained life is not worth living" he was encouraging man to examine his way of life and ways of moral decision making. Ethics not only aims to discover the rules that should govern a moral life, but the goods one should aim to acquire in their life time. Ethics aims to explain why and how man acts the way he does and to shape the way man lives and acts,. Some philosophers say that reason is the criterion for making moral judgments, others say that duty and obligation rule moral decisions. Eighteenth century philosopher David Hume gave a different outlook on what makes man act the way he does. Hume takes an almost Epicurean stance and proclaims that man's passions overrule reason and direct man's moral actions and judgments. Moral judgments are manifestations of human sentiments and passions.
Hume states that the passions are the only way to understand morality. The nature of moral values is to be discovered through the passions. Hume rejects that reason is the criterion for moral judgments, and bases most of his "Treatise of Human Nature" on refuting reason as the basis for moral actions.
Hume strongly opposes the idea that moral judgments are the conclusion of reason. The role of reason in relation to moral judgments is to be only in relation to the passions. Reason must be slave to man's passions. Reason is to help man find his moral obligations and duties, but reason does not produce or act on obligation or moral duty; man's passions motivate one to act.
Passion is the criterion for all moral judgments because there are no absolute moral values. Moral values differ from one person to the next because they are based on human experience.