Ontology is the branch of philosophy that studies being.

Metaphysics asks:

What is reality like?

Ontology asks:

What exists in reality?

They overlap heavily, but they’re not identical.

The word “ontology” comes from the Greek “ontos” (being) and “logos” (study or discourse).

But to understand it properly, we have to unpack what philosophers actually mean by being, because it doesn’t mean “existing” in the casual sense people use in everyday speech.

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Ontology asks the deepest structural question philosophy can ask:

What is there?

And immediately after that:

What is the fundamental structure of what exists?

Not what we believe exists.

Not how we know things.

Not how things appear.

Ontology is concerned with what reality is made of at the most basic level.

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꩜ The Core Question

Ontology begins with a deceptively simple problem.

When you look at the world, you see:

• objects

• people

• events

• properties

• numbers

• ideas

• laws of nature

• space

• time

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The ontological question is:

Which of these actually exist, and in what way?

For example:

Does a chair exist?

Yes — but what exactly is a chair?

Is it:

• the atoms that compose it?

• the shape arranged by those atoms?

• the function of sitting?

• a concept in human minds?

Ontology studies what kind of thing a thing is.

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꩜ The Classic Ontological Categories

Most ontological systems converge on roughly five fundamental kinds of being. Different philosophers name them slightly differently, but the structure is remarkably stable.
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First: Substances

Substances are entities that exist in themselves rather than in something else. They are the basic “things” that can carry properties.

Examples:

• a tree

• a human being

• a mountain

• an electron

A substance can change color, shape, location, or temperature and still remain the same underlying thing. Aristotle treated substances as the primary units of reality—the core objects around which everything else hangs.

The key feature: a substance does not depend on another entity to exist as what it is.

A property needs something to belong to.

A relation needs things to relate.

A substance stands on its own.

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Second: Properties

Properties are features or attributes that things have.

Examples:

• redness

• mass

• temperature

• intelligence

• roughness

Properties cannot exist independently. “Redness” cannot float around the universe by itself; it always belongs to something red.

Philosophers divide properties into two major types.

Intrinsic properties belong to a thing by itself.

Example: the mass of a rock.

Extrinsic properties depend on relationships with other things.

Example: being taller than someone else.

Properties describe what something is like.

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Third: Relations

Relations describe how things are connected to each other.

Examples:

• larger than

• next to

• causes

• owns

• part of

Relations require multiple entities.

You cannot have “taller than” without two things being compared. You cannot have “causes” without at least two events.

Relations structure the network of reality. They are the glue that organizes substances and their properties into a coherent world.

Physics, interestingly, increasingly describes reality in relational terms—fields interacting, forces connecting objects, spacetime curvature linking mass and motion.

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Fourth: Events

Events are occurrences in time. They are things that happen.

Examples:

• a lightning strike

• a conversation

• a star exploding

• a thought forming in your mind

Events are processes unfolding through time.

Some philosophers think events are actually the most fundamental category of all. This view is called process ontology. Instead of objects being primary, the universe might fundamentally be made of ongoing processes.

A river is not a fixed object. It is flowing water.

A flame is not a thing. It is a continuous reaction.

In this view, reality is less like a pile of objects and more like a field of activity.

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Fifth: Abstract Objects

Abstract objects exist outside space and time.

Examples:

• numbers

• mathematical structures

• logical truths

• sets

• geometric forms

The number “2” is not located anywhere. You cannot bump into it, weigh it, or destroy it. Yet mathematics behaves as if these things are real.

This leads to one of the biggest ontological debates in philosophy.

Platonism says abstract objects truly exist in a timeless realm.

Nominalism says they are simply useful descriptions humans invented.

Mathematics working so well in physics is one of the reasons this debate refuses to die. Something strange is happening there.

So if we step back, the simplified ontology of reality looks like this:

Reality contains:

• Substances — things

• Properties — what things are like

• Relations — how things connect

• Events — what happens

• Abstract structures — patterns that describe everything

Almost any statement you can make about the universe falls somewhere inside that structure.

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“The apple is red.”

Apple → substance

Red → property

“The apple is on the table.”

Apple + table → substances

On → relation

“The apple fell.”

Falling → event

“2 + 2 = 4.”

Numbers → abstract objects

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꩜ The Central Ontological Debates

Ontology is where philosophy gets extremely deep very fast.

Some of the biggest debates include:

Materialism

Only physical matter exists.

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Dualism

Both physical and non-physical things exist (mind, soul, etc).

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Idealism

Reality is fundamentally mental.

