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Spinoza's Concept of 'Substance'

In this essay we explore the concept of substance given by Spinoza in response to the earlier ideas of Rene Descartes. We examine how Spinoza’s concept deals with the inherent problems of Descartes’ dualism and how it attempts to dissolve the mind-body problem. Spinoza’s recourse to a single essential substance leads logically to a universal determinism and the denial of human freedom. We examine how Spinoza’s account of the emotions provides a concept of free will compatible to a degree with determinism. Finally, we relate Spinoza’s conception of reality with current ideas in modern physics that share a similar view of the unity of space, time, matter and energy.

Baruch Spinoza sought a theory of knowledge based upon certainty and the elimination of doubt. Unlike Descartes, Spinoza sought to establish grounds for certainty not through the first person perspective the cogito but by describing an impartial viewpoint on the world based upon a new concept of substance. To Spinoza, the cogito is an insufficient basis for certainty because it is based only upon a contingent truth (“I am thinking…”) and not upon a necessary truth. Influenced by the elegance, rigor and clarity of Euclid’s geometrical proofs, Spinoza sought an axiomatic method for deriving true knowledge (theorems) through the application of logic and inference rules upon a number of starting axioms - these being self-evident and true by necessity. The result of this geometrical method was the “Ethics” – an axiomatic exposition of metaphysics which gives a radical account of substance and then proceeds to develop a system of ethical behaviour compatible with the determinism that this entails.

Descartes’ account of substance has a number of inherent difficulties. Firstly, what the relationship between substance as essence, matter or ‘stuff’ and substance as an individual object? How many substances are there and how does a substance come into existence and sustain itself? For that matter, why do we need an account of the origin of substance in the first place? Spinoza saw that a new concept of substance was required to provide convincing answers to these questions and hence to underpin metaphysics, epistemology and science.

Spinoza sought to redefine Descartes notions of the principal and secondary qualities (attributes) of a substance and the modes (modifications) through which the essence of a substance is expressed or perceived. To Descartes, the principal attributes of a substance remain constant since they are the essence of the substance. Hence Descartes identified thought and extension as the principal attributes of the substances mind and matter respectively. The ‘modes’ or secondary qualities of a substance may change freely without the substance ceasing to be what it is. (For example, the colour, temperature or hardness of Descartes’ piece of wax.) Using Descartes’ ideas as a basis, Spinoza seeks to be more precise in the use of the terms ‘substance’ ,‘attribute’ and ‘mode’.

Descartes was inconsistent in using ‘substance’ to denote both individual objects and a generalised idea meaning “that which depends on nothing outside itself.” Spinoza’s definition is more distinct: “a substance does not depend upon the conception of another thing from which it might be formed” and “a substance is conceived in itself and conceived through itself.” In other words, a substance stands alone, is entirely self sufficient, internally consistent and fully intelligible apart from all other things. Thus substances cannot enter into relationships with each other and, in particular, a substance is not caused by and is not the cause of any other substance. A substance then must include within its essence its own cause – it must exist necessarily (causa sui).

In Spinoza’s terms, the attributes of a substance are those properties by which the intellect perceives its essence. Spinoza re-defines ‘modes’ as those properties of a substance which are not directly understood in themselves but must be understood through relation to another substance. The language here can be difficult to understand. Mode x is ‘in’ y if x can only be understood through an understanding of y. In other words, y is prior to x and is thus understood to be more fundamental or more real than x. For example, the modes of ‘the human body’ can only be understood through an understanding of the cells which constitute the body. Modes then are emergent properties of some more fundamental reality which can be arrived at through a recursive decomposition which terminates with the essential substance itself.

Since a substance cannot be further decomposed into anything on which it depends, all substances must be distinct and unique. Hence substances do not share attributes and do not enter into relations with each other. Here Spinoza makes his key move using his notion of substance and attribute to refine the ontological proof of God. To Spinoza, God must be a substance which has an infinity of attributes. This must be true by definition since God represents ultimate perfection and any substance with more attributes would necessarily be closer to perfection. If God has an infinity of attributes and no substances share attributes then there can only be one substance – namely God Himself.

If God has an infinite variety of attributes, then what are those attributes through which the intellect grasps the essence of God? To Descartes, extension and thought were attributes of two distinct and disjoint substances: mind and matter. Spinoza’s grand conception was to propose a unified model of reality – therefore dissolving a number of philosophical problems. While possessed of infinite attributes, claimed Spinoza, the divine substance is known to the human intellect only through the attributes of thought and extension. So far as the world is knowable, it consists of a single substance seen under two aspects: the aspect of thought being the essence of God and the aspect of extension being the aspect of Nature: Deus sive Natura – God or Nature.

Spinoza’s exact meaning here can be difficult to grasp since he does not say that thought and extension are separate attributes of God – they are actually separate essences of God. If they were merely attributes then the modes of one could be explained in terms of the modes of the other. The mind and ideas then are but finite modes of the aspect of thought; the body a finite mode of the aspect of extension. This is clearly a form of panpsychism since for every mode of extension there must be a corresponding mode of thought. Hence all objects are to some degree possessed of mentality. Replacing the dualism of Descartes we have a theory of dual aspects:

Mind and body are one and the same thing conceived now under the aspect of thought and now under the aspect of extension.”

