Perhaps one of the greatest obstacles to modern readers of Spinoza Ethics is the language he uses. It is one which would be perhaps understandable to readers of his time, but has become pretty meaningless to us now. It is a language that has its roots in scholasticism, though, like Descartes, (who is the most important philosophical influence on Spinoza) everything he writes is a rejection of this tradition. Scholasticism obtains its language from Aristotle (or at least as he is handed down by the Islamic scholars to the West in the 9th century), so we first need to go back to this source.
Those of you who did the first year course on Greek philosophy might remember we briefly discussed Aristotle’s philosophy and especially his notion of ‘substance’, and this is where we need to start, since ‘substance’ in one of the most important words in Spinoza’s vocabulary. We are also going to use as our guide here the excellent book by Woolhouse, The Concept of Substance in Seventeenth Century Metaphysics (Woolhouse 1993, pp.14–27).
When we normally think of the word ‘substance’ in English, we associate it with the idea of matter. As for example, when we think of the question ‘what substance is this table made out of?’, we would probably respond by saying, ‘wood’ or ‘plastic’, corresponding to the material it was constructed from. This is not what Aristotle means by substance at all, and certainly not what Spinoza means by it. In fact Aristotle has a completely different word for matter in Greek, which is hyle. The word in Greek for substance is, on the contrary, ousia. Ousia is the 3rd personal singular feminine present participle of the Greek verb ‘being’. Now the grammar of this word is not particularly important for us, but what is important is that it has its origin in the verb ‘being’. Ousia is not the word for matter for Aristotle but for what is. Everything that is, is named by the word ousia, since everything that is must necessarily be; that is, must necessarily possess being, whether we’re talking about tables, galaxies or even ourselves. This notion of being, Aristotle says in the Metaphysics, is the proper subject matter of philosophy, and no other study. So the question we must ask ourselves is what did Aristotle think was the answer to the question what is being?
What is real for Aristotle are individual things like men, animals and plants and so on, and what is, is made up of these individual things. This seems to follow common sense, and it is clear those philosophers before Aristotle where not so ready to agree with common sense. Many of them tended to believe that there was a much greater reality behind the individual things we experience, which it is the task of philosophers to describe. Think, for example of the first Greek philosopher that we have any information about, Thales, who thought that every individual thing was in fact made of water, which was therefore the ultimate explanation and reality of the universe.
The best way to understand Aristotle’s idea of substance is to go back to his theory of predication. In fact we might say that it is this theory of predication which is the true source of his understanding of being: the way we understand being has its origin in the way we talk about the world. A substance for Aristotle is a subject of a predicate, but which at the same time is not a predicate of anything else. This is true definition of what we mean by an individual thing: it is independent of anything else. This notion of independence, as we shall see, is crucial to the meaning of substance, and is the key especially of understanding Spinoza’s use of the word. A substance is what undergoes change (it can have different predicates attached to it), but it itself remains the same, or holds onto its identity. Think of Socrates the man. He can be young or old, cold or warm, wise and ignorant, and so on. We can predicate all these different and opposite predicates of Socrates, but nonetheless it is still Socrates the individual (who is different from Peter and the chair over there) who we say these things of. Substance, then, has two very important parts of its definition: independence, and identity.
Now the question for Aristotle, as it is for every philosopher, is whether individual things are the ultimate substance or whether there is something greater than individual things, and which can explain them in a better way than they can explain themselves. This would mean that individual things would not be independent but would be dependent on something higher. In the same way that hot only makes sense predicated on some other individual thing, and can only have a meaning because of this; individual things would be, in fact, predicates of something else. This would mean, therefore, that there ‘substantialness’, in the Aristotelian sense of the word, would be an illusion. But it is precisely this kind of thinking he rejects. What is real are individual things, and it is they that undergo change and not something else. We tend to think there is some more ultimate reality because like Plato we confuse the definition of something with its reality – thus, because we notice there is something common between different horses, we make the mistake of thinking that there is some kind of ‘Horse’ which is the ultimate cause of them. Or we confuse substance with matter; that is to say, we think everything is the same because they are all made of the same kind of stuff. It is true that things are made of matter, and there might be some ultimate matter which is the explanation of all forms of matter (like atoms), but that is not enough to explain what something is for Aristotle. For Aristotle what something is made up of its matter and its form, and it is this form which is explained by substance. The form, therefore, tells us what the thing is and why it is what it is. Matter, alone, for Aristotle, cannot do this, for it just tells what is the same about everything, but not why this thing is the thing that it is and not any other.
