The idea of virtue and its role in ethical behavior comes from Greek philosophy. Plato, who lived in the fourth century B.C., identified four virtues that have become influential concepts in Western civilization. Now known as the four cardinal virtues, they are wisdom, courage, moderation and justice. He wrote about these virtues in the "Republic," a Socratic dialogue on political theory. Other philosophers have argued that the four virtues provide the basis for all aspects of moral character. Aristotle, a student of Plato, expanded the concept by including additional virtues, as did Christian theologians.

Wisdom

Wisdom, or prudence, is the capacity to make sensible decisions and judgments based on personal knowledge or experience. It is the ability to recognize, differentiate and choose between right and wrong. It is deemed the most essential of the four virtues. Plato considered wisdom the virtue of reason and believed that being truly virtuous is possible only when one acts on reason. In ancient Greek philosophy, wisdom is regarded as the virtue of rulers, since it enables rulers to take advice and then act prudently, based on their own reason.

Courage

Courage, or fortitude, is the ability to confront fear, intimidation, danger, difficulty and uncertainty. It is the ability to face a challenge without cowardice. In ancient Greece, courage was regarded as a military virtue, a character trait of soldiers waging war on the battlefield. Both Plato and Aristotle held military excellence in the utmost regard. The soldier was the Greek model for courage and heroism.

Moderation

Moderation, or temperance, is the quality of practicing self-restraint and self-control. Plato thought that controlling the appetite, instead of being driven by reckless desires, was an indispensable virtue. He wrote another Socratic dialogue, Charmides, on the virtue of temperance. Since the time of Plato, temperance has been associated with abstinence and sobriety.

Justice

The bond that unites the other three virtues is justice. Justice is the quality of being fair and reasonable, particularly in how decisions are made and the way people are treated. Plato believed that a person would become just after having achieved the other three virtues. He emphasized the interconnectedness of the four virtues, stating that the human soul is perfect when all of those parts are present and functioning. He believed that society is ordered through justice, but this can be attained only when the human soul is well ordered. According to Plato, only just people can create a just society.