6.1 Substance

The Concept of Substance in Metaphysics

Definition of substance in metaphysics

When philosophers talk about substance, they're asking one of the most basic questions possible: what is reality fundamentally made of? Substance refers to whatever exists independently and underlies everything else. It's not the color of a table or the shape of a rock; it's whatever that table or rock is at its core, independent of those surface-level properties.

This concept sits at the heart of metaphysics because it shapes how we answer bigger questions about existence, change, and identity. If you swap every plank on a ship one by one, is it still the same ship? (That's the famous Ship of Theseus problem.) Heraclitus raised a similar puzzle with his river: if the water is always flowing and changing, can you step into the "same" river twice? These puzzles only make sense once you start thinking about what substance is and how it relates to properties and change.

Different philosophers have proposed very different theories of substance, and those theories tend to fall into two broad camps: monism and pluralism.

Monism vs. pluralism in philosophy

Monism holds that there is only one fundamental substance or reality. Everything that exists is, at bottom, one thing.

• Parmenides argued that all of reality is a single, unchanging substance he called "Being." On his view, change and diversity are illusions.
• Spinoza (much later, in the 17th century) proposed that there is one substance he called "God" or "Nature," and everything in the universe is a mode or expression of that single substance.

Pluralism holds that reality is made up of multiple fundamental substances.

• Empedocles proposed four root elements: earth, air, fire, and water. Everything in the physical world results from the mixing and separating of these four.
• Leibniz argued for an infinite number of simple, indivisible substances called monads. Each monad is a self-contained unit of reality, and together they make up the universe.

Substance in Greek and Indian Philosophy

Form and substance: Aristotle vs. Plato

Plato and Aristotle are the two biggest names here, and they disagreed sharply.

Plato's Theory of Forms: The physical world around us is an imperfect reflection of eternal, unchanging Forms (or Ideas). The Forms are the true substances. A particular horse you see in a field is just an imperfect copy of the ideal Form of "Horseness." Physical objects come and go, but the Forms are permanent and perfect. So for Plato, the most real things aren't the objects you can touch; they're the abstract ideals those objects imitate.

Aristotle's Response: Aristotle thought Plato had it backwards. For Aristotle, individual objects (this horse, this table) are the primary substances. You can't point to "Horseness" walking around in a field. Aristotle kept the idea of form but built it into his account of physical objects:

1. Matter is the raw material or potential of a thing (the wood, the flesh).
2. Form is the structure or organizing principle that makes a thing what it is (what makes wood into a table, or flesh into a horse).

Aristotle also distinguished between primary substance (the individual thing, like Socrates) and secondary substance (the species or genus it belongs to, like "human" or "animal"). The individual always comes first in terms of what's most real.

Theories of substance across traditions

Greek philosophers weren't the only ones wrestling with substance. Indian philosophical traditions developed rich and independent theories.

• The Vaisheshika school proposed a pluralistic system with nine fundamental categories of substance: earth, water, fire, air, ether, time, space, soul, and mind. Each is a distinct type of reality, and physical objects are combinations of these basic substances.
• The Advaita Vedanta school took the opposite approach. This tradition is monistic: Brahman is the one ultimate substance, and the apparent diversity of the world is an illusion (called maya). Only Brahman truly exists.

Comparing these traditions with Greek philosophy reveals some interesting parallels. Both grapple with the monism vs. pluralism question, and both try to explain how substance relates to properties. A key difference is that Indian theories often carry a spiritual or religious dimension (Brahman in Advaita Vedanta is not just a metaphysical concept but a spiritual reality), while Greek theories tend to lean more on logic and observation.

No single theory has "won" this debate. Philosophers evaluate them by asking: Is the theory internally coherent? Does it explain our experience of the world? Does it account for both change and stability?

Ontological perspectives on substance

A few more terms round out the picture:

• Materialism holds that all substance is physical or material. There's nothing beyond matter and energy.
• Dualism holds that there are two fundamentally different kinds of substance, typically mind and matter. Descartes is the most famous dualist.
• Attributes are the essential qualities or characteristics that belong to a substance (for example, extension is an attribute of physical substance for Descartes).
• Persistence refers to how a substance maintains its identity over time even as its properties change. This connects back to puzzles like the Ship of Theseus: what makes something the same substance from one moment to the next?