Spinoza, a prominent Rationalist, takes Descartes' definition of substance to its logical conclusion. While Descartes allowed for "created substances," Spinoza argues that if a substance is truly independent, there can only be one.
Spinoza identifies Substance with God and God with Nature. This is summarized in the phrase Deus Sive Natura (God or Nature).
"By substance, I understand that which is in itself and is conceived through itself." — Spinoza.
To explain how the one infinite substance relates to the diverse world we see, Spinoza introduces Attributes and Modes.
Attributes are what the intellect perceives as constituting the essence of substance. While God has infinite attributes, the human mind can only perceive two:
Crucially, these are not two different things, but two ways of looking at the same substance (Parallelism).
Modes are the modifications or "affections" of substance. They are the individual, finite things we encounter in the world—like a specific chair, a specific thought, or a specific person.
| Concept | Definition | Analogy (Ocean) |
|---|---|---|
| Substance | The ultimate, infinite reality. | The Ocean itself. |
| Attribute | Essential properties of the ocean. | The wetness or the saltiness. |
| Mode | Finite expressions/shapes. | The individual waves or ripples. |
Gottfried Wilhelm Leibniz rejected Spinoza's single substance and Descartes' dualism. Instead, he proposed Pluralism: the universe is made of an infinite number of simple, spiritual substances called Monads.
"The Monad... is nothing but a simple substance, which enters into compounds; simple, that is to say, without parts." — Leibniz.
If monads are "windowless" and cannot influence each other, how does the world seem so coordinated? Leibniz explains this through Pre-established Harmony. God, as the supreme monad, created all monads such that their internal changes perfectly correspond to one another, like two clocks set to the exact same time.
Common Pitfall: Students often confuse Spinoza’s "Attributes" with his "Modes." Remember: Attributes are essential and infinite, while Modes are accidental and finite.
Key Comparison: In a "Compare and Contrast" question:
Frequently Asked Question: "Why are Monads windowless?"
Answer: Because they are simple spiritual units. Physical interaction requires parts that can be moved or changed from the outside. Since monads are simple, all their changes must come from an internal principle.
Mnemonic for Spinoza: S.A.M. (Substance, Attribute, Mode).