In The Mind of Thomas Aquinas

Thomas Aquinas, one of the most influential theologians of his time, deals with many hotly contested topics regarding the nature of God and God's dealings with mankind in Summa Theologica. In the fifth question of Part IIIa, Aquinas discusses Christ’s assumption of a human nature. Although most Christians believe that Jesus became a man in a general sense, the concepts of assumption and of human nature are often poorly understood. The simple phrase “Christ’s assumption of human nature,” then, warrants a thorough explanation. Because of this, Aquinas systematically responds to and rejects many of the objections of his contemporaries. Through his adherence to logical thought and precision of language, Aquinas disproves the claim that Christ did not assume a human mind, asserting instead that the assumption of a human mind was necessary for salvation to occur.

Aquinas believes that definitions are integral to the understanding of theological principles, and the structure of his arguments reflect this belief. He devotes much of his writing to defining terms so that his audience has an accurate understanding of important concepts. Christ’s assumption is no exception. Throughout his discussion, Aquinas reveals the definition of assumption. He says that it is impossible to “assume a body to the unity of the nature” and cites Augustine’s assertion that in the assumption, Christ maintained the fullness of his divinity (S.T. 3a, q. 5, a. 1, ad. 2). Aquinas believes that assumption is not a mixing of two natures; rather, the natures of Christ and man remain distinct. For Aquinas, assumption is the act of taking on another nature that is maintained in its entirety but still remains secondary to the original nature of the Person. Regarding the human nature of Christ, Aquinas comes to the conclusion that human nature consists of two facets: the body and the soul (3a, q. 5, a. 3, co. 1). One aspect of the soul is the mind, which enables man to reason and make decisions (3a, q. 5, a. 4, ad. 3). Using these definitions, Aquinas responds to the claim that Christ did not assume a human mind, and subsequently did not fully assume human nature.

In the discussion preceding the current topic, Aquinas comes to three major conclusions: that Jesus assumed a real body, that Christ’s human body was a physical one, and that Christ also assumed a human soul (3a, q. 5, a. 1-3). In this section, he focuses on the soul and considers whether Christ assumed a complete human soul or whether he omitted the human intellect. The major opposition to the idea of Jesus assuming a human mind is that Christ, with the wisdom of God, did not need a human mind (3a, q. 5, a. 4, arg. 1). God is omniscient, and as a result, so too is Jesus. For Aquinas’ opponents, it is logical that Christ assumed a human body, because God does not have a physical form. It does not make sense to them, though, that Christ would assume a finite mind with limited capacity when he already knows everything. In his response to this argument, Aquinas gives three reasons why it is not only logical but imperative that Christ assumed a human mind.

The simplest reason why Aquinas believes that Christ assumed a human soul in its entirety is because the Bible implies it. Throughout the Gospels, many of Jesus’ actions are indicative of a human intellect. Luke states that “Jesus increased in wisdom and stature,” but an all-knowing God cannot become more wise (Holy Bible, Luke 2:52). Aquinas cites a similar instance as evidence that Christ must have a human intellect. Matthew states that Christ marveled at the faith of the Roman officer (Matthew 8:10). Christ, in this encounter, “see[s] an effect and [is] ignorant of its cause,” and this leads him to marvel (S.T. 3a, q. 5, a. 4, arg. 1). The divine nature of Christ cannot account for this response: Christ, in his divinity, would know why the Roman officer had so much faith and what caused him to express it in that moment. The only way that Christ would have the ability to marvel is if he has a finite mind, which suggests that he assumed one when he came to earth.

Aquinas also rejects the idea of a Christ without a human intellect because it is contrary to the truth of the Incarnation (3a, q. 5, a. 4, arg. 1). The word “incarnation” describes the process of going into the flesh. Flesh does not reference only the body, but “the whole man is signified by flesh” (3a, q. 5, a. 3, ad. 1). In this synecdoche, flesh is used to refer to all of a human’s nature, both the soul and the body. Based on this understanding, one cannot not have true flesh unless one has both a body and a soul. As stated in the Gospel of John, Christ became human flesh, so by definition, he assumed a human body and a human soul (John 1:14). Aquinas claims that the aspect of man’s soul that makes it distinctly human is its rationality, “since our soul differs from an animal soul by the mind alone” (3a, q. 5, a. 4, arg. 1). Because the mind is the distinguishing factor of the human soul, it was necessary that Christ assume a mind in his assumption of human nature. Without one, Jesus would not be “in the flesh” of a human and the Incarnation would cease to be true.

The claim that Christ assumed a human mind is not only evidenced in the Bible by reference to the Incarnation, but is one of the reasons why the Incarnation occurred. For Aquinas, the purpose of the Incarnation was “justification of man from sin” (3a, q. 5, a. 4, arg. 1). Aquinas also cites Damascene, saying that “what was not assumed is not curable” (3a, q. 5, a. 4, arg. 1). Jesus took on a human nature so that he could live a sinless life and die for the sins performed by mankind while in the flesh. Christ’s righteousness in the different aspects of human nature, then, cover the sins done with those faculties. Aquinas says that “the human soul is not capable of sin…except through the mind” (3a, q. 5, a. 4, arg. 1). From this statement, it is apparent that Aquinas believes that the human soul is not inherently sinful; the human soul sins because the mind enables it to sin. The mind houses man’s ability to reason and exercise free will, and through this free will, one is able to choose to sin. Those that argue that Jesus did not assume a human mind are suggesting that the human mind was not justified in Christ’s death. If this is true, then it would mean that the aspect of the soul that supplies the free will to sin was not made righteous through Christ. The mind would not be covered by the grace of God, and would be judged according the standards of holiness set by God. Because man’s mind is imperfect, he would be condemned. Thus, mankind would still be separated from God by sin, and the purpose of the Incarnation would not be fulfilled. Aquinas rejects this claim, though, because it is inconsistent with his understanding of the Incarnation.

This discussion of whether Jesus assumed a human mind is a part of the greater discussion of human nature, the Incarnation, and the act of salvation. Aquinas thinks of the Bible not as the sole source of knowledge about God, but as the foundation for his theological discussions. He uses the Bible to ground the arguments that can be further developed using reason. Specifically in this passage of Summa Theologica, Aquinas argues for Christ’s assumption of true human nature while implicitly asserting the inherent goodness of human nature as God created it. Furthermore, in demonstrating that Christ did have a human mind, Aquinas validates the theological work he is doing. If Christ used his human mind to fulfill the will of the Father, so too can theologians, empowered by the Holy Spirit and covered by God’s grace, use their minds to give glory to God. In this way, Aquinas contributes to the better understanding of God, his nature, and how he relates to mankind.