To Spinoza it is meaningless to ask how the mind and the body can interact or how the creator gave rise to creation - these philosophical problems are merely illusions caused by the separateness of the aspects by which the underlying substance can be known. Physical processes then cannot be explained in terms of a mental process, just as an idea or logical progression of ideas cannot be explained in terms of a physical process. To Spinoza, they are in fact one and the same but conceptualised under different frames of reference that can never comprehend each other. This view can be likened to the comprehension of a painting under different aspects. One can understand the essence of the painting in terms of the arrangement of paint particles upon a two dimensional surface. At the same time the painting can be understood as a representation of the Madonna and Child. Any analysis couched purely in terms of paint particles wholly misses the other essence of the underlying object ( the ‘substance’). Similarly an account which talks solely about the relationship of the characters and their emotions tells us nothing about the chemistry of the lead oxides used in the paint.

Spinoza is surely treading a very fine line here in that he appears to embrace the dualist position (that mind stuff and body stuff are distinct, separate and different in essence) while affirming that they are aspects of a single substance. Spinoza’s views advocate a form of pantheism where everything experienced, be it through thought or extension, is a manifestation of the one essence, which is God. Put simply, the world is not created by God, it is God.

While Spinoza’s ideas address some of the problems with dualism, they raise some difficulties of their own. Firstly we have the problem of individuals and personal identity. Individuals clearly cannot be substances since they share attributes. Individuals then are modes in Spinoza’s interpretation and can only be understood as being ‘in’ something else. Spinoza developed a conception of individuality based upon the notion of conatus – the tendancy of complex structures such as living organisms to preserve their own integrity and wholeness. Thus we may speak of individual animals, birds and people but only of lumps of wax or piles of coal. Human beings, to Spinoza, thus represented the peak of individuality since they are able to know this conatus both under the aspect of extension (shared with other living beings) but also under the aspect of thought.

The most serious implication of this theory is concerned with human freedom of will. To Spinoza, every idea is the mental equivalent of a physical process and every physical process is an embodiment of an idea. Within a reasoned argument or mathematical proof the flow of ideas follows one to the other according to the principles of logic. Likewise, the ordered nature of the physical world is a consequence of predictive casual laws – an event happens not by chance but as a necessary consequence of all that has preceded it. This leads inexorably to a total determinism since everything is ultimately caused by God, whose essence embodies His own cause. This must be so, according to Spinoza, because either something has a cause within itself (and must therefore be God) or is caused by something else which itself must have a cause. If nothing except God can include its own cause, then human freedom must be an illusion and we have no choice over our actions.

It was to address this problem that Spinoza developed his theory of the ‘passions’ where he explained the role of emotion in a description of free will which he claimed is compatible with determinism. Emotion is experienced as a passive reaction to a cause outside oneself over which the individual has no control. Spinoza advances a theory that freedom in a certain restricted sense can be attained only through the intellect grasping the entirely of the whole which gives rise the to causes of the emotions. One must achieve freedom of the will then through gaining an ‘adequate conception’ of the emotions and their relationship to their cause. To Spinoza, the free man is the man who has gained adequate knowledge of and hence control of the passions.

How does Spinoza’s idea of substance accord with our current thinking in physics? There are many aspects which parallel the current quest to unify the fundamental forces (electromagnetic, string and weak nuclear and gravity) as aspects of a single reality. Quantum mechanics and general relativity have provided a series of separate unifications of previously separate concepts: matter and energy, time and space, waves and particles. The intellectual goal of the current century must be the synthesis of a quantum theory of gravity whereby all the laws of physics can be derived from a single underlying essence. This essence will likely be a form of field within which energy is quantised so as to give rise to the strange manifestations of wave-particle duality observed. At the same time the theory must account for the bending of space-time by matter through the gravitational force.

There are some striking similarities here with Spinoza’s work. All fundamental forces except gravity can be successfully accommodated within quantum field theory. Gravity and quantum mechanics then are different aspects under which reality is manifested. Similarly, particles such as electrons can be perceived either as waves or as particles depending upon the experimental conditions of the observer. In reality, electrons are neither classical waves or particles – these are just modes of their actual essence – a quantised field.

Another parallel is the relativistic concept of spacetime and Spinoza’s cosmic determinism. Physics views dimensional reality as a single spacetime which encapsulates both extension and eternity. Events then do not progress or ‘flow’ through time – they merely co-exist at different locations of a spacetime manifold. My world line contains all the events of my existence in a single object where ‘before’ and ‘after’ have exactly the same implications as ‘left’ and ‘right’. Since all events occur together there is no latitude for choice – my world line is complete and contains no points where I may select an alternative path. Relativity then implies a form of determinism which is entirely compatible with Spinoza’s divine substance which contains both infinite extension and infinite time.

While there are parallels here, Spinoza fails to provide a coherent unification of mind and extension other than somewhat elliptical claims that they are ‘separate aspects’ of a singular essence. He offers no insight into how mind supervenes on matter since, in Spinoza’s conception, there really is no interaction between the two and any requirement that they interact is unwarranted. When I have thought then I also have associated physical processes – but one does not have a causal explanation in the other. We are left then with the mystery of consciousness and its basis in the underlying substance of matter and energy.

In summary, Spinoza evades the key problems faced by Descartes by proposing a form of opportunistic dualism – thought and extension are separate and different and yet at the same time one and the same. Certainly the concept of a single underlying substance has many of the attributes of truth in that it is the simplest and best explanation and is in accordance with our experience of the nature of the physical world. Science has been consistent in generating theories which successively unify and simplify the nature of reality. This is certainly in agreement with Spinoza and sharply contradicts the pluralist viewpoint of Leibniz. However, Spinoza’s obscure treatment of the basis of free will and failure to provide an adequate account of mentality leaves open the way to a better explanation of reality.


1. Baruch Spinoza, Ethics, Part 1