Aquinas: Essence, Existence, and Demonstrations of God’s Existence
Thomist Theory of Ontological Distinction
In classical philosophy, a direct distinction between essence and existence was absent. Substance was defined by what things are. Existence, the fact that things are, wasn’t a primary problem for Greek philosophers, as they viewed reality as eternal. Their focus was explaining change within existing reality.
Christian philosophers, however, considered material reality non-eternal, necessitating explanation. All material is contingent, implying it could not have existed, thus distinguishing essence and existence. St. Thomas Aquinas believed essence isn’t merely shape but hylomorphism: the composition of matter and form. Existence is an attribute of reality independent of essence. For Aquinas, essence is a potential, a power, actualized by the act of being. The contingency of the world points to the necessity of God’s existence.
A Posteriori and A Priori Demonstrations
Aquinas believed natural reason could explain much, even truths of faith, most importantly, God’s existence. He criticized a priori demonstrations, reasoning from cause to effect, arguing we lack the knowledge to derive God’s existence from His definition.
Following Aristotle, Aquinas asserted human knowledge originates in sense, in sensible realities. Therefore, his proofs are a posteriori, arguments proceeding from effect to cause, from our world back to God. He established five starting points, five transcendentals of material beings, leading through a chain of causes and effects to the necessary existence of God as the first cause.
General Structure of Demonstrations of God’s Existence
Thomas sought to explain phenomena, from physical structures to metaphysical principles, even truths of faith, through natural reason. He criticized a priori demonstrations, arguing insufficient knowledge of God’s nature prevents deriving His existence from it.
Like Aristotle, Thomas defended a posteriori demonstrations, moving from effect to cause. These are based on natural phenomena, tracing back to God as the cause. He identified five starting points, natural phenomena of material beings, applying a metaphysical principle showing the need for an external cause, which itself requires a cause.
The chain of cause and effect cannot be infinite; without a first cause, the observed effect couldn’t exist. Aquinas concluded that this first cause is God.
The Way of Analogy and the Path of Negationis
Aquinas believed we can know something of the divine nature through analogy or eminence, a Neoplatonic principle of degrees of perfection. Beings are hierarchically ordered by their participation in the perfect. Yet, despite the analogy, a disproportion exists between creature and Creator, the finite and the infinite. Aquinas concluded we cannot know God’s essence from creatures.
According to Aquinas, reason reveals God’s existence, but not His essence. We know God better by what He is not than what He is. The five ways conclude with negation: a being without movement, contingencies, or cause—static, self-caused, necessary. However, we don’t fully grasp these transcendentals when attributed to God.
Our knowledge concerns the temporal and finite, while we affirm God as eternal and infinite. This indirect approach to God is called negative theology.