One nature or many substances?

The reply you wish you had not sent

Imagine that a colleague calls Rafi’s work careless, and Rafi sends an angry reply before he has finished reading the criticism. “I chose to send it,” he says. But his sense of choosing tells him little about why this particular response felt irresistible.

For Baruch Spinoza, asking whether an action is free means asking how it arises, and that requires knowing what sort of being Rafi is. Descartes’s cogito established the thinker’s existence in the act of thinking, but it left further work to establish what that thinker is. Spinoza’s Ethics offers a striking answer: each of us exists as a particular expression of one substance. [1]

What exists through itself?

In ordinary speech, a substance might be flour or copper. Spinoza gives the term a stricter meaning: what exists in itself and can be understood through itself, so that explaining it does not depend on anything else.

An attribute expresses what substance essentially is. A mode is a particular modification of substance: it exists in something else and must be understood through it. Thought and extension, the nature of spatial reality, are attributes; particular thoughts and bodies are modes. Rafi, then, is not an independent substance that happens to interact with the rest of nature. His existence and activity depend on it. [1]

“In” does not mean being packed inside a very large container. The distinction concerns dependence: what can exist and be understood on its own, and what requires something else.

Why only one substance?

Spinoza arranges the Ethics like a work of geometry: definitions and starting principles, called axioms, followed by claims he sets out to prove. His conclusion is substance monism, the view that exactly one substance exists. The central steps run as follows.

First, in proposition 5, he argues that two substances cannot share an attribute. What could distinguish them? If their essential natures differ, their attributes differ. If only their modes differ, those dependent modifications cannot distinguish substances considered in themselves. [1]

Next, he defines God as absolutely infinite substance, possessing every attribute, and argues in proposition 11 that such a substance necessarily exists. His first proof relies on an earlier argument: substance cannot be produced by something else, so its existence must belong to its own nature.

Any second substance would therefore have an attribute that already belongs to God, which the first step rules out. Proposition 14 concludes that no other substance exists, and proposition 15 places everything else within that one substance, as its dependent modes.

The premises are demanding. A reader may challenge how Spinoza treats distinct substances, or ask whether existence really follows from the concept of substance. Setting out proofs in geometric form does not exempt their premises from examination.

God or Nature

Spinoza calls this reality “God or Nature.” God is the cause within which things exist, not a maker standing outside a separate creation. Nature here includes the reality expressed through thought as well as through extension, so the account does not reduce everything to ordinary material stuff. [1]

Nor does it erase differences. Rafi, his colleague and their messages remain distinct finite beings or events; being distinct simply does not make each an independently existing substance. Spinoza also treats a body and its idea as one thing expressed under different attributes, so thought and extension do not name two separate substances.

Necessity reaches our decisions

Spinoza denies that things could have arisen in any order other than the one that follows from God’s nature. Finite things, acts of will included, depend on other finite causes. Determinism means that events follow necessarily from their causes, and in Spinoza’s system that necessity extends to the whole order of nature. Our ignorance of causes does not open a gap in it. [1]

Rafi’s anger has causes, and so would a considered response: thinking the criticism through would itself belong to nature’s causal order. That does not make effort pointless, because an effect can depend on our effort as one of its causes.

How understanding can make us freer

Spinoza calls something free when it exists and acts from the necessity of its own nature, rather than being constrained by something external. Only God meets that definition without qualification. A human being remains vulnerable to forces beyond their power. [1]

Yet Spinoza also describes a free person as someone guided by reason. To explain how, he distinguishes acting from being passive. An adequate cause is one through which its effect can be fully understood. We act insofar as what happens can be understood through our own nature; we are passive insofar as we are only a partial cause of it. A passion is an emotion in which we are passive. The ethical task is to become more active through understanding, within the limits of being human.

Suppose Rafi comes to understand how fear of humiliation drives his urge to retaliate. He examines the criticism and answers what is true in it, instead of trying to hurt his colleague. What has changed is what explains his response: insofar as understanding now guides him, he is more active in Spinoza’s sense. Merely delaying the reply, or feeling certain he is right, would not show that change.

Spinoza argues that understanding our emotions and their necessity can lessen their hold on us. He does not promise that one insight will remove anger or make us invulnerable. It gives freedom a practical direction instead: becoming better able to act through understanding.

Leibniz: many centers of perception

Gottfried Wilhelm Leibniz’s Monadology starts instead from many simple substances, which he calls monads. Simple means without parts, so a monad is not a tiny spatial pellet. Each has perceptions, which need not be conscious, and an internal principle of change. Created monads depend on God while remaining distinct substances. [2]

Leibniz denies that one created monad changes the inner state of another. Their states agree through an order God has established, called pre-established harmony, so that each expresses the same universe from its own perspective.

This is substance pluralism: many substances, where Spinoza allows only one. Counting ordinary objects would not settle the disagreement, because it concerns what makes such objects possible. Nor does Leibniz’s plurality give us an automatic argument for uncaused choice; his full account of freedom lies beyond this contrast.

Try the reply again

Rafi says, “If my reply was necessary, understanding my anger cannot matter. And if Leibniz is right that there are many substances, I must be free to choose without causes.” Where does each conclusion outrun its support? This exercise is optional.

Read a possible response

Both conclusions outrun their support. Necessity does not make understanding causally idle: for Spinoza, understanding can help explain why someone responds through reason instead of being swept along by a passion. The two imagined replies differ in their causes; they are not two outcomes available with every condition held identical. A calmer reply alone would not prove that Rafi understands himself, but insofar as understanding guides him, he becomes more active while remaining part of nature. The second conclusion runs two questions together: how many substances exist, and whether choices have causes. Accepting many substances would still leave their activity and dependence to be explained, so plurality alone cannot establish uncaused choice.

Carry this forward

Ask two questions separately: what exists, and what makes an action ours? An answer to the first can reshape the second without settling it. Ideas, experience and a material world turns to experience and asks what our ideas allow us to know about a material world.

Sources and limits

[1] Baruch Spinoza, The Ethics, translated from the Latin by R. H. M. Elwes, Project Gutenberg eBook 3800, for the argument about substance, necessity and freedom. A locator such as IV.67 means Part IV, proposition 67. Read:

• Substance and necessity: Part I, definitions 1–8 and axioms 1–7; propositions 1–7, 11, 14–16, 18, 28–29 and 32–33, with their proofs, corollaries and notes; and proposition 17 with its proof and corollaries, but not its note.
• Thought and extension: II.1–2 and II.7, including their proofs and notes.
• Freedom: III, definitions 1–3; the complete Preface to Part IV; IV.4, IV.59 and IV.67; and V.3 and V.6, including their proofs, corollaries and notes.

The translation calls a scholium a “Note.” Its language is dated, and the web text contains apparent typographical errors. No comparison with the Latin or with a printed page was made, and the whole Ethics was not read.

[2] G. W. Leibniz, Monadology, Robert Latta translation revised by Donald Rutherford, 1997, for the contrast with Spinoza. Read §§1–17, 31–33, 47, 53–60 and 78–81, with the first editorial note; the contrast draws on §§1–17, 47, 56–57 and 78–81. The section numbers belong to the text itself; parenthetical references within it point to the Theodicy. No complete reading of the Monadology or the Theodicy, and no comparison with the French text, is claimed.

Sources accessed 18 September 2026. Rafi and the correspondence are original teaching material. Nothing in this selected comparison identifies Spinoza’s system with Vedānta or establishes historical influence. No independent scholarly review, learner testing or measured reading time is claimed.