This article explains how Aquinas analyzes human nature through the relationship between philosophy and theology, exploring how human beings, as social and political beings, form communities and nations.

Attempts to analyze human beings have been made in a variety of ways, both ancient and modern. Plato attempted to analyze human nature in his Politics, where he studied the principles of the state and politics. In the Renaissance, Machiavelli also analyzed human nature in The Prince, explaining the most human act of all, politics. One of the most interesting of these attempts is that of Aquinas, who analyzed human nature from a religious perspective. Aquinas specifically analyzed human beings in his Summa Theologiae. The first part of the Summa Theologica deals with the nature and attributes of God, the trinity of divine persons, and creation, while the second part describes and analyzes man as a moral agent. In the relationship between God and man, Aquinas attempts to analyze human nature through analogy.

Aquinas’s Logical Analysis of Man

Before we look at Aquinas’s view of human nature, it’s important to understand how he understood theology and philosophy. The medieval period in which Aquinas was active can be summarized by the phrase “philosophy is the handmaiden of theology” (ancilla theologiae). Aquinas’s position on philosophy and theology can be seen in a passage from his Summa Theologiae.
“Natural reason must assist faith because grace does not destroy nature, but rather perfects it. It is as if the natural tendency of the will must obey love.”
As this sentence shows, philosophical truth and theological truth are complementary. Philosophical truth on its own provides only incomplete truth and must be supplemented and completed by theological truth, which is the ultimate truth. On the other hand, theological truth is not separate from nature (philosophical truth). Since theological truth is revealed in nature in the form of revelation, it cannot be completed without nature (philosophical reflection). An academic analysis of the relationship between philosophy and theology can be summarized in three ways. First, faith revealed by natural reason (philosophy) and faith guided by the power of faith are complementary and harmonious. Second, just as grace is manifested in the natural world in the form of images, so theological truth presupposes natural knowledge. Third, grace (theology) does not destroy nature (philosophy), but rather completes it.
Aquinas’s favorable attitude toward philosophy is due to the fact that he was strongly influenced by Aristotle. Aristotle’s philosophy is based on two principles: reason and experience. Aristotle’s successful application of these two seemingly irreconcilable elements to reality made his philosophy suitable for harmoniously combining the two disparate disciplines of theology and philosophy. Aquinas took it a step further by arguing against the limitations of naturalistic philosophy, such as the eternity of the world and the separation of active reason, from a religious perspective. In other words, he used the logic of religion to overcome what he saw as the limitations of Aristotelian philosophy.
Aquinas borrows from Aristotle’s work in identifying the essential structure of human beings. He divides the soul, the substantial form of man, into intellect and appetite, which he further subdivides into active and passive intellect, speculative intellect, and practical intellect. The appetites are further analyzed by dividing them into natural, intellectual, and sensual needs. This analytical framework is quite similar to Aristotle’s, where Aquinas describes the unique position of human beings in the hierarchy of all beings, including animals and plants, by grading them according to their mental levels. Furthermore, humans are created in the image of God and are guaranteed the most special status of all beings. Aquinas then analyzes how humans live in community in society.
Specifically, Aquinas’s position on the analysis of human beings is as follows Beings are divided into material and immaterial beings. Material beings are the animals, plants, etc. that we can identify in the natural world, while immaterial beings are called “separate entities,” such as angels and the Holy Spirit. Aquinas argues that humans have the unusual property of belonging to both material and immaterial beings. This is due to the nature of the human soul, which is the primum principium vitae of living creatures and necessarily accompanies life. At the same time, the soul can stand on its own, independent of the body. However, this is not a dichotomous discussion that presupposes the separation of the soul from human existence. The soul’s ability to be self-sustaining means that it can recognize all material things. This ensures the soul’s unique status and ties in with Aquinas’ intention to pinpoint the principle of the essence of objects.
Aquinas identifies grades of souls, and this hierarchy represents an order of being. At the apex of this hierarchy is God, who is pure reality. God is a mental being in the most exceptional sense, characterized by simplicity. God is an infinite and complete being, and as a creature, man cannot perceive God univocally or aequivocally, but only analogically. All beings, except God, have a distinction between essence and existence, between essence and acts, between acts themselves and each other, and between the capacity to understand and the capacity to desire. The highest of beings other than God are the angels, who are not united in substance and form. Angels are more perfect than men, and more like God than men. Other than gods and angels, other beings include human, animal, and plant spirits. The plant soul is the first principle in the growth of life, and the animal soul is not only the first principle of life but also the first principle of sensation. The human soul contains the life-growth principle, the sensory principle, and the rational principle. These divisions represent a hierarchy of souls, divided into inferior and superior.
