Like Aristotle's ethics, the ethics of Thomas Aquinas are teleological. This means he believed that a good life is directed toward some “end” or goal. But for Aquinas the proper end of human activity is different than for Aristotle.
In his Nicomachean Ethics Aristotle argued that happiness (the Greek word is eudemonia, meaning something like “a good spirit”) is an “activity of soul in accordance with virtue.” Happiness is the proper end for all men, though people have also disagreed over what that happiness was. Some said it was honor, others said it was pleasure. Aristotle said it was neither, since the former is ephemeral and the latter depends upon the opinions of others. Two characteristics of happiness, he continued, must be its being “final” and “self-sufficient.” In other words, happiness needs nothing further to complete it. Surely external goods like wealth, having friends, and even good looks help in its attainment.
But a funny thing happened in Book X of his Nichomachean Ethics. For nine books “the Philosopher” (as Aquinas called him) said happiness was man's proper end and virtue the only means to that end. In Book X, however, he says that theoria (or contemplation), and not virtue, is man's greatest activity, since contemplation is what is “highest” in us. He meant that the activity of contemplation is most godlike. And what is God thinking of? God never fixes on the mundane events of this world but is contemplating metaphysics, mathematics, and other theoretical sciences. In Aristotle's haunting phrase, “God is thinking about his own thinking.”
The Virtues and the Ultimate End
Aquinas agreed with Aristotle that good human activity must pursue some purpose. As Aristotle spoke of virtues, so Aquinas addressed the cardinal (or “hinge”) virtues. These are prudence, justice, temperance, and courage. Since the human will requires rational direction to overcome appetites and anger, persons will need to cultivate virtues. The developmentof these virtues — which are habits — is necessary to achieving human fulfillment. But Aquinas thinks that by themselves they are not enough. This is even true of contemplation, which is the highest activity of theoretical reason, according to Aquinas.
Aquinas distinguished between an imperfect happiness achievable in this life and the perfect happiness of the next life. He thought that our ultimate end is eternal blessedness, which results from a union with God in the next life. If the purpose of life is the possession of the supreme good, the sonnum bonum, this cannot be found in the natural world, which is temporal and not eternal. Moreover, happiness is not found in mere knowledge about God but in acquaintance with him, achieved in the vision of the divine essence. Since knowledge of God attainable in this life is always imperfect, the natural desire of humans for ultimate fulfillment points to the necessity of an afterlife.
In fact, Aquinas insisted that Aristotle was at least vaguely aware of the imperfect happiness of this life. Aquinas cites a passage in Book I of the Nichomachean Ethics where Aristotle writes, “We shall define as ‘supremely happy' those living men who fulfill and continue to fulfill these requirements (namely possessing complete virtue), but blissful only as human beings.” Because Aquinas believed that Aristotle understood that the happiness achievable in this life is imperfect, he had no quarrel with Aristotle.