Aquinas on Divine Simplicity and Pure Actuality

Hello! Welcome to our next lesson.

In our previous session, we established one of the cornerstones of Aquinas's metaphysics: the identification of God with ipsum esse subsistens (subsistent being itself). We saw how this conclusion, derived from the real distinction between essence and existence in creatures, provides the ultimate metaphysical foundation for Aristotle's concept of the First Mover as actus purus (pure actuality). A being whose very nature is the act of existing has no unactualized potential for being, and thus must be purely actual.

Today, we will explore a direct and powerful consequence of God's nature as pure actuality: the doctrine of divine simplicity. Our goal is to explain this doctrine and show its necessary connection to the concept of the mover being purely actual. In short, we will answer the question: why must a being with no potentiality also be a being with no parts?

1. What is Divine Simplicity?

In metaphysics, "simple" is the opposite of "composite." To say that God is simple is to say that God is not composed of parts of any kind. This is not to say God is "easy to understand"—quite the opposite. It means God is metaphysically non-composite and therefore radically different from everything in our experience, as all created things are composed of parts.

What kinds of parts or composition does this doctrine deny in God? Let's get an overview.

As the video explains, the doctrine of divine simplicity (DDS) asserts that God is not composed of:

• Physical parts (like a body).
• Metaphysical parts like form and matter.
• An essence and a separate act of existence.
• A substance and its accidental properties (like goodness or wisdom).

Now, let's build the core argument that connects this idea of non-composition directly to what we've already established about the First Mover.

2. The Argument: From Pure Actuality to Simplicity

The link between pure actuality (actus purus) and simplicity is direct and logically necessary. The central premise is this: any form of composition implies potentiality.

Here is the argument:

1. If a thing is composite, it is made of parts (let's call them A and B).
2. These parts, A and B, are distinct from the whole they compose (C). The parts are in potency to being unified into the whole.
3. For these parts to form a unified whole, their potential to be united must be actualized by some cause. This cause must be logically prior to the composite thing itself, as it is what brings the parts together to constitute the whole.
4. Therefore, any composite being is dependent on a prior actualizer for its unity and existence. It contains potentiality (the parts' capacity to be united) that has been actualized.
5. However, we have already established that the First Mover is actus purus—pure actuality, with no potentiality whatsoever.
6. Therefore, the First Mover cannot be composite. It must be absolutely simple.

This argument shows that simplicity isn't just an arbitrary attribute but a necessary feature of a being that is the ultimate source of all actuality. To be composed of parts is to be dependent and have unactualized potential, which contradicts the nature of a First Mover.

This next resource provides a concise, formal argument for this very point.

3. Deconstructing Composition: Why God has No Parts

Let's now apply this master argument to the specific types of composition we identified earlier. Each denial of composition in God is a direct application of the principle that God is actus purus and ipsum esse.

No Composition of Matter and Form

• Argument: Matter is, by definition, potency—the potential to receive a form. A being that is actus purus cannot have any potentiality. Therefore, God cannot be composed of matter. This also means God cannot be a physical body, since all bodies are material.

No Composition of Essence and Existence

• Argument: This follows directly from our last lesson. In any creature, the essence is in potency to the act of existing (esse). If God were composed of an essence that received existence, He would have potentiality and His existence would depend on an external cause. But as ipsum esse subsistens, God's essence is His existence. There is no distinction, and therefore no composition.

No Composition of Substance and Accidents

• Argument: This is one of the most profound consequences of DDS. In creatures, we distinguish between the substance (the thing itself) and its accidents (properties like being wise, strong, or good). These are potencies actualized in the substance. A person has the potential to become wise; wisdom is an accident they acquire.
• Since God is actus purus, He has no potentiality to gain or lose properties. Therefore, God cannot have attributes like goodness, wisdom, or power as distinct accidents. Instead, God is His goodness, is His wisdom, and is His power. In a simple being, the substance is identical to its attributes.

This next article elaborates on these points, walking through the logic from the conclusion of the Five Ways to the doctrine of simplicity.

4. An Apparent Contradiction: The Problem of Divine Attributes

This doctrine leads to a challenging conclusion: if God is simple, and God is His goodness and God is His power, then it seems to follow that God's goodness and God's power are identical to each other and to God Himself.

But this seems counter-intuitive. In our experience and language, "goodness" and "power" are clearly distinct concepts. How can they be one and the same in God? This is a classic objection to divine simplicity.

Aquinas's solution is to introduce a crucial distinction:

• Real Distinction: A distinction that exists in reality, within the thing itself. For example, the wheels and the engine of a car are really distinct parts.
• Logical Distinction (or Virtual Distinction): A distinction that exists only in the mind of the knower, not in the thing known.

Aquinas argues that the distinctions we make between divine attributes like goodness, power, and wisdom are logical, not real. Because our finite human intellects cannot grasp the single, infinitely perfect reality of God, we must use multiple, limited concepts derived from the perfections we see in creation. Each concept (goodness, power, wisdom) points to the one, simple divine reality from a different angle.

God's power is His goodness, which is His wisdom. They are one and the same in reality, but our minds conceive of them as distinct because we cannot comprehend their unified source.

For a more detailed textual treatment of this solution, section 5.1 of the paper "Divine Simplicity and Naming God" (resource LINK) is an excellent resource. It explains that "to say that God is omnipotent and omniscient is really to say that omnipotence and omniscience are identical in God," and the distinction exists only "in our minds, so as to make sense of our experience of them."

Conclusion

Today, we have seen how the doctrine of divine simplicity is not an optional add-on but a necessary deduction from God's nature as actus purus. By tracing the logic, we have arrived at a conception of the First Cause that is radically different from anything in the created order.

Here are the key takeaways from our lesson:

• Divine Simplicity is the doctrine that God is absolutely non-composite, lacking any physical or metaphysical parts.
• The connection to Pure Actuality is direct: any composition of parts implies potentiality (the potential of the parts to be unified) and requires a prior actualizer to unify them. A being of pure actuality, by definition, has no potentiality and requires no prior actualizer, and therefore must be simple.
• This simplicity means God is identical to his essence, his existence, and all of his attributes (perfections). God does not have goodness; God is Goodness.
• The apparent distinctions between attributes like power and wisdom are logical distinctions made by our finite minds, not real distinctions within God's simple nature.

By establishing God as ipsum esse subsistens and therefore simple and purely actual, Aquinas has built a robust metaphysical picture of the First Cause. In our next lesson, we will contrast how this Being acts as a cause with Aristotle's original, more limited conception. We will explore how Aquinas views God as both an efficient and final cause, whereas Aristotle saw his Unmoved Mover primarily as a final cause.