Faith & Science Icon Faith & Science

Essence and Existence: The Cornerstone of Thomistic Metaphysics

Michael Egnor

Metaphysics

Metaphysics is the study of the basic structure of reality. It is, in Aristotle’s words, the study of being as being, rather than the study of any particular being per se. Metaphysics is the framework by which we understand reality. We can’t avoid metaphysics — every act of understanding entails a metaphysical framework, a perspective. One might say that our metaphysical perspective is that by which we understand, contrasted to nature itself, which is that which we understand. 

Our own metaphysical framework is often opaque to us. We use it, like we might use an intuitive political bias, without really examining the framework we are using. We each have a metaphysical bias — it’s unavoidable, and the important question is: does our bias lead us toward or away from the truth? Gaining metaphysical insight is not easy, but it pays big dividends. It helps us to know the truth — indeed, it is that by which we know the truth.

A Rigorous and Consistent System

St. Thomas Aquinas developed a rigorous and consistent system of metaphysics. He was the first Christian philosopher to insist that faith and reason, properly understood, are never in conflict. Belief in God is not contrary to knowledge of the natural world. St. Thomas’ doctrine was controversial in his day, but it was accepted by the Church in the centuries after his death, and it became the intellectual foundation of the modern world, including the cornerstone of modern science. 

Ironically, the correspondence of faith and reason is controversial today, especially in the atheist community. The denial of the compatibility between faith and reason is a lynchpin of atheist arguments for naturalism: atheists insist that science tells us the real truth about the world, and faith in God is superstition. The Thomistic reply is that genuine faith and reason both point to the same truth. The Thomistic understanding of reason and its correspondence with faith offer a powerful reply to atheistic naturalism. For readers who are interested in metaphysics and in these modernist controversies (which readers of Evolution News are likely to be), it’s worthwhile taking a closer look at the principle that is the cornerstone of Thomistic metaphysics. 

Essence and Existence

The cornerstone of Thomistic metaphysics is the doctrine of essence and existence. It is this: essence is absolutely distinct from existence. This doctrine, which St. Thomas was the first philosopher to assert unequivocally and demonstrate with rigor, has profound implications for our understanding of reality, of nature, of science and of God. What does St. Thomas mean in saying “essence is absolutely distinct from existence”?

First, definitions. Essence is that which makes something the sort of thing it is. It is, succinctly, all the characteristics that are knowable about something. The essence of a cat is everything about the cat that makes it a cat. Its cat-shape, it’s furriness, its meow, its animality, etc. Some things about the cat — the fact, for instance, that at (unfortunate) times it can be a projectile launcher or a meal — are not parts of the essence of a cat. They are extraneous to it, although in rare circumstances, they may be true of it. You can see here where that modern notion of “essence” comes from. Essence is what’s important about something, what tells us what something really is. 

And Now for Existence

Existence is that a thing is, rather than what a thing is. The existence of a thing is different from the essence of a thing. I can know the essence of a rock, but it is the rock’s existence by which I stub my toe. I can’t stub my toe on essence, no matter how hard it is. 

Prior to St. Thomas, many philosophers considered existence to be a property of something, part of its essence. We might say that my cat Fluffy’s essence is that she is shaped like a cat, purrs and meows, likes to play with yarn, and exists. 

An Utter Metaphysical Distinction

St. Thomas emphatically pointed out that existence is not, and cannot be, any part of essence. Existence and essence are metaphysically utterly distinct — existence is not a genus, in scholastic terms, but is above every genus. Existence is not a characteristic or property of a thing. It is something much more fundamental. 

To understand what Aquinas is getting at, consider again my cat Fluffy. I will describe her to you: she is calico, weighs nine pounds, hates baths, purrs, says “meow” several times a day, is three years old, and is expecting kittens. If you want to know more about her, just ask. I can describe her in any degree of detail you would like. 

Now tell me this: does she exist? I have given you her essence, to any level of detail you want, but the fact or fallacy of her existence is not knowable from knowing her essence. In fact, I don’t have a cat. I have a dog. But I can describe my cat completely, and you still can’t know if she really exists. 

In Love with Unicorns

I can describe anything you like in whatever detail you like, but you can’t know whether it exists or not merely by its description. You can’t know existence merely by knowing essence. My daughters, when they were little, were obsessed with unicorns. They loved them, studied them, thought and talked about them all the time. They lived their silky mane, big bright eyes, pink or blue coat, shining horn, adorable tail, etc. Despite a passionate “science” of unicorn-ology — a mainstay of girlhood — no unicorn actually exists. Essence is not existence. In modern terms, the Venn diagram of existence has no overlap with the Venn diagram of essence. 

In Thomistic terms, in order for something in nature to exist, its existence must be joined to its essence. In fact, that is what nature is: distinct essences joined to existence. Things that exist are composites of existence and essence, and existence and essence are really distinct things. 

So what does this matter? It seems too esoteric to have any relevance to anyone not in a cloister. But it’s relevance is profound and extends to many aspects of theology and science. For the next post. 

Image: A captive unicorn, representing essence but not existence, from a tapestry in The Cloisters, New York City, via Wikimedia Commons.