17th Century Theories of Substance

In contemporary, everyday language, the word “substance” tends to be a generic term used to refer to various kinds ofmaterial stuff (“we need to clean this sticky substance off the floor”) or as an adjective referring to something’s mass, size,or importance (“that is a substantial bookcase”). In 17th century philosophical discussion, however, this term’s meaningis only tangentially related to our everyday use of the term. For 17th century philosophers the term is reserved for theultimate constituents of reality on which everything else depends. This article discusses the most important theories ofsubstance from the 17th century: those of Descartes, Spinoza, and Leibniz. Although these philosophers were highlyoriginal thinkers, they shared a basic conception of substance inherited from the scholastic-Aristotelian tradition fromwhich philosophical thinking was emerging. In a general sense each of these theories is a way of working out dualcommitments: a commitment to substance as an ultimate subject and a commitment to the existence of God as asubstance. In spite of these systematic similarities between the theories, they ultimately offer very different accounts ofthe nature of substance. Given the foundational role substance plays in the metaphysical schemes of these thinkers, itwill not be surprising to find that these theories of substance underlie dramatically different accounts of the nature andstructure of reality.

Table of Contents

1. 17th Century Theories of Substance: A Shared Background

2. Descartes

a. Descartes’ Account of Substance

b. What Substances are There?

c. Are Embodied Human Beings Substances?

d. How is Substance Independent?

e. How Many Material Substances?

3. Spinoza

a. Spinoza’s Account of Substance

b. What Substances are There?

c. Why doesn’t Spinoza Countenance Created Substance?

d. How Can a Substance Have More than One Attribute?

e. An Extended and Indivisible Substance?

4. Leibniz

a. Leibniz’s Account of Substances

b. What Substances are There?

c. Experience and Reality

d. What is Wrong with Composite Beings?

e. Leibniz and Spinoza

5. 17th Century Theories of Substance in Perspective

6. References and Further Reading

a. Primary Texts in English

b. Secondary Texts

1. 17th Century Theories of Substance: A Shared Background

In thinking about 17th century accounts of substance we need to keep in mind that a concern with substance and itsnature was nothing new to the period. In fact, philosophical thinking about the nature of substance stretches all the wayback to ancient Greece. While the new philosophers of the 17th century were keen to make a break with the past and totackle philosophical and scientific problems from new foundations, their views did not develop in an intellectual vacuum. Indeed, the scholastic-Aristotelian tradition of the day informed their thinking about substance in a number of ways, andcontributed to a number of commonalities in their thought. Before looking at specific theories of substance, it is importantto note four commonalities in particular.

Substance, Mode, Inherence

For the philosophers we will discuss, at the very deepest level the universe contains only two kinds or categories ofentity: substances and modes. Generally speaking, modes are ways that things are; thus shape (for example being arectangle), color (for example redness), and size (for example length) are paradigm modes. As a way a thing is, a modestands in a special relationship with that of which it is a way. Following a tradition reaching back to Aristotle’s Categories,modes are said to exist in, or inhere in, a subject. Similarly, a subject is said to have or bear modes. Thus we might saythat a door is the subject in which the mode of rectangularity inheres. One mode might exist in another mode (a colormight have a particular hue, for example), but ultimately all modes exist in something which is not itself a mode, that is,in a substance. A substance, then, is an ultimate subject.

Independence and Priority

The new philosophers of the 17th century follow tradition in associating inherence with dependence. They all agree thatthe existence of a mode is dependent in a way that the existence of a substance is not. The idea is that modes, as theways that things are, depend for their existence on that of which they are modes, e.g. there is no mode of ‘being 8’0 long’without there being a subject that is 8’0 long. Put otherwise, the view is that the existence of a mode ultimately requiresor presupposes the existence of a substance. This point is sometimes put by saying that substances, as subjects, aremetaphysically prior to modes.

Degrees of Reality

In contrast to contemporary philosophers, most 17th century philosophers held that reality comes in degrees—that somethings that exist are more or less real than other things that exist. At least part of what dictates a being’s reality,according to these philosophers, is the extent to which its existence is dependent on other things: the less dependent athing is on other things for its existence, the more real it is. Given that there are only substances and modes, and thatmodes depend on substances for their existence, it follows that substances are the most real constituents of reality.

