Plato’s doctrine of cardinal virtues is based on his concept of virtue. According to Plato, goodness consists of the natural and proper functioning of human nature. Besides, man is social by nature; therefore, society is a normal background of moral life of human beings. Socrates had said that virtue is knowledge. It means that insight into the nature of moral virtues is essential for becoming virtuous. Of course mere knowledge of virtue is not enough. Man has to cultivate virtues through the habit of doing obligatory and morally good actions. For Plato, good life is the life of virtues.
Plato has described four important virtues in his theory of morality. According to him the cultivation of these four virtues – wisdom, courage, temperance, and justice – constitutes a morally good life. Later on, these four virtues came to be called ‘Cardinal virtues’. The term ‘cardinal’ is derived from the word ‘Cardo’ ‘Cardo’ means a hinge or a hook which supports the door, and on which the door turns. The four virtues are cardinal because they support moral life of man in society. They are fundamental virtues. Other virtues depend upon them and are therefore subordinate to them. Thus, cardinal virtues, according to Frankena, are a set of virtues which cannot be derived from one another; and all other moral virtues can be derived from them or shown to be forms of them.
These four virtues are said to be the basic and important constituents of moral life or goodness of man. Morality consists in knowing and maintaining the harmony between the rational and non-rational elements of the self.
Wisdom is the virtue of reason. It consists in knowing and mastering the non-rational elements viz. spirited element and passions. It includes knowledge, insight and foresight based on that knowledge. It is not bookish knowledge/data/information only. It implies the active choice of values as against disvalues, or virtues as against vices. A man is wise in whom reason rules over the other impulses.
Courage is the virtue of the spirited element. It must perform its heroic function within the limits set by reason. It is of two types viz. physical courage of a soldier and moral courage of a thinker or a reformer. Thus, one can be courageous in war as well as in intellectual convictions. Courage, therefore, is the excellence in the activity of the will. A man is brave when the spirited element holds fast to the instructions of intellect.
Temperance or self-control consists in keeping bodily satisfactions within limits. Passions are not to be condemned. Even they are to be satisfied. The passionate element is both non-moral and non-rational. It needs to be regulated and subjected to the rules of reason. Temperance is not complete abstinence. It is the principle of self-restraint and moderation. It is the controlling and ordering of natural instincts, desires and sensuous pleasures. A man is temperate when the spirited element or passionate element yields to intellect and obey its commands.
Justice is the virtue of the whole self or the complete person. It is the proper integration of different parts of the self. Thus, justice also consists of the harmonious functioning of the three parts of personality. Each part must do its function for which it is fit. When these three parts of the personality or the self with their three virtues of wisdom, courage and temperance function harmoniously together and are ordered and ruled by reason, then justice emerges as the resultant virtue. Each man is fit for a particular job in accordance with his nature. Justice consists in doing one’s own job. Being morally perfect, therefore, is tantamount to being wise, valiant, temperate and just. Justice, then, is the supreme virtue. Just man will not indulge in the pursuit of material pleasures only.
According to Plato, the four cardinal virtues have both individual and social significance. They are found both in the individual and in society. Human beings are rational and social animals. They have the natural tendency to live in communities. The morality of society is the same as it is for the individual. According to Plato, society is the individual ‘writ large’. For society is made up of individuals.