The most important influence, as we have already indicated, on Spinoza is Descartes, who will use this Aristotelian vocabulary, but will give it a very different meaning. The two important characteristics, however, remain: independence and identity. Descartes writes as though he has escaped Scholastic philosophy, which has been the dead hand on scientific progress by retaining the Aristotelian view of nature, against the new mechanist theory of nature. But this is just propaganda, for he will still use their vocabulary, and in relation to the idea of God, there is much that is ‘scholastic’ in his thought. The most important influence is the very idea of God itself. For this is not something that would have been of concern for Aristotle, at least not as it is presented in theological thought. For Aristotle the universe is eternal, but for the Christian thinkers, such a view would deny creation; an idea which would have been utterly inconceivable to Aristotle. The idea of creation changes everything in the doctrine of substance, for the notion of independence belongs to its definition. If the universe is created by God, and it must be in Christianity, then everything that exists in creation must be dependent on Him. There, therefore, can only be one independent substance, which is God. Descartes, however, is not willing to go this far. Rather, he says, we can distinguish between two kinds of substance: infinite substance, which is God, and created substance, which is any individual thing which is dependent on God for its existence, but not anything else. We could say they have relative independence, and they correspond to what Aristotle defines as substance. A substance, just as in Aristotle, is everything which is conceived of through itself and not through some other kind of thing, and that which exists (apart from the fact that it is created) in its own right. A substance is therefore the subject of predication, of which we predicate qualities, properties and attributes to, and remains identical through change.
We say that created substance is similar to Aristotle’s notion of substance. It is similar in its definition (independence and identity), but not similar in what it describes. For substance describes individual things in Aristotle, tree, galaxies and you and me, but it does not do so for Descartes. To understand this difference, we are going to have to look at two other technical expressions, which are also fundamental for Spinoza: attributes and modes. Descartes’ philosophical system has three levels of reality: infinite substance, finite or created substance, and properties or qualities. We could see the relation between these levels as one of dependence: with infinite substance, created substance would not exist, and without created substance properties and qualities could not exist, for they always need to be properties or qualities of something. These properties or qualities of created substance Descartes calls modes. If modes are dependent on substance, then substance in itself cannot be a mode. We know substances, therefore, for Descartes through attributes, and there are two main attributes which explain all the possible modes that we know: extension and thought. The first explains objects in the world, and the second thoughts in our heads. These two are quite different, and this is why they are to be explained through two very different attributes, which cannot explain each other. A thought is not an object, and an object is not a thought. Attributes, therefore, have something in common with substances: they can only be conceived through themselves and not through something else – thus we can only understand the attribute extension through extension (length, breadth and shape – which can be understood mathematically) and not through anything else, whereas a mode must be understood through extension (heat is the motion of particles). In the same way a thought can only be understood through the attribute thought, and not through anything else, whereas any mode of thought (belief, love, desire and so on) must be understood through thought, since one cannot desire something, for example, which one cannot think. These principle attributes constitute the nature of substance for Descartes, and there must, therefore, be two kinds of substances, which explains his dualist metaphysics. Thus, whatever exists, substance, attribute, mode, must either be a body or thought, and cannot be anything else. He does not give a reason why there is only two kinds of substance, but only that there are only two.
How then is Descartes different from Aristotle? In terms of nature, the notion of individual substances disappears, such as trees, galaxies and human beings called Socrates. Rather, there is only one corporeal substance, of which these things are only modes. Thus, Descartes gets rid of Aristotle’s notion of forms, which explains why each thing is what it is. For Descartes this can be explained by the location, motion and rest of matter itself, and no appeal to any form is required. Individual human minds are, however, for Descartes, individual substances in the way that Aristotle would still talk of them. Anyone who thinks is an individual thinker, and cannot be the same as any other individual thinker – we do not have the same thoughts (this follows the rule that any substance must be independent).
How, then, does Spinoza’s thought fit within these two descriptions of substance by Aristotle and Descartes? First of all it follows the same definition of substance that it must be conceived in and through itself. Again this is what is meant by saying that substance must be independent. Also his notion of attribute appears to be the same as Descartes, in that it expresses the way that we perceive substance. We might ask ourselves, therefore, how an attribute comes to express substance. Why this attribute and not any other, for example? We have already seen that Descartes just says that there are two, but not why there are only two. Attributes are ways through which substance is understood. Now we really need to take care with our propositions here. For though Spinoza will agree that it is through attributes that we understand substance, he will argue further that substance is not only conceived through itself, but also in itself. What is the difference between conceiving substance through itself and in itself? Descartes collapses the real distinction between finite substance and its attributes (whilst making the latter dependent on God who is separate and transcendent) and this is why he can only conceive of two principle attributes. But for Spinoza, thought and extension are only the way that we perceive substance, but it in itself must have infinite attributes, since it must be infinite. If it were finite, then it would be limited by something outside of itself, and therefore it will fail the test of independence which is the definition of substance. There must, therefore, be only one substance, and not two kinds of substances, as Descartes argues. If can only do so because he holds onto the difference between creation and God, finite and infinite substance. For Spinoza, on the contrary, there is only one substance which is ‘God or Nature’.
Woolhouse, R.S., 1993. Descartes, Spinoza, Leibniz : the Concept of Substance in Seventeenth-Century Metaphysics, London; New York: Routledge.
 Later on it will be important to see whether Spinoza is doing this, and whether substance means matter for him, for it is clear that unlike Aristotle he thinks that there is only one substance.
 This does not mean that thought and extension is merely the appearance of substance, which is something different in itself. They are real distinctions.