God Exists and is a Substance

Furthermore, each of the philosophers we will discuss maintains (and offer arguments on behalf of the claim) thatGod exists, and that God’s existence is absolutely independent. It is not surprising then, given the above, that each ofthese philosophers holds that God is a substance par excellence.

2. Descartes

Descartes’ philosophical system, including his account of substance was extremely influential during the 17th century. For more details see the IEP entry René Descartes: Overview. Unlike Spinoza and Leibniz, however, Descartes’ theoryof substance was not the centerpiece of his philosophical system. Nonetheless, Descartes offered a novel theory ofsubstance which diverged in important ways from the Scholastic-Aristotelian tradition.

a. Descartes’ Account of Substance

It is sometimes said that Descartes gives two different definitions of substance, and indeed in the Principles and SecondReplies he defines substance in distinct ways. We should not, however, see this as evidence that Descartes changed hismind. On the contrary, it is clear that for Descartes these definitions express two sides of a unified account of substance.

Let us begin with the definition he offers in his Principles of Philosophy (I.51-52). There he defines ‘substance’ in termsof independence. He begins by making clear that there are really two different philosophical senses of the term(corresponding to two degrees of independence). For reasons that will become clear in a moment, let us distinguish thetwo senses by calling one Substance and the other Created Substance. Descartes’ definitions can be paraphrased asfollows:

Substance: A thing whose existence is dependent on no other thing.

Created Substance: A thing whose existence is dependent on nothing other than God.

Strictly speaking, for Descartes there is only one Substance (as opposed to Created Substance), since there is only onething whose existence is independent of all other things: God. However, within the universe that God has created thereare entities the existence of which depends only on God. These lesser substances are the ultimate constituents of thecreated world.

The definition of substance that Descartes offers in the Second Replies (and elsewhere), ignores the distinction betweenGod and creation and defines substance in a much more traditional way, claiming that a substance is a subject that has orbears modes, but is not itself a mode of anything else. This fits right in with his other comments about substance in thePrinciples. Thus, he tells us that each created substance has exactly one attribute (Principles I. 53). An attribute of asubstance, Descartes explains, is its “principle property which constitutes its nature and essence, and to which all itsother properties are referred” (Ibid.). A substance’s attribute, consequently, dictates its kind since attributes“constitute” a substance’s nature and all and only those things of the same nature are of the same kind. Moreover, inclaiming that all a substance’s properties are referred through the substance’s attribute, Descartes is claiming that asubstance’s attribute dictates the properties that a substance may have.

Descartes specifies two attributes: thought and extension. Consequently, there are at least two kinds of createdsubstance—extended substances and thinking substances. By ‘extension’ Descartes just means having length, breadth,and depth. More colloquially we might say that to be extended is just to take up space or to have volume. Whereas by‘thinking substance’ Descartes just means ‘mind’. Although Descartes only ever discusses these two attributes, he neverexplicitly rules out the possibility of other attributes. Nevertheless, the tradition has interpreted Descartes as holdingthat there are only two kinds of created substance and it is for this reason that Descartes is often called a substancedualist.

With this specification in hand we are in a better position to understand what Descartes means when he says that all asubstance’s properties are referred through the substance’s attribute or “principle property.” Consider an extendedsubstance, say, a particular rock. Among this rock’s properties are shape and size; but having these propertiespresupposes the property of extension. Put otherwise, something cannot have a shape or a size without also beingextended. Furthermore, the properties that the rock may have are limited to modifications of extension—a rock cannothave the property of experiencing pain for example, since the property of experiencing pain is not a way of beingextended. In general, we can say that for Descartes i) the attribute of a substance is its most general property, and thatii) every other property of a substance is merely a specification of, way of being, or mode of that attribute.

b. What Substances are There?

Given this account of the nature of substance, what substances exist? Descartes famously argues in Meditation Six thathuman minds and bodies are really distinct—that is, that they are each substances. Indeed, every individualconsciousness or mind is a thinking substance. Furthermore Descartes treats bodies, including the objects of oureveryday experience (chairs, trees, spoons, etc.) as extended substances. This makes sense: extension is an attribute ofsubstance, so it would seem to follow that anything that is extended (has the attribute of extension) is itself a substance. Moreover the parts of extended substances, as themselves extended, would seem to be extended substances forDescartes (see Principles I. 60). Given that Descartes thinks that matter is infinitely divisible (Principles II. 20)—thateach part of matter is itself extended all the way down—it follows that there are an infinite number of extendedsubstances.

