It would appear, then, that the four traditional virtues of wisdom, justice, courage and temperance may be defended as cardinal in terms of the four theses stated earlier in this paper. They are cardinal in so far as they do not appear to be mutually reducible, reference to each of them is indispensable for a full account of moral virtue and they represent the four main types of virtue of which all other particular non-cardinal virtues may be considered tokens (although any particular virtue may, as Plato might have said, partake of the forms of one or more of the four main types; chastity, for example, may be some sort of mixture with respect to sexual life of wisdom, justice and temperance). Finally, there are just four cardinal virtues, no more or less, because between them they would appear to safeguard human nature in all of the areas in which moral failure or error may occur in human affairs; harmful or excessive indulgence in sensual pleasure, misconduct under the influence of emotion or passion, unjust treatment of others through self-love or pride and careless or foolish conduct following from ignorance or a defect of wisdom.
David Carr, "The Cardinal Virtues and Plato's Moral Psychology", The Philosophical Quarterly, Vol. 38, No. 151 (Apr., 1988), p. 200.
