Substance, nature, and necessity › What substance means

Imagine receiving a message that sounds contemptuous. You begin composing a reply before asking whether you have understood it. Later, after learning what prompted the message, the same words seem different. Your reaction had causes, and the new understanding also becomes part of what determines your response. Does admitting those causes make the difference between an impulsive reply and a considered one disappear?

Baruch Spinoza's Ethics develops an account of freedom that depends on preserving that difference within a world governed by necessity. The message is a contemporary illustration, rather than an example from the book. Spinoza denies an absolute free will that stands outside causal determination. Yet he distinguishes being acted on through inadequate understanding from acting through adequate understanding. His ethical question is how a person can become more active in that sense.

The argument reaches that question through an account of reality as one infinite substance. Definitions and numbered proofs about God precede discussions of desire, emotional conflict, and human freedom. The connection is deliberate within the work: understanding ourselves requires understanding our place in nature. But neither its geometric form nor the ambition of its system makes its conclusions immune to criticism.

In Part I, definition III, Spinoza defines substance as what is in itself and conceived through itself. This concerns both existence and explanation. A substance does not depend on something else in the way that a state or modification depends on that of which it is a state. The definition is more demanding than the ordinary use of "substance" to mean material such as wood or water.

He distinguishes substance from an attribute and a mode. An attribute is what the intellect perceives as constituting the essence of substance. A mode is a modification that exists in, and is conceived through, something else. These definitions provide the vocabulary through which the later argument will distinguish God from finite things.

Consider the difference between explaining a particular wave and explaining the water of which it is a modification. This can illustrate dependence, but it cannot serve as a literal model of Spinoza's system. An ocean is a finite physical thing with surrounding conditions. Spinoza's substance is not a very large material object, and the attribute of thought cannot be explained away by extending the water analogy.

The distinction also prevents a common confusion about monism. Saying that only one substance exists does not mean that every finite thing is identical with every other finite thing. Spinoza can distinguish a particular body from another body while denying that either is a self-sufficient substance. Difference among modes and plurality of substances are different claims.