We are thus left with the following picture of reality. The most real thing is God on which all other things depend. However, within the created realm there are entities that are independent of everything besides God. These are thecreated substances. Created substances come in two kinds—extended substances and minds, and there is a plurality ofboth.

This brief summary of Descartes’ account of substance raises a number of deeper questions and controversies. Onecentral question that naturally arises is why Descartes thinks that extension and thought are the most general propertiesof substances. For a detailed discussion of Descartes’ reasons see the IEP entry René Descartes: The Mind-BodyDistinction. This entry will briefly consider the role of embodied human beings in Descartes metaphysics, what Descartesmeans in calling substances independent, and a related controversy concerning the number of material substances towhich Descartes is entitled.

c. Are Embodied Human Beings Substances?

Embodied human beings fit uneasily into Descartes’ metaphysics. As embodied, humans are composite beings; anembodied human being consists of a mental substance (our mind) and a physical one (our body), for Descartes. Descartesthinks that this composite being is, however, something over and above a mere aggregation. He writes in Mediation Six:“Nature also teaches me…that I am not merely present in my body as a sailor is present in a ship, but that I am veryclosely joined and, as it were, intermingled with it, so that I and the body form a unit” (my italics). In general, it is clearthat Descartes thinks that embodied humans are exceptional beings in some regard, but how we should understand thismind/body union and its place in Descartes’ metaphysics has been a matter of some controversy among scholars. One ofthe more prominent disputes has been between those scholars who read Descartes as holding that embodied humanbeings are a distinct kind of created substance, and those scholars who do not. The former see Descartes as a substancetrialist, whereas the latter read him along traditional lines as a substance dualist. For trialist readings see Hoffman 1986and Skirry 2005: Chapter 4). For recent defenses of substance dualism against trialist interpretations see Kaufman2008 and Zaldivar 2011.

d. How is Substance Independent?

As we have seen, Descartes defines substance in terms of independence. This, however, is only a very general claim. Inorder to better understand Descartes’ account of substance we need to have a better idea of the way in which substancesare independent. On one hand, in his thinking about substance Descartes is working with the traditional conception ofindependence according to which a substance’s existence is independent in a way that a mode’s existence is not, sincesubstances are ultimate subjects. Accordingly, let us say that substances are subject-independent. On the other hand, inhis account of substance Descartes is also working with a causal sense of independence. After all, the reason that God isthe only Substance (as opposed to Created Substance) is that all other things “can exist only with the help of God’sconcurrence” (Principles I.51), and Descartes understands this as the causal claim that all other things are God’s creationand require his continual conservation. Consequently scholars have seen Descartes as holding that in general i) God isboth causally and subjectively independent (God is not, after all, a mode of anything else), ii) created substances arecausally independent of everything but God and subjectively independent, and iii) modes are both causally andsubjectively dependent in that they both depend on God’s continual conservation and on created substances as subjects.(See for example, Markie 1994: 69; Rodriguez-Pereyra 2008: 79-80)

e. How Many Material Substances?

That created substances are causally independent of everything but God suggests a startling conclusion—that despitewhat Descartes seems to say, bodies are not material substances, since they are not sufficiently independent. Bodies arecausally dependent on other bodies in a host of different ways. For example, bodies come to be and are destroyed byother bodies: a person is the product of their parents and could die as the result of getting hit by a car. Indeed, accordingto one scholarly tradition, there is only one material thing that satisfies Descartes’ definition of created substance—thematerial universe as a whole (see for example, Cottingham 1986: 84-85). Again, following tradition we can call this viewthe Monist Interpretation, and the opposing view that there are many material substances, the Pluralist Interpretation(for a distinct view see Woolhouse 1993: 22-23). It would appear, then, that there is philosophical evidence of Monism; inother words, it would seem that Descartes’ views about created substance commit him to thinking there can be only onematerial substance. Proponents of this interpretation claim that there is textual evidence as well, pointing to a passage inthe Synopsis to the Meditations. There Descartes writes:

[W]e need to recognize that body, taken in the general sense, is a substance, so that it too never perishes. But thehuman body, in so far as it differs from other bodies, is simply made up of a certain configuration of limbs and otheraccidents of this sort; whereas the human mind is not made up of any accidents in this way, but is a pure substance.

