Aquinas viewed theology, or the
sacred doctrine, as a science, the raw material data of which consists of written scripture and the tradition of the Catholic Church. These sources of data were produced by the self-revelation of God to individuals and groups of people throughout history. Faith and reason, while distinct but related, are the two primary tools for processing the data of theology. Aquinas believed both were necessary ... or, rather, that the
confluence of both was necessary ... for one to obtain true knowledge of God. Aquinas blended Greek philosophy and Christian doctrine by suggesting that rational thinking and the study of nature, like revelation, were valid ways to understand truths pertaining to God. According to Aquinas, God reveals himself through nature, so to study nature is to study God. The ultimate goals of theology, in Aquinas’ mind, are to use reason to grasp the truth about God and to experience salvation through that truth.
Nature of God
Aquinas believed that the existence of God is neither obvious nor unprovable. In the
Summa Theologica, he considered in great detail five reasons for the existence of God. These are widely known as the
quinque viae, or the "Five Ways."
Concerning the nature of God, Aquinas felt the best approach, commonly called the
via negativa, is to consider what God is not. This led him to propose five statements about the divine qualities:
- God is simple, without composition of parts, such as body and soul, or matter and form.
- God is perfect, lacking nothing. That is, God is distinguished from other beings on account of God's complete actuality.
- God is infinite. That is, God is not finite in the ways that created beings are physically, intellectually, and emotionally limited. This infinity is to be distinguished from infinity of size and infinity of number.
- God is immutable, incapable of change on the levels of God's essence and character.
- God is one, without diversification within God's self. The unity of God is such that God's essence is the same as God's existence. In Aquinas's words, "in itself the proposition 'God exists' is necessarily true, for in it subject and predicate are the same."
In this approach, he is following, among others, the Jewish philosopher Maimonides.
Following St. Augustine of Hippo, Aquinas defines sin as "a word, deed, or desire, contrary to the eternal law." In other words, anything that disobeys God's will is said to be a sin, and is synonymous with "evil" (privation of good, or
privatio boni).
Nature of the Trinity
Aquinas argued that God, while perfectly united, also is perfectly described by Three Interrelated Persons. These three persons (Father, Son, and Holy Spirit) are constituted by their relations within the essence of God. The Father generates the Son (or the Word) by the relation of self-awareness. This eternal generation then produces an eternal Spirit "who enjoys the divine nature as the Love of God, the Love of the Father for the Word."
This Trinity exists independently from the world. It transcends the created world, but the Trinity also decided to communicate God's self and God's goodness to human beings. This takes place through the Incarnation of the Word in the person of Jesus Christ and through the indwelling of the Holy Spirit (indeed, the very essence of the Trinity itself) within those who have experienced salvation by God.
Prima Causa - First Cause
Aquinas' five proofs for the existence of God take some of Aristotle's assertions concerning principles of being. For Aquinas, God as Prima Causa (first cause) comes from Aristotle's concept of the Unmoved Mover and asserts that God is the ultimate cause of all things.
Nature of Jesus Christ
In the
Summa Theologica, Aquinas begins his discussion of Jesus Christ by recounting the biblical story of Adam and Eve and by describing the negative effects of original sin. The purpose of Christ's Incarnation was to restore human nature by removing "the contamination of sin", which humans cannot do by themselves. "Divine Wisdom judged it fitting that God should become man, so that thus one and the same person would be able both to restore man and to offer satisfaction." Aquinas argued in favor of the satisfaction view of atonement; that is, that Jesus Christ died "to satisfy for the whole human race, which was sentenced to die on account of sin."
Aquinas argued against several specific contemporary and historical theologians who held differing views about Christ. In response to Photinus, Aquinas stated that Jesus was truly divine and not simply a human being. Against Nestorius, who suggested that Son of God was merely conjoined to the man Christ, Aquinas argued that the fullness of God was an integral part of Christ's existence. However, countering Apollinaris' views, Aquinas held that Christ had a truly human (rational) soul, as well. This produced a duality of natures in Christ. Aquinas argued against Eutyches that this duality persisted after the Incarnation. Aquinas stated that these two natures existed simultaneously yet distinguishably in one real human body, unlike the teachings of Manichaeus and Valentinus.
In short, "Christ had a
real body of the same nature of ours, a
true rational soul, and, together with these,
perfect Deity." Thus, there is both unity (in his one
hypostasis) and diversity (in his two natures, human and Divine) in Christ.
Echoing Athanasius of Alexandria, he said that "The only begotten Son of God...assumed our nature, so that he, made man, might make men gods."
Goal of human life
In Aquinas's thought, the goal of human existence is union and eternal fellowship with God. Specifically, this goal is achieved through the beatific vision, an event in which a person experiences perfect, unending happiness by seeing the very essence of God. This vision, which occurs after death, is a gift from God given to those who have experienced salvation and redemption through Christ while living on earth.
This ultimate goal carries implications for one's present life on earth. Aquinas stated that an individual's will must be ordered toward right things, such as charity, peace, and holiness. He sees this as the way to happiness. Aquinas orders his treatment of the moral life around the idea of happiness. The relationship between will and goal is antecedent in nature "because rectitude of the will consists in being duly ordered to the last end [that is, the beatific vision]." Those who truly seek to understand and see God will necessarily love what God loves. Such love requires morality and bears fruit in everyday human choices.
Treatment of heretics
Thomas Aquinas belonged to the
Ordo Praedicatorum (commonly known as the Dominicans), whose primary goal is the peaceful conversion of the Albigensian heretics. In the
Summa Theologica, he wrote:
With regard to heretics two points must be observed: one, on their own side; the other, on the side of the Church. On their own side there is the sin, whereby they deserve not only to be separated from the Church by excommunication, but also to be severed from the world by death. For it is a much graver matter to corrupt the faith which quickens the soul, than to forge money, which supports temporal life. Wherefore if forgers of money and other evil-doers are forthwith condemned to death by the secular authority, much more reason is there for heretics, as soon as they are convicted of heresy, to be not only excommunicated but even put to death.
On the part of the Church, however, there is mercy which looks to the conversion of the wanderer, wherefore she condemns not at once, but "after the first and second admonition," as the Apostle directs: after that, if he is yet stubborn, the Church no longer hoping for his conversion, looks to the salvation of others, by excommunicating him and separating him from the Church, and furthermore delivers him to the secular tribunal... ( Summa, II-II, Q.11, art.3.)
Heresy was against the secular law in most European countries of the 13th century. Aquinas' suggestion specifically demands that heretics be handed to a "secular tribunal" rather than magisterial authority. That Aquinas specifically says that heretics "deserve... death" is concerning his theology, where all sinners do not deserve life ("For the wages of sin is death; but the free gift of God is eternal life in Christ Jesus our Lord"). He elaborates on his opinion regarding heresy in the next article, when he says:
In God's tribunal, those who return are always received, because God is a searcher of hearts, and knows those who return in sincerity. But the Church cannot imitate God in this, for she presumes that those who relapse after being once received, are not sincere in their return; hence she does not debar them from the way of salvation, but neither does she protect them from the sentence of death. ( Summa, op. cit., art.4.)