The most unique characteristic of the human soul is that it has a rational principle. Specifically, the rational principle is divided into intellect and desire. Knowledge by the intellect is the acceptance of the form of an object. Aquinas says that an understanding of the structure of human nature is an understanding of the human soul. Since the human soul is the principle of reason, an understanding of the intellect and appetites is an understanding of the human person.
The intellect is divided into active and passive intellect. The function of the active intellect is to apprehend existence, i.e., the human soul is a blank slate until the active intellect acts to understand it. Along with perception, there are the senses to consider. We perceive things through our sensory organs, and the intellect takes in the perceived things through the senses to form individual sensory images. What’s unique about the human perception process is that external objects are not reproduced through the senses, but rather imprinted. For example, even in the process of recognizing inanimate objects such as a chair or bed, the object is not a passive entity, but an entity that can imprint certain impressions on the human being. Scholars of the Summa Theologiae describe the process of human cognition as “knowing the nature of things” as described by Aquinas. The final step in the cognitive process is judgment, where we recognize the existence of an object through judgment. In other words, the cognitive process can be divided into ‘perception’ and ‘judgment’. Mere perception is not enough to make a judgment about right and wrong.
Aquinas’s epistemology can be summarized as an exploration of the subject and object of cognition and the ancient tradition of sensory and intellectual cognition. Thomas Aquinas lived in the Middle Ages, a period dominated by a Christian worldview. To understand Aquinas’s epistemological thought, we need to accept a certain amount of religious thinking.
First, Aquinas identifies the subject of cognition as a human being. This is a new way of looking at humanity, not as a species, but as a union of soul and body. Man is a unity of soul and body. What’s important to note is that Aquinas approaches the mechanism of cognition in two dimensions: body and soul. Second, Aquinas divides the objects of cognition into two categories: sensory cognition and intellectual cognition. The objects of sensory perception are material things, while the objects of intellectual perception are the essence of things. When Aquinas divides cognition into sensory and intellectual, he is not arguing that there are different cognitions of the same order, but rather that there are stages of cognition: humans, as a unity of spirit and body, use sensory experience as the first ground of cognition. Aquinas divides the senses into two categories: external and internal. The external senses are touch, sight, smell, taste, and hearing. The characteristic of the external senses is that they are very passive in the process of perception. The role of the external senses is to take in the appearance of external objects as they are. In addition to the external senses, humans have a unique ability called internal sensation, which is the ability that humans share with objects, through which sensory images are formed.
Next is intellectual perception. This is the process by which the sensory perceptions are transformed into the essence of the object. Aquinas distinguishes intellectual perception between the passive and active intellect. The function of the passive intellect is to turn sense images into objects that can be thought of realistically through abstractions. And the active intellect abstracts the images from the sensory images and imprints them on the passive intellect, so that the human intellect grasps the form of things; that is, through the active intellect, the sensory images become impressions, and through the passive intellect, the impressions are formed in the interior of the soul and formed into knowledge.
Aquinas’s epistemology is significant because it specifically describes the formation of perception and intellect. Rather than being revolutionary, Aquinas’s findings can be seen as an adaptation of Plato’s position in that he divided cognition into two layers: sensory cognition and intellectual cognition. Instead, through a specific description of the internal and external sense organs, he further explains the process by which external objects are formed into sensory images and the process by which sensory images are formed into forms and received as knowledge.
Next, he examines the characteristics of human beings as the “image of God. According to Aquinas, human nature is formed according to the image of God. God is the root cause of all existence. Human beings are created in the image of God. It’s important to note that being created in the image of God does not mean being “like” God, but rather being similar to some aspect of God. For humans, the image of God has three stages. First, humans are predisposed to understand and love God. This is common to all humans and is a reflection of the Christian worldview. For example, humans are supposed to have a love for God, which clearly distinguishes the ontological position of people of faith from people without faith. Second, humans recognize and love God imperfectly through their own power alone. To perfect this, they need the power of faith, which is grace and salvation. Third, humans have the capacity to know and love God perfectly, and to love God in a perfect way is called the “image of glory. In addition to these three abstract concepts, humans have the highest hierarchy of all beings except God and angels. This is because humans, like gods, can perform the function of perception. The ability to recognize, which is not found in animals, plants, or objects, is unique to God and humans, according to Aquinas.
Before we turn to Aquinas’ social (political) theory, it is important to note that he distinguishes between human actions and human acts. “Human acts” are those that are performed by the intellect and will. ‘Human acts’ refer to all activities other than human acts.

