Thomas Aquinas and the Philosophy of Being: Why We Exist

Have you ever stopped to ask yourself, “Why do I exist?” or “What does it mean to be?” These are deep questions that can feel overwhelming, but they’re exactly the kind of questions Thomas Aquinas loved to explore. His philosophy of being, or "ontology," helps us understand the nature of existence and how everything points back to God. Let’s unpack his ideas in a way that’s easy to understand, with examples and analogies you can relate to.

What Does “Being” Mean?

In philosophy, “being” simply means something that exists. Aquinas said there are two key aspects to being:

1. Essence: What something is (its nature or identity).
   
• For example, a chair’s essence is being an object designed for sitting.
2. Existence: That something is (the fact that it actually exists).
   
• A chair you’re sitting on exists, but a chair you imagine in your mind doesn’t.

For Aquinas, only God’s essence and existence are the same. Everything else—like you, me, and the world around us—has an essence that depends on God for its existence.

An Analogy: The Lightbulb and Electricity

Imagine a lightbulb. The lightbulb’s essence is being an object that can give light. But for it to actually shine, it needs electricity. Without electricity, the lightbulb is just a bulb. Similarly, Aquinas taught that everything in the universe needs something to give it existence—and that ultimate source of existence is God.

Why Does This Matter?

Aquinas believed that understanding being helps us see God’s role as the foundation of all reality. The Catechism of the Catholic Church (CCC) echoes this idea:

“God is the fullness of Being and of every perfection, without origin and without end” (CCC 213).

This means that God isn’t just another thing in the universe—He’s the reason anything exists at all.

Contingent vs. Necessary Beings

Aquinas also made an important distinction between two types of beings:

1. Contingent Beings: Things that could either exist or not exist, like people, animals, and plants. We weren’t always here, and one day, we won’t be.
2. Necessary Being: Something that must exist and cannot not exist. For Aquinas, this is God.

Aquinas argued that if everything were contingent, there would have been a time when nothing existed. But since things do exist, there must be a Necessary Being that started it all—God.

An Everyday Example: A Stack of Books

Picture a stack of books on a table. Each book depends on the one below it to stay in place. But the stack can’t stand unless there’s a table holding everything up. In the same way, everything in the universe depends on God to exist. God is like the table—the ultimate foundation.

God as Pure Being

Aquinas taught that God is “Pure Being,” meaning He doesn’t just have existence—He is existence. Everything else borrows its existence from Him. The Catechism explains this beautifully:

“In God, essence and existence are one and the same” (CCC 212).

Why Is This Compatible with Science?

Some people think faith and science are at odds, but Aquinas’s philosophy shows they can work together. Science studies the “how” of the universe—how things work and change. Aquinas’s philosophy of being asks the “why”—why anything exists at all. Together, they give us a fuller picture of reality.

For example:

• Science might explain how gravity works, but Aquinas would ask, “Why is there gravity instead of nothingness?”
• Science can describe the Big Bang, but Aquinas would point to God as the reason for its existence.

Conclusion

Thomas Aquinas’s philosophy of being helps us understand the nature of existence and how everything depends on God. By reflecting on what it means to exist, we can see God as the ultimate source of all reality. For Catholics, this understanding deepens our faith and helps us grow closer to the Creator who gives us life.

The next time you wonder why anything exists, remember Aquinas’s insights: behind everything that is, there is a God who simply is.

References

• Aquinas, Thomas. Summa Theologica. Translated by Fathers of the English Dominican Province. Benziger Bros., 1947. Available online at: New Advent.
• Catechism of the Catholic Church. Online at Vatican.va.
• Feser, Edward. Scholastic Metaphysics: A Contemporary Introduction. Editiones Scholasticae, 2014.
• Kreeft, Peter. A Shorter Summa: The Essential Philosophical Passages of St. Thomas Aquinas’s Summa Theologica. Ignatius Press, 2001.