Monists read ‘body, taken in the general sense’ as referring to the material universe as a whole. Consequently, they seethis passage as claiming that the material universe is a substance, but that the human body is not—since it is made up ona configuration of limbs and accidents. Assuming the monists are right, two questions immediately arise. First, if bodiesare not substances, then what are they? Monists typically claim that bodies are modes. This makes sense: if bodies arenot substances, they must be modes, given Descartes’ ontology. Second, if Descartes does not think that bodies are

substances, why does he so often talk as if they are? Monists answer that Descartes is speaking loosely in these contextsusing the term ‘substance’ in a secondary or derivative sense of the term.

Pluralists have objected on a number of grounds. First, pluralists have challenged the monist’s textual evidence, offeringalternative readings of the Synopsis. Second, they have challenged the motivation of monism, pointing out that themonist interpretation requires a very strong conception of causal independence, and that it just isn’t clear that this isDescartes’ view. Third, pluralists note that although Descartes writes of bodies as substances on numerous occasions, henever clearly refers to them as modes. Last, pluralists have denied that Descartes could have held that bodies are modesnoting that for Descartes i) parts of things are not modes of them and ii) bodies are parts of the material universe. Hoffman 1986 briefly raises each of these objections. For more lengthy discussions see Skirry 2005: Chapter 3 andSlowik 2001.

3. Spinoza

Spinoza’s most important work is his Ethics Demonstrated in Geometric Order—henceforth the Ethics. Spinoza workedon the text throughout the 1660s and 70s. By this time Descartes’ philosophy had become widely read and indeedSpinoza’s thinking was heavily influenced by it—including his account of substance. Nevertheless, Spinoza’s accountdiverges in important ways and leads to a radically different picture of the world.

a. Spinoza’s Account of Substance

Spinoza offers a definition of substance on the very first page of the Ethics. He writes: “By substance I understand whatis in itself and is conceived through itself… “ (E1d3). Spinoza follows Descartes (and the tradition) in defining substance as“in itself” or as an ultimate subject. Correspondingly, he follows the tradition in defining ‘mode’ as that which is had orborne by another; as Spinoza puts it a mode is “that which is in another…” (E1d5). For a discussion of the scholastic-Aristotelian roots of Spinoza’s definition see Carriero 1995. Spinoza also follows Descartes in thinking that i) attributesare the principle properties of substance, ii) among those attributes are thought and extension, iii) all other properties ofa substance are referred through, or are ways of being, that attribute, and iv) God exists and is a substance. Here theagreement ends.

The first obvious divergence from Descartes is found at E1P5. For Descartes there are many extended substances (atleast on the pluralist interpretation) and many minds. Spinoza, however, thinks this is dead wrong. At E1P5 Spinozaargues that substance is unique in its kind—there can be only one substance per attribute. This fact about substance (incombination with a number of other metaphysical theses) has far-reaching consequences for his account of substance.

It follows, Spinoza argues at E1P6, that to be a substance is to be causally isolated, on the grounds that i) there is only onesubstance per kind or attribute and ii) causal relations can obtain only between things of the same kind. Causal isolationdoes not, however, entail causal impotence. An existing substance must have a cause in some sense, but as causallyisolated its cause cannot lie in anything outside itself. Spinoza concludes that substance “will be the cause of itself…itpertains to the nature of a substance to exist” (E1P7). Not only is a substance the cause of itself, but Spinoza later tells usthat it is the immanent cause of everything that is in it (E1P18). Spinoza continues, in E1P8, by claiming that “everysubstance is necessarily infinite.” In general Spinoza argues that if there is only one substance per attribute, thensubstance cannot be limited since limitation is a causal notion and substances are causally isolated. Last, Spinoza makesthe case that substances are indivisible. He argues in E1P12-13 that if substance were divisible, it would be divisibleeither into parts of the same nature or parts of a different nature. If the former, then there would be more than onesubstance of the same nature which is ruled out by E1P5. If the latter, then the substance could cease to exist which isruled out by E1P7; consequently substance cannot be divided.

b. What Substances are There?

Given this account of the nature of substance, what substances exist? From what has been said so far in the Ethics itwould be reasonable to suppose that, for Spinoza, reality consists of the following substances: God, one extendedsubstance, one thinking substance, and one substance for every further attribute, should there be any. As it turns out,however, this is only partially right. It is true that Spinoza ultimately holds that God exists, that there is one extendedsubstance, and one thinking substance. However, Spinoza denies that these are different substances. The one thinkingsubstance is numerically identical to the one extended substance which is numerically identical to God. Put otherwise,there is only one substance, God, and that substance is both extended and thinking.

