Thomas Aquinas: Faith, Reason, and the Existence of God

Posted on Nov 27, 2024 in Philosophy and ethics

The Harmony of Faith and Reason

Thomas Aquinas (TA) asserted that truth comes from God, thus precluding any true contradictions. While theological and philosophical truths occupy distinct realms, they cannot conflict. Any philosophical truth contradicting revealed truth indicates an error in the philosophical reasoning.

TA charted a middle course between the theory of double truth and the prevailing confusion. Like Augustine, he believed that faith and reason are separate but interconnected areas of knowledge.

According to TA, there are:

  • Natural truths accessible to reason alone, constituting its exclusive domain. Reason is self-sufficient in attaining these truths. Unlike Augustine, TA doesn’t posit that rational knowledge requires divine illumination.
  • Truths accessible only through faith, beyond the reach of human reason (e.g., the Trinity). These are articles of faith, the subject matter of sacred theology. This science, based on revelation and aided by reason, strives to make these truths understandable. This task, however, is entrusted to the Church, not to individual believers.
  • Truths discoverable by reason but also revealed (e.g., the existence of God). These truths, preambles of faith, are essential for salvation. Though reason can discover them, the process is complex, making them inaccessible to all. These truths are the subject of natural theology.

Thus, reason and faith collaborate within theology: philosophy clarifies revealed truth, while revelation expands philosophical knowledge. Any conclusions contradicting faith necessitate a review of the reasoning.

Philosophical Influences on Aquinas

Thomas Aquinas integrated Aristotelian principles with Platonic-Augustinian and Arab-Jewish thought to account for Christian doctrines not readily compatible with Aristotelianism.

From Aristotle, TA adopted:

  1. The theory of motion and the transition from potentiality to actuality.
  2. The hylomorphic theory of substance.
  3. The substance-accident distinction.
  4. The theory of four causes.
  5. The principle of analogy of being.

From the Platonic-Augustinian tradition, he incorporated:

  1. The theory of participation.
  2. The theory of emanation.
  3. The Neoplatonic theory of degrees of being.

From Arab and Jewish thought, he adopted the distinction between essence and existence.

Conception of God and the Five Ways

TA’s conception of God centers on creation: all existence results from divine creation. God, the uncreated being, is the ultimate cause of all beings. A radical difference separates God and humans: God exists necessarily and eternally, while created beings are contingent. In God, essence and existence are identical; in created beings, they differ, as their existence derives from God.

Regarding the demonstration of God’s existence, TA believed it demonstrable through reason, making it a matter of natural theology. He distinguished between two types of proofs:

  • A priori arguments (propter quid): demonstrating God’s existence from His essence, independent of experience (e.g., Anselm’s ontological argument).
  • A posteriori arguments (quia): starting from observed facts and tracing them back to their cause, identified as God.

TA criticized Anselm’s ontological argument, arguing that God’s essence is unknown, making it an unsuitable starting point.

TA favored a posteriori arguments, employing the following schema:

  1. Starting point: an observed fact.
  2. Application of the principle of causality at a metaphysical level.
  3. Rejection of infinite regress in the series of causes.
  4. Conclusion: identification of the first cause with God.

The Five Ways, following this inductive procedure, are:

  1. Motion: Observed motion implies a first unmoved mover, identified as God (inspired by Aristotle).
  2. Efficient Cause: The series of efficient causes cannot be infinite, requiring a first uncaused cause, identified as God (inspired by Aristotle and Avicenna).
  3. Contingency: Contingent beings imply a necessary being, the source of their existence, identified as God (inspired by Maimonides).
  4. Degrees of Perfection: The hierarchy of perfections implies a being of ultimate perfection, identified as God (inspired by Neoplatonism).
  5. Teleology: The order in nature, even in non-conscious beings, implies a directing intelligence, identified as God.