This renowned treatise on ethics was highly influential in ethical theory in Sidgwick's time. After discussing the history of ethics in full, he goes on to outline his theory—that there are three methods of ethics: egoistic hedonism (what will ultimately be best for one), intuitionism (what an immediate sense morality tells one to do), and utilitarianism (what will be best for everyone). Sidgwick determines how these thoughts work together.