Moral philosophy has three branches: ethical, domestic, and political (In NE I.1.6). What we should and should not do is ultimately determined with reference to the chief human good (ST Ia. IIae.1.6), which we have seen is happiness (ST Ia.82.1c). Following Aristotle, Aquinas accepts that what functions well is good, and thus a human who functions well will be a good human, or a human who has acquired the human good. The human good is happiness, so a human who functions well will be happy (In NE I.10.128). That human beings have a function, Aquinas accepts on several grounds, including the belief that it would be absurd to suppose something ordained by divine intelligence should lack a purpose (In NE I.10.121). Our function is what makes us unique vis-ii-vis other animals, namely our rationality (In NE I.10.126). To function well requires possession of the appropriate virtue; thus, the virtue of a knife is sharpness as the function of the knife is to cut. Hence successful moral reasoning involves several factors; since the intellect is divided in terms of practical and speculative applications, to which there correspond various intellectual virtues. However, we have seen that human beings are likewise motivated by intellectual and sensitive appetitive faculties, whose proper functioning requires moral virtues, whose role is to ensure that what we desire is conducive to our overall good. The moral virtues depend on reason if they are to show themselves in activity conducive to our well-being, for without the intellectual virtues of prudence (which grasps means to ends), and understanding (which supplies the deliberations of prudence with the requisite first principles) (among other places, see In NE VI), the mere possession of appropriate desire would be insufficient to ensure our welfare (ST Ia. IIae.58.4, ad 3). Thus the activity of the appetitive faculties that these virtues perfect may be termed rational in a broader sense, inasmuch as they can obey the regulation of reason in the manner a child obeys her parents or a youth the counsel of wise friends (In NE I.20.240). Conversely, as prudence is right reason about what should be done, it depends on the rectitude of our appetites as concerns the desired end, and thus prudence (a virtue of the practical intellect) depends on the moral virtues, which dispose us toward the proper end (ST Ia. IIae.57.4c). Morality consequently supposes the exercise of deliberation and volition in accord with the intellectual and moral virtues, respectively.
While it is true that happiness is man’s chief end, our ultimate happiness is not found in this life. Rather the greatest human happiness will come only in the beatific vision, ‘‘for man and other rational creatures attain to their last end by knowing and loving God’’ (ST Ia. IIae.8.2c) (cf., ST Ia. IIae.3.8c). Attainment of our ultimate end requires the supernatural virtues of faith, hope, and charity, which are acquired through grace (ST IIa. IIae.1-46). Nonetheless, Aquinas believes that our lives on earth afford a measure of happiness; indeed, our inclination to pursue that happiness serves as the first principle of morality underpinning God’s natural law. Natural law is the eternal law ruling creation as subject to God’s providence, imprinted on creatures in the form of proper inclinations (ST Ia. IIae.91.2c). The first precept of natural law is that we should seek good and shun evil, the moral equivalent of the principle of noncontradiction (ST Ia. IIae.94.2c). What humans pursue and avoid is determined by their nature as rational, animate substances, which, among other things, inclines them to preserve their own being, mate and raise offspring, and live together in peaceable society. To the extent we are aware of and follow these desires in an appropriate manner, we follow natural law, and this brings us happiness.
World History
