Spinoza’s Ontology

Modern philosopher Baruch Spinoza (1632 – 1677) was a rationalist philosopher in the modern tradition of Rene Descartes, Gottfried Leibniz, and Nicolas Malebranche. However, Spinoza was also famously a substance monist. And substance monism turns out to be a key to understanding Baruch Spinoza’s ontology.

A graphic of a human head in the cosmos looking at the sun
Image by Gerd Altmann from Pixabay.

Substance Monism

Substance monism is the theory that only one kind of substance exists. Philosophers contrast substance monism with substance dualism, which is the position that Descartes held. Substance dualism is the view that two distinct kinds of substances exist.

Spinoza calls this one substance both “God” and “nature”, both terms of which have important philosophical implications. By referring to the one substance as God, Spinoza seems to be taking a pantheist view. On the other hand, by referring to it as nature, he also seems to be advocating a naturalist position. 

Pantheism is the view that everything that exists is somehow identical with God or that the universe as a whole and everything in it is God. Naturalism is the view that only natural laws and forces exist or that everything that exists is natural in a scientific sense. So according to Spinoza, everything that exists is both God and nature.

Substance as Independence

Spinoza defines a substance as, “what is in itself and is conceived through itself, i.e., that whose concept does not require the concept of another thing, from which it must be formed.” Descartes defines substance similarly: an independent entity or an entity that does not need anything else in order to exist.

Whereas a characteristic, attribute, or property would require a substance or an entity to exist within, a substance itself does not. In addition to being infinite, substance in Spinoza is both self-caused and eternal. Philosopher often attribute these characteristics to God in traditional ontology. 

Attributes in Spinoza’s Ontology

According to Spinoza’s onology, the one substance that is God or nature has an infinite amount of attributes or characteristics. However, Spinoza believes that only two attributes are intelligible to the human mind: extension and thought.

In Descartes’s dualistic ontology, he characterizes the two different substances, body and mind, by extension and thought as well. But whereas in Descartes these two essential attributes belong to two distinct substances, for Spinoza there is only one substance.


Like Descartes, in Spinoza’s ontology substances also have modes. For Spinoza, modes are properties of a substance derived from and therefore ontologically dependent upon attributes. For Spinoza, ordinary objects like hammers, trees, camels, stones, and people are modes of substance. 

Spinoza argues that modes are causally linked and deterministic. However, there are two different causal systems for each of the two types of attributes. So, there is both a physical or material system of causation for extended modes and a system of mental causation for mind or mental modes.

The two deterministic causation systems run parallel to each other and do not causally interact with each other. Scholars and philosophers know this as Spinoza’s  ontological parallelism

Because modes are dependent upon substances for their existence, substances have a type of ontological priority or “higher status” than modes

Causal Determinism in Spinoza’s Ontology

For Spinoza, everything that occurs in a system is causally deterministic and strictly necessary. There are no contingent entities or events. This seems to leave little space for free will unless once supposes a kind of compatibilism between complete deterministic causality and freedom. 

However, Spinoza does leave some space for “freedom” despite what seems like a wholly deterministic and causally closed set of systems. For Spinoza, freedom is freedom of the mind or thought.And he characterizes this freedom “as blessedness.”

It is not entirely clear why one should equate freedom with blessedness. Or how one should interpret this as a form of freedom.

Realism and Idealism

Spinoza’s basic ontological definitions leave some ambiguity between a kind of realism and a kind of idealism. He seems to suggest that substance is both independent as what it is in itself (real) and as how we are able to conceive it (ideal). It is possible that for Spinoza, all objects (modes of substance) that humans encounter are both real in and of themselves but also ideal in that they are cognizable by us. 

According to Spinoza, everything that is extended is also fundamentally thought. This seems to imply that everything that exists has some sort of ideality attached to it. This could imply that everything that exists is in some way knowable by people, even if they are not completely knowable by people. Everything that is can give rise to an idea or thought.

The idea that entities for Spinoza have both a real and ideal component coheres with the way his one single substance gives rise to the two knowable attributes, extension and thought. Extension belongs to an object’s being physically extended in space. Entities have spatial dimensions like height, width, and depth. These are all characteristics of extension. 

God and Nature in Spinoza’s Ontology

One interesting implication of Spinoza’s ontology is that if everything is identical with God, and everything is fundamentally extended, then God is spatial. This contrasts with many philosophical and religious traditions. Such traditions do not conceive God as spatially located but rather He has no physical characteristics.

Like Gottfried Leibniz, Spinoza has a notion of the Principle of Sufficient Reason (PSR). For Spinoza, this manifests as the fact that all phenomena are explainable as a function of cause and effect.

If a given phenomenon manifests itself, to understand why this is so we simply need to look for its causes. This implies that everything that is in some way or really exists is scientifically understandable in terms of cause and effect. This is an expected consequence of Spinoza’s ontological naturalism or the view that the one existing substance is nature.

Philosophy of Mind and Mental Causation

Spinoza’s substance monism is an attempt to avoid the difficulties Descartes has with reconciling mind and matter and their causal interaction with each other.

Descartes conceived of mind and matter as two fundamentally different substances with completely different essences.

As a result, it was hard to see how Descartes’s matter could causally interact with a mind. And yet, it seems quite clear that our minds and our bodies interact with each other all the time.

Spinoza can seemingly avoid this Cartesian problem by positing that there is only one substance that is both mind AND matter. Therefore, it does not have to interact with some other substance completely different from itself causally.

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