Nicomachean Ethics
Discussion of what were known as the Four Cardinal Virtues—wisdom, justice, fortitude, and temperance—can be found in Plato's "Republic". The virtues also figure prominently in Aristotle's moral theory found in Nicomachean Ethics. Virtue theory was inserted into the study of history by moralistic historians such as Livy, Plutarch, and Tacitus. The Greek idea of the virtues was passed on in Roman philosophy through Cicero and later incorporated into Christian moral theology by St. Ambrose of Milan. During the scholastic period, the most comprehensive consideration of the virtues from a theological perspective was provided by St. Thomas Aquinas in his "Summa Theologiae" and his "Commentaries on the Nicomachean Ethics". After the Reformation, Aristotle's Nicomachean Ethics continued to be the main authority for the discipline of ethics at Protestant universities until the late seventeenth century, with over fifty Protestant commentaries published on the Nicomachean Ethics before 1682.