Plato and St. Thomas Aquinas: Philosophy Compared
Plato’s Key Philosophical Concepts
Politics is a cornerstone in Plato’s philosophy. His primary objective is to define the virtues. Socrates argues that we must have something common to all possible conceptions of justice and courage. This common element, which he calls an “Idea,” would be seen as eternal and objective, not relative, as the Sophists claimed.
At this stage, Plato develops his theory of the duplication of the world, expressed in the Myth of the Cave:
- The sensible or material world is the most immediate reality to us, which we know through the senses.
- The intelligible world of Ideas is the real world, where Ideas are unique, eternal, and intangible. It is accessed through intelligence and represents true reality.
The soul is the bridge between both worlds. Plato affirms the existence of a world order in the Ideas: materials, mathematics, virtues, and property.
Plato’s Theory of Knowledge
In his dialogues, Plato develops three other ideas of human knowledge:
- Reminiscence: The soul, before incarnating with the body, already knew all Ideas.
- Dialectic as a mode of knowledge: Plato uses this term in two ways:
- As a dialogue (a question-and-answer game).
- As a science (contemplation of Ideas).
Plato distinguishes two kinds of knowledge:
- Opinion: This pertains to the sensible, material world and is subdivided into imagination and belief. This is the world of opinion found in the Sophists.
- Science: This pertains to the intelligible world; the goal is Ideas. It is divided into discourse intelligence (mathematics) and thinking (contemplation of an Idea).
Plato’s Anthropology
Plato’s anthropology is dualistic. He divides the soul into three parts:
- Rational (Rulers/Prudence)
- Irascible (Guardians/Fortitude)
- Concupiscible (Producers/Temperance)
St. Thomas Aquinas’s Philosophy
St. Thomas Aquinas holds that truth is unique and can be found through reason and faith. Reason knows from the data of the senses, and faith is based on divine revelation. The truths of faith cannot be proven rationally and must be accepted without discussion because they emanate from God. Truths of reason can be understood by human understanding and are rationally demonstrable.
Five Ways to Demonstrate God’s Existence
St. Thomas offers five ways to demonstrate the existence of God, sharing the same structure:
- It starts from an observation from experience.
- It applies the principle of causality.
- It concludes with the existence of God.
The five ways are:
- Movement: From the movement of the world to the First Unmoved Mover.
- Efficient Causality
- Contingency: From contingent beings to a Necessary Being.
- Degrees of Perfection: From degrees of perfection to a Supremely Perfect Being.
- Purpose and Cosmic Order
In God, essence and existence are mutually implicated because His nature is to exist and implies perfection.
Aquinas’s Anthropology
Man is conceived as a unique substance composed of matter (body) and form (rational soul). The human soul is immortal.
Thomistic Theory of Knowledge
Knowledge is understood as a process of abstraction. The soul dematerializes forms in the field, entering the final stage where it receives, through patient understanding, intelligible species and knows the overall concept.
Aquinas’s Ethics
Theological understanding is acquired through knowledge and virtue. God governs by the eternal law and involves creatures through natural law. Human acts correctly when following natural law. Practical reason, which is invariable, universal, and indelible, guides reason to do good and avoid evil. St. Thomas establishes a parallel between theoretical and practical reasons using principles of logic. Positive law must derive from natural law and seek the common good. Laws are legitimate if they respect natural law; otherwise, they are unjust.