Ethical principles are not mechanical rules that can be used as a substitute for thought. Rather, each principle conveys an understanding of some aspect of reality and must be intelligently applied to every practical situation. An especially important category of ethical principles are the virtues—that is, the fundamental character traits, manifested in one's actions, that a person needs to develop over a period of time. Like all ethical principles, each virtue (as we shall show) serves in practical ways to maintain and improve a person's life, both in terms of one's inner psychological integration and in one's relationship to physical reality and other beings.

The science of ethics is needed both by the individual in isolation and by individuals acting in a social context. Our observations on social ethics (near the end of Section 3) will later become essential to our analysis of the dynamics of social/political systems.