Aquinas’s logical analysis of society (politics)

Aquinas’ theory of society (politics) is quite similar to Aristotle’s, but in some ways it is a developmental continuation. Aquinas develops his social theory by accepting Aristotle’s proposition that man is a social animal. Aquinas holds a teleological view of existence, meaning that all creatures are born with an inherent purpose. Some beings inevitably fulfill their purpose. But humans cannot fulfill their purpose alone. Humans are inherently social and political beings and cannot fulfill their purpose alone. In addition to our communal nature, we also have needs. These needs are what drive us to pursue our purpose. According to Aquinas, the universal nature of human beings is such that they desire and long to achieve the common good while pursuing their personal good. The common good requires a group, and a group inevitably needs a leader to guide it. Groups and leaders are essential to beings seeking the common good.
In theology, the legitimacy of a leader is determined by the authority to rule. The right to rule is necessary for the pursuit of the common good, but its legitimacy is granted by God; that is, the nature to seek the common good is itself implanted in humans by God’s will, so the legitimacy of the leader to guide it comes from God. Since the right to govern is divinely derived, the community of the state is also created by the divine will and fulfills a divinely assigned function.
To understand Aquinas’ view of the state, we need to understand Augustine’s view of the state. According to Augustine, the state is the result of human beings being born with original sin, and without divine rule, the state is a collection of corruption. Fallen humans have lost their true God-given freedom, and Augustine distinguishes between freedom and self-indulgence. In a fallen state, humans are in a state of self-indulgence, and the state needs coercive sanctions to cleanse them.
Aquinas uncritically accepts both Aristotle’s and Augustine’s theories of the state: he accepts Aristotle’s human sociality and Augustine’s justification of the state. For Aquinas, the justification of the state means that the state is not simply a collection of indulgent human beings, but an a priori concept created by human nature that seeks to realize the true good. Unlike Augustine, however, Aquinas argues that the state is not the result of the fall of man, but rather that even before original sin, humans were organized into societies and pursued the common good, and had leaders or communities to guide them. According to Aquinas, the state is a complete society. Within the state, its members are free to use any means to achieve the common good. The legitimacy of the ruling power is enacted in the direction of fulfilling the common good. Military force and the judicial system are the means to remove any obstacles that might harm the common good. However, these sanctions must not infringe upon the human mind. The mental activity of man is directly related to God, and therefore, even if the rule of the state is legitimized by God, it must remain a private matter, for the spiritual ends of man can only be fulfilled by God. It is the church, not the state, that can guide mental activity, and according to Aquinas, the church is a higher concept of society than the state. However, the hierarchy of state and church does not require direct interference with each other. The state and the church do not interfere with each other because of their different contributions to the community. However, he argues that the king should be subservient to the clergy because the king oversees earthly matters, while the clergy oversees transcendent purposes.