What is God? God and Being

We’ve seen that God exists, not just as a conclusion of faith, but as the necessary foundation for all being. But this raises a deeper question: what does it mean to exist? And more specifically: what kind of existence does God have?

Aquinas offers a powerful and surprising answer: God is not just a being among other beings. He is Being Itself.

This idea is at the heart of Aquinas’s theology and metaphysics. It changes how we understand God and how we understand everything else.

Created Things: Act and Potency

Everything in our experience is a combination of act and potency. That is, things are actually some way now, but they could potentially be otherwise.

• A cold cup of tea is actually cold, but potentially hot.

• A student is actually learning, but potentially wise.

• A block of marble is potentially a statue.

Change, as Aquinas says, is the movement from potentiality to actuality. Everything in creation is constantly changing, constantly receiving, and constantly depending on something else.

We touched on this in the argument from motion: nothing moves (or changes) from potential to actual unless something already in act causes it to do so.

God Has No Potential; He Is Pure Act

But God is different.

God has no potency. He is not waiting to become anything. He does not depend on anything. There is no unrealized possibility in Him.

God is what Aquinas calls Pure Act (actus purus). He is the fullness of being, already and always complete. There is nothing missing, and nothing waiting to unfold.

This is why God is unchangeable. Change implies movement from less to more, from incomplete to complete. But God lacks nothing. He is fullness itself.

No Parts, No Limits, No Composition

Everything in creation is made of parts—matter and form, body and soul, essence and existence.

But whatever is made of parts must be put together by something else. It depends on something deeper than itself.

If God had parts, He would depend on those parts. He would not be self-sufficient. That is why Aquinas teaches that God is simple. Not because He lacks depth, but because He is not composed.

God’s essence is His existence. What He is and that He is are not separate. He doesn’t have being. He is being.

Ipsum Esse Subsistens: Being Itself

This is the boldest claim Aquinas makes: God is not a being, but Being Itself (ipsum esse subsistens).

Everything else “has” existence. Everything else receives being.

But God is existence. He does not exist in something. He is not contained by being. He is the very act of to be.

That means God is not one item among others in the universe. He is not a super-being. He is the very foundation of all existence—the One in whom all things live and move and have their being.

Why This Changes Everything

If God is Being Itself, then everything that exists is a gift. Nothing explains itself. Everything depends on something deeper. And at the bottom of it all is not chaos or randomness, but pure actuality, perfect fullness, and eternal love.

This also explains why God cannot be disproved by science. God is not part of the created order. He is not a thing in the universe to be found, measured, or examined. He is the reason there is anything to examine at all.

When Aquinas says “God is,” he is not stating a fact about the world. He is revealing the ground of all facts—the One who makes all “is-ness” possible.

Looking Ahead: The Trinity and the One Divine Nature

This understanding of God as Being Itself, indivisible and fully actual, lays the groundwork for approaching the mystery of the Trinity. If God were composed of parts, or merely one being among others, the doctrine of three Persons in one God would be impossible. But precisely because God is one, simple, and subsistent Being, it is possible for three distinct relations of origin to share that one divine nature without division or contradiction.

We explore this more deeply in a companion essay devoted to the Trinity:

👉 Deeper Dive into the Trinity

Coming Next: Can Science Point to God?

We’ve come a long way, following Aquinas step by step. But now we turn to a different kind of question. Can modern science, which studies the natural world, offer support for the existence of a Creator? Can what we know through physics, cosmology, and biology point us toward the One Aquinas called ipsum esse subsistens?

In the next post, we’ll explore that idea and see how faith and reason continue to walk together—even in the age of the atom and the telescope.