The first part of part 2 of the Summa, consisting of 114 questions, offers an extensive discussion of man, who is said to have been made in God’s image. The first 5 questions, each of which is subdivided into various Articles, deal with man’s last end, the things in which man’s happiness consists, what happiness is, the things that are required for happiness, and the attainment of happiness.
First, in contrast to irrational animals, man has the faculty and will of reason. The will, also known as the rational appetite, seeks to achieve both its end and the good, and so all acts, being guided by the will, are for an end.
Second, man’s happiness does not consist of wealth, honor, fame, glory, power, the goods of the body, or pleasure. In fact, man’s happiness cannot consist in any created good at all, since the ultimate object of man’s will, the universal good, cannot be found in any creature but rather only in God, who is the source of all good.
Third, happiness is man’s supreme perfection, and each thing is perfect insofar as it is actual. Man’s final and complete happiness can consist only in contemplating the Divine Essence, although the possibility of this contemplation remains withheld from us until we are in the world to come. As long as man desires and seeks something, he remains unhappy. The intellect seeks the essence of a thing. For example, knowing an effect, such as a solar eclipse, the intellect is aroused and is unsatisfied until it discovers the cause of the eclipse. Indeed, the intellect desires to understand the essence of the cause. For this reason, the intellect is unsatisfied to know merely that the First Cause, that is, God, exists. The intellect seeks to penetrate farther to the very essence of the First Cause itself.
Fourth, the things required for happiness must derive from the way in which man is constituted and designed for a purpose, since happiness consists in man’s attainment of that final purpose. Perfect knowledge of the intelligible end, actual attainment of the end, and delight in the presence of the end attained must all coexist in happiness. Happiness in this life, which is necessarily imperfect, requires rectitude of the will, the existence of the body, and certain external goods and consists in the use of the intellect either speculatively or practically (i.e., with respect to morality). Perfect happiness, which is possible only in the life to come, consists in contemplation of the Divine Essence, which is goodness.
Finally, man is capable of attaining happiness, that is, of seeing God, and one person can be happier than another insofar as she is better inclined to enjoy him. Happiness excludes the presence of evil, though, and since evil is present in this world, it is impossible for man to be happy in this life. Furthermore, man cannot attain perfect happiness because he is incapable of seeing God in this life. Imperfect happiness can be lost, but perfect happiness cannot. Neither man nor any creature can attain final happiness through his natural powers. Since happiness is a good surpassing anything that has been created, no creature, even an angel, is capable of making man happy. Happiness is the reward for works of virtue. Some people do not know what happiness consists in and thus do not desire it.
The remaining questions of the first part of part 2 deal with a wide variety of issues related to the will, emotions and passions, virtues, sins, law, and grace. The second part of part 2, consisting of 189 questions, considers the “theological virtues,” such as faith, hope, charity, prudence, justice, fortitude, and temperance, and the gifts of grace, such as the power of prophecy, that some people possess. Finally, part 3, consisting of 90 questions, concerns a wide variety of issues related to Christ, such as his nature, his life, the Resurrection, the Sacraments, and penance. A supplemental set of 99 questions concerns a wide variety of loosely related issues such as excommunication, indulgences, confession, marriage, purgatory, and the relations of the saints toward the damned.
Happiness is the goal of human life, and every human being is on the path toward the complete actualization of his or her potential. Indeed, humans’ actualization and realization of their potential is exactly what constitutes happiness. Humans’ potential, or what humans can be, consists in the contemplation of the Divine Essence. Happiness and the contemplation of the Divine Essence are thus identical and inseparable.
The contemplation of the Divine Essence is not only necessary for happiness, it is uniquely sufficient. Nothing except the contemplation of the Divine Essence can bring happiness. No worldly or material good, such as fame, honor, glory, power, health, or even pleasure itself can bring happiness, as even pleasure is just a component of happiness. A state of happiness can exist only when the will no longer seeks anything. Since the will naturally seeks the Divine Essence, it will continue to seek, and thus to be unhappy, until it finds it.
Aquinas applies Aristotle’s notions of efficient and final cause here, whereby human nature, in the form of the will, is the efficient cause and happiness, or contemplation of the Divine Essence, is the final cause. The will thus inescapably propels every individual to seek happiness. The process of becoming leads naturally to God, who is pure being and actuality. The culmination of this process, though, is possible only in the next life and only works of virtue, that is, performance of the will of God, can lead to this culmination. Thus, the will achieves its goal, which is happiness, only when it is at one with the Divine Will.
The remainder of the Summa examines these various works of virtue, as well as sin, and explains the role of Christ, who mediates between God and man. The supplement to the Summa, which was added to the Summa after Aquinas’s death, discusses sundry related issues that Aquinas presumably might have incorporated into his great work had he lived to complete it.