What Is a Thing, and What Is It for That Thing to Exist?
Imagine you are thinking about a horse. You can picture it clearly: four legs, a mane, the way it moves. You know what a horse is. Now imagine you are wondering whether horses actually exist. Maybe you’re not sure—maybe someone told you horses are just a legend, like unicorns. You can still think about what a horse is without knowing whether any real horse has ever existed.
That gap—between what something is and whether it exists—is one of the most puzzling things philosophers have ever noticed. And for centuries, thinkers in the Islamic world argued fiercely about it.
Here’s a strange thing philosophers noticed: When you say “horses exist,” you seem to be saying two things at once. You’re saying what horses are (four-legged animals with manes) and you’re also saying that there are such things in the world. But are those two things separate? Or is saying “horses exist” just a fancy way of saying “horses are horses”?
The First Big Question: Are Essence and Existence the Same Thing?
Before we go further, we need some words to work with. Philosophers call the “what-it-is” of something its essence. The “that-it-is” is its existence. The question is: are these two the same thing, or are they different?
You might think this sounds like a weird game with words. But it matters a lot. If essence and existence are the same, then to exist just means to be something. A horse exists because it is a horse. A cup exists because it is a cup. If they are different, then there’s something extra—some mysterious “existence” that gets added to things.
The earliest Islamic philosophers mostly thought essence and existence were the same. Al-Kindī, a philosopher in the 9th century, said that “to be” just means “to be something.” When you say a cup is, you’re just saying it’s a cup. Nothing more.
But then came a philosopher named Avicenna (Ibn Sīnā, who lived around 1000 CE), and he disagreed. He changed everything.
Avicenna’s Big Move
Avicenna noticed something simple but powerful. You can think about the essence of something without knowing whether it exists. You can think about a triangle—what it means to be a triangle—without knowing if any triangle has ever existed. That means your idea of “triangle” and your idea of “exists” are different ideas. They can’t be the same thing.
This seems obvious, but it had huge consequences. If essence and existence are different concepts, then maybe they are also different in reality. Maybe when a horse comes into the world, two separate things happen: the horse’s essence gets joined with existence, like two Lego bricks clicking together.
Avicenna thought this was true for almost everything. The only exception was God. For God, Avicenna said, essence and existence are the same. God doesn’t have an essence that then receives existence. God just is existence. That’s what makes God special: God exists by His own nature, not because something else gave Him existence.
For everything else—horses, cups, humans, trees—existence is something added. And since existence comes from outside, everything except God needs a cause. This led Avicenna to a famous argument: if you trace the chain of causes backward, you eventually get to something that doesn’t need a cause—God, the one thing whose essence is existence.
But Wait: Does Existence Actually Exist?
Avicenna’s theory sounds neat, but other philosophers noticed a problem. If existence is something separate from essence, then existence must be something. It must exist itself. But if existence exists, then it needs its own existence. And that existence needs its own existence. You get an infinite staircase of existences, each one requiring another. That’s nonsense.
A philosopher named al-Suhrawardī (who lived around 1190) pushed this objection hard. He said: think about it. When you say “Socrates exists,” you’re not pointing at some extra thing called “existence” that floats around Socrates. You’re just saying that Socrates himself is real. There’s no separate “existence” stuff.
Al-Suhrawardī argued that “existence” is just a concept we use to talk about things. It’s like the word “individuality.” When you say “Socrates is an individual,” you’re saying something true, but there’s no extra “individuality” thing floating around Socrates. Same with existence. It’s a useful idea, but it doesn’t name anything real outside our minds.
This position is called conceptualism: existence is just a concept, not a real thing added to essences.
The Opposite Move: Maybe Essences Don’t Exist Either
If you’re keeping track, we now have two camps. Avicenna said essence and existence are both real but different. Al-Suhrawardī said only essences are real; existence is just a concept.
But then came Mullā Ṣadrā, a philosopher from the 1600s who flipped everything upside down. He said: maybe it’s the essences that aren’t real. Maybe what really exists is just existence itself.