Spinoza’s official argument for this conclusion is at E1P14. He argues as follows: God exists (which was proven at E1P11). Given that God is defined as a being that possesses all the attributes (E1d6) and that there is only one substance perattribute (E1P5), it follows that God is the only substance. For a detailed discussion of this argument see the IEP entrySpinoza: Metaphysics.

Given that God is the only substance and Spinoza’s substance/mode ontology, it follows that the material objects of ourexperience are not independently existing substances, but instead are modes of the one extended substance. So too,minds which Descartes had thought of as thinking substances are, according to Spinoza, modes of the attribute of thought.

We are thus left with the following picture of reality. Like Descartes, Spinoza holds that the most real thing is God onwhich all other things depend. However, there are no created substances. God as the one substance has all theattributes, and consequently is both an extended substance and a thinking one. What Descartes had taken for createdsubstances are actually modes of God. Nevertheless, Spinoza agrees with Descartes that the contents of reality come intwo kinds—modes of extension and modes of thought, and there is a plurality of both.

This account of the nature of substance yields a very different picture of the metaphysical structure of the world fromDescartes (and from common sense). This entry will focus on three questions in particular: i) why doesn’t Spinoza acceptcreated substances, ii) how can a substance have more than one attribute, and iii) how can a substance be indivisible as

Spinoza suggests?

c. Why doesn’t Spinoza Countenance Created Substance?

Spinoza will not countenance Descartes’ distinction between Substance and Created Substance for a number of reasons. First, created substances are the causal products of God. However, substances are causally isolated, and so even if therewere multiple substances, one could not be the causal product of the other. Second, as we have seen Descartes holds thatdespite their causal dependence on God, finite minds and bodies warrant the name ‘substance’ at least partially becausesuch beings are ultimate subjects. Spinoza agrees that being an ultimate subject is an essential part of being a substance;the problem is that finite bodies and minds are not ultimate subjects. Spinoza’s official grounds for this thesis are found inthe arguments for E1P4 and 5. In general, Spinoza claims that what is distinctive of substances as ultimate subjects isthat they can be individuated by attribute alone. According to Spinoza there are only two kinds of mark by which entitiesmight be individuated—by attribute and by mode. Substances as ultimate subjects cannot be individuated by mode,since subjects are metaphysically prior to modes. Two finite bodies, for example, are not individuated by attribute (sincethey are both extended) and so cannot be substances.

d. How Can a Substance Have More than One Attribute?

As we’ve seen, for Descartes each substance has one—and only one—attribute. Spinoza’s argument for substancemonism, on the other hand, claims that there is a substance that possesses all the attributes. Spinoza justifies this movedefensively; at E1P10s Spinoza claims that nothing we know about the attributes entails that they must belong todifferent substances, and consequently there is nothing illegitimate about claiming that a substance may have more thanone attribute. Although this is Spinoza’s stated defense, a number of scholars have claimed that Spinoza has thephilosophical resources to make a much stronger argument. Specifically, they claim he has a positive case that, in fact, asubstance possessing anything less than all the attributes (and hence, just one) is impossible. In brief Lin 2007 asks us tosuppose that Spinoza is wrong, and that it is possible for there to be a substance that has fewer than all of the attributes(but at least one). Spinoza is a strong proponent of the Principle of Sufficient Reason (see for example, E1P8s2) accordingto which there is an explanation for every fact. Given the PSR it follows that there is an explanation of why the substancein question fails to have all the attributes. However, any such explanation will have to appeal to the substance’s existingattribute (or attributes). Attributes are conceptually independent however, and consequently one cannot appeal to anexisting attribute to explain the absence of another. For a different but closely related version of this argument see DellaRocca 2002.

e. An Extended and Indivisible Substance?

Unlike Descartes, Spinoza holds that substance is indivisible, and this raises a number of questions about the consistencyof Spinoza’s account of substance. For example, how is substance’s indivisibility consistent with Spinoza’s claims that (i)substance has many attributes which constitute its essence and (ii) that substance is extended? For a discussion of i) seethe IEP entry Spinoza: Metaphysics. Here the focus is on ii).

Spinoza’s extended substance, or God considered under the attribute of extension, is normally understood asencompassing the whole of extended reality (though for an alternative see