St. Thomas Aquinas’s Philosophy and Theology
St. Thomas Aquinas’s Philosophy
Ontology
St. Thomas Aquinas, in his conception of reality, largely adopted Aristotle’s theories (teleology, the four causes of movement, hylomorphism, substance, act and potency, and accident). However, he also integrated Christian concepts, establishing a distinction between human understanding and divine revelation. The belief in God as the creator of the world implies a radical difference between God and other beings created by Him. Created beings might not have existed; their existence is contingent, not necessary. Contingency characterizes all that can exist or not exist. In contrast to contingent beings is God, who is necessary—He necessarily exists (cannot not exist) and is the principle and cause of all other beings.
Aquinas distinguished two aspects of all reality: the essence of beings (their universal definition, what they are) and their existence (the fact that they exist). Contingent beings are composed of essence and existence, as their essence does not necessarily imply their existence. Only in the necessary being, God, are essence and existence identical; His essence implies His existence.
The essence is the potency of being (it determines the capacity or potential to be), and existence is the act of being (it actualizes the potential to be of an essence). Each essence corresponds to a particular type of existence (a different way of being). There are degrees of perfection in beings, and therefore, some beings are more perfect than others because their essences have more potency to be. Aquinas posits a hierarchical organization of beings based on their likeness to the first cause of existence (God) or, in other words, their participation in divine perfection.
Theology
Aquinas’s God is not only the unmoved mover of the universe but also, according to Christianity, the creator of the world. Therefore, God, in thinking of Himself, knows all creation. For Aquinas, one of the fundamental tasks of reason is the demonstration of the existence of God. He argued that God’s existence must be demonstrated because, although it is self-evident (as the subject implies the predicate and is an analytic truth), it is not evident to us. Thus, Aquinas distinguished between two types of evidence:
- Propositions whose truth is self-evident to us: These are propositions whose truth is immediately grasped by human reason. All axioms are propositions of this kind.
- Propositions whose truth is self-evident but not to us: These are propositions that, while being self-evident in themselves, require demonstration for us to understand their truth. This is the case with the proposition “God exists.” It is self-evident in itself (a matter of faith) but not evident to human reason.
Therefore, the existence of God must be demonstrated. The appropriate theoretical procedure, according to Aquinas, is the demonstration a posteriori, which starts from the effect to demonstrate the cause. By considering the beings of the world as effects, we can argue for God as their cause. The a priori proof, which starts from the existence of the cause to demonstrate the effect, does not apply in this case because the existence of God (the cause) is what we are trying to prove.
Aquinas proposed five ways to prove the existence of God:
- From motion: Observing the movement in the world, we can infer the existence of an unmoved mover, which is God.
- From efficient causes: Recognizing the chain of efficient causes, we can conclude that there must be an uncaused cause, which is God.
- From contingency: The existence of contingent beings implies the existence of a necessary being, which is God.
- From degrees of perfection: The existence of degrees of perfection in beings suggests the existence of a most perfect being, which is God.
- From the order of the universe: The orderly and rational behavior of natural things points to the existence of an intelligent designer, which is God.
God is thus considered the unmoved mover of the universe (pure act), the uncaused cause (creator), the necessary being, the perfect being, and the intelligent designer of nature. God governs the universe through the eternal law, which regulates all beings in different ways: physical beings are governed by the laws of physics, while humans are governed by natural law (moral law), which respects their freedom.
Epistemology
Reason and Faith
Aquinas, like Aristotle, believed that human understanding is based on sensory experience. Therefore, the object of rational knowledge is sensible (material) reality. Consequently, our rational knowledge of God is imperfect and based on analogy (comparison). Aquinas argued that rational knowledge can be extended through faith (supernatural truth or revelation). He distinguished between two sources of knowledge: faith and reason, and saw no contradiction between them. The content of reason and faith can overlap; there are truths that can be reached both by reason and by faith. Thus, theology and philosophy are distinguished not primarily by their content but by their sources of knowledge. Both are autonomous and independent but cooperate with each other. Reason helps to build theology, and faith helps reason by providing extrinsic criteria and a negative test for rational knowledge (if philosophy leads to contradictions with revealed truth, there is an error in reasoning that should be reviewed).
Human Knowledge
Aquinas affirmed the need for axioms, first principles that govern all reality (these are numerous and are all derived from the principle of non-contradiction). Human understanding is linked to a material body equipped with organs of knowledge (the senses), as our object of study is material beings that we perceive. Universal knowledge of essences begins with sensory experience and cannot be achieved without it. The understanding performs abstraction, moving from the particular to the universal substance of each object. Aquinas distinguished two capacities of understanding: the active intellect, which abstracts representations from sensory data to form intelligible species (universal concepts) that express the essence of beings, and the passive intellect, which can then build upon these universal concepts.
Aquinas’s Anthropology, Ethics, and Social Theory
Anthropology
Man is a substantial union of body and soul. The rational soul is his essence and has several faculties: the vegetative faculty, which enables nutrition and development; the sensitive faculty, which enables sensation; and the rational faculty, which enables thought. For Aquinas, while the body decays and dies, the rational faculty of the soul is subsistent and incorruptible.
Ethics
Aquinas accepted the teleological conception of nature and the basic principles of Aristotelian ethics, stating that the ultimate end of man is happiness. This is achieved through the perfect development of our nature (our own good), and this development is driven by an inherent natural tendency. Perfect happiness is achieved through the contemplation (intellectual activity) of the transcendent supreme being (God), as this is the highest object of understanding (“the supreme good”). The basic and general moral laws that should guide human conduct are implicit in our soul (the essence or good) and constitute the natural law. This is how the eternal law, imposed by God on all beings in the universe, is manifested in man, respecting his freedom. By following natural law, man can come to know and unite with God, achieving, though not in this life, supreme and perfect happiness. The habit by which we tend to follow the precepts of natural law spontaneously is called synderesis.
The content of natural law is evident (knowable by any man), universal (applicable to all humans), and immutable (it does not change throughout history or across cultures) because it is based on human essence. For Aquinas, natural law, like the axioms of knowledge, has several precepts that are self-evident to us. Just as there is a basic axiom in theoretical demonstration (the principle of non-contradiction), there is a first rule or principle of practical reason (natural law) that is based on human essence (the good) and its development. The first precept, upon which all others are based, is “good is to be done and pursued, and evil is to be avoided.” From this first general precept, three primary precepts are derived, corresponding to each of the faculties of the soul:
- The duty to preserve life, which rationally develops the vegetative power and the natural tendency to survive.
- The duty to procreate and raise children, which rationally develops the sensitive faculties and the natural tendency towards sexual relations.
- The duty to seek the truth and to respect social justice, which develops reason and sociability, enabling us to attain knowledge, especially of God.
Natural law consists not only of these primary precepts but also includes secondary precepts, which are specific rules deduced from the primary precepts through rational reflection or conscience. These secondary precepts are generally common to all men, although there may be differences due to poor education, the dominance of desires over reason, or flaws in reasoning or essence. These precepts are also generally unchanging, although there may be exceptions when it is impossible to observe a particular precept for some reason.
Social Theory
The precepts of natural law are very general and must be concretized in society through social laws (positive laws). Living in society is inherent in human nature, and laws should be established to allow humans to comply with natural law. Positive laws are conventional and should be an extension of natural law, always respecting its content. For Aquinas, good governance is that which provides for the common good, with laws that respect and facilitate the realization of natural law, and with it, justice (the link between morality and law). Civil disobedience is lawful when the ruler’s intention is to pursue selfish ends (tyranny). The best forms of government, according to Aquinas, are Monarchy, Aristocracy, and Democracy.