Think about it this way. You look at the world and see horses, cups, humans. But what if those categories—“horse,” “cup,” “human”—are just how your mind slices up a single, flowing reality? What if there’s only one thing: existence, with different intensities? A horse is not a separate kind of thing from a human. A horse and a human are just different degrees of the same underlying reality, like different shades of blue.
This is called primacy of existence: what’s really real is existence itself. The essences we talk about are just mental shortcuts.
Mullā Ṣadrā didn’t just make this up. He was influenced by Sufi mystics who said that God’s existence is the only true existence, and everything else is just a reflection or manifestation of that one reality. For Ṣadrā, God doesn’t create essences and then give them existence. God creates existence, full stop. The essences—what we call “horses” and “humans”—are just the way that existence looks to us.
So Who Is Right?
Nobody really knows. Philosophers still argue about this today.
The whole debate moves in a circle. You start by thinking essence and existence are the same. Then you notice they seem different. Then you try to separate them and run into problems. Then you say existence isn’t real at all. Then you say essences aren’t real either. And then you wonder if you’ve just been playing word games the whole time.
But here’s why this matters: the answer changes how you understand everything.
If essence and existence are the same, then to exist just means to be something definite. The world is a collection of distinct kinds of things, and each thing just is what it is.
If essence and existence are different, then existence is something mysterious that gets poured into things. The world is less solid—things are not just themselves, they also have this strange “is-ness” added to them.
If only essences are real and existence is just a concept, then the world is a collection of definite things, and “existence” is just a label we put on them.
If only existence is real and essences are just concepts, then the world is a flowing, unified reality, and our categories are just useful fictions.
Think about your own life. Are you a definite kind of thing (a human, a student, a friend) who happens to exist? Or are you a bit of existence that happens to look like a human, a student, a friend? Does it feel different to say “I am” compared to “I am a human”?
These aren’t just weird questions for philosophers. They touch on what it means to be anything at all—including you.
Appendix
Key Terms
| Term | What It Does in This Debate |
|---|---|
| Essence | The “what-it-is” of something—what makes a horse a horse |
| Existence | The “that-it-is” of something—the fact that something is real |
| Conceptualism | The view that existence is just a concept in our minds, not a real thing |
| Primacy of existence | The view that existence is what’s really real; essences are just mental labels |
| Secondary intelligible | A concept that applies only to other concepts in our minds, not directly to real things |
Key People
- Avicenna (Ibn Sīnā) – A famous philosopher and doctor from around 1000 CE who argued that essence and existence are really different for everything except God.
- Al-Suhrawardī – A philosopher from around 1190 who argued that existence is just a concept, not something real outside the mind.
- Mullā Ṣadrā – A philosopher from the 1600s who argued the opposite: only existence is real, and essences are just how our minds slice up reality.
Things to Think About
- If existence isn’t a real thing added to essences, then what does it mean for something to come into existence? What changes when a baby is born or a tree grows?
- Avicenna said we can think of a triangle’s essence without knowing if triangles exist. But what if we can’t really think of an essence without some form of existence? Try it—can you really think of “horseness” without picturing a horse somehow?
- If only existence is real (like Mullā Ṣadrā says), then what makes one thing different from another? Are horses and humans really the same thing at different intensities? How would that work?
- Could the whole debate be a mistake? Maybe “essence” and “existence” are just two ways of talking about the same thing, and the confusion comes from thinking words must match separate pieces of reality.
Where This Shows Up
- Science fiction and fantasy – Stories about alternate universes, mirror dimensions, or virtual realities often play with the idea that “existence” is not simple. What does it mean to say something “exists” in a computer game?
- Biology – When scientists classify living things, they group them by essences (mammals, birds, reptiles). But those categories are human inventions that nature doesn’t perfectly obey.
- Everyday arguments – People argue about whether abstract things like numbers, justice, or love “really exist.” These are the same questions as the essence-existence debate, just with different examples.
- Religion – Many traditions ask whether God creates the essences of things or just their existence. That’s exactly the question these philosophers were debating.