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Platonism

Abstract objects like numbers exist independently of the physical world.

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Nominalism

Abstract objects do not exist — they are just names we give to patterns.

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Monism vs Pluralism

• Monism — reality is made of one fundamental substance

• Pluralism — reality contains multiple fundamental types

These debates are basically arguments over the basic ingredients of the universe.

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꩜ Ontology and Science

Interestingly, ontology overlaps heavily with physics.

Physics asks questions like:

• Are space and time fundamental?

• Are particles real or just excitations in fields?

• Is the universe made of information?

• Do multiple universes exist?

These are ontological questions, even when scientists are the ones asking them.

Physics produces models,

Then Ontology asks:

What do those models say actually exists?

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꩜ The Deepest Ontological Question

If you push ontology all the way down, you eventually hit the ultimate question:

Why is there something rather than nothing?

It’s the ultimate head scratcher.

First off, “nothing” is a slippery concept. What does it even mean? A total void, with no space, time, laws of physics, or even the potential for anything? If that’s the case, why would we expect nothing to be the default state? In my “view,” existence might be the baseline because nothingness is inherently unstable or impossible.
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Let’s Think about it: In quantum mechanics, particles pop in and out of existence in vacuums all the time—virtual particles borrowing energy from nowhere and vanishing again. Scale that up, and maybe the universe itself is a grand fluctuation. Nothingness isn’t empty; it’s possibility. So, “something” emerges because the alternative isn’t as neutral as it sounds.

If every conceivable state exists somewhere (in some branching reality or ensemble), then “nothing” is just one option among infinities, but we’re here observing “something” because only in a something-universe can observers exist to ask the question. That’s the anthropic principle in a nutshell: We couldn’t ponder nothingness if there were nothing.

My gut feeling? I think “something” wins because potential is baked into reality. Non-existence can’t enforce itself. There’s no mechanism to prevent being from bubbling up. If there were truly nothing, there’d be no rules saying it has to stay that way. It’s almost inevitable.

Even the idea of “nothing” presupposes some kind of structure—a total absence that we can conceive of. But conception itself is a form of existence. If nothingness were truly absolute, there’d be no properties, no laws, no “rules” to maintain it. Without any enforcement mechanism, what’s stopping a spark of potential from igniting? In my reasoning, potential isn’t an add-on; it’s primordial. It’s like the zero-point energy in physics—even in a vacuum, there’s fluctuation because emptiness isn’t inert; it’s teeming with latent possibility.

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꩜ Mereology (Parts and Wholes)

Mereology is the branch of ontology that studies how parts form wholes.

At first this sounds trivial, but it becomes strange very quickly.

Every object you encounter appears to be made of smaller parts.

let’s go back to the chair.

A chair contains:

• wood

• screws

• glue

• fibers

• atoms

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So philosophers ask:

When do parts actually become an object?

Because technically, the universe is just particles arranged in different ways.

So what makes a chair real instead of just a pile of atoms?

There are three major positions.

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Mereological Nihilism

Only the smallest fundamental particles truly exist.

Objects like chairs, cars, or mountains are just convenient descriptions we use for particle arrangements.

Under this view:

The chair does not really exist.

Only atoms exist.

This sounds extreme, but many analytic philosophers take it seriously.

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Universalism

Any collection of objects automatically forms a new object.

If you take:

• the Eiffel Tower

• your left shoe

• a cloud

Then together they form a real object.

Philosophers jokingly call this “the Eiffel-shoe-cloud object.”

Universalists accept that such bizarre objects exist because they think composition always occurs.

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Restricted Composition

Most philosophers settle here.

Parts form wholes only under certain conditions.

Examples:

• biological organisms

• functioning machines

• integrated systems

The challenge is defining the rule that determines when parts become a real object.

This is called the Special Composition Question.

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꩜ Objects vs Processes — Process Ontology

Most people assume the universe is made of things.

Tables, Planets, Animals, Atoms

This is called substance ontology.

Reality consists of objects that possess properties and undergo change.

This idea comes largely from Aristotle.

But another tradition argues something very different.

Reality might actually be made of processes, not things.

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Process Ontology

Under process ontology, objects are stable patterns inside ongoing activity.

Examples:

A river looks like a thing, but it is actually flowing water.

If the water stops moving, the river disappears.

A flame is not a static object.

It is a continuous chemical reaction.

Your body constantly replaces cells.

Metabolism is ongoing chemical activity.

You are not a fixed object — you are a process maintaining stability.

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So ontology asks:

Are objects fundamental, or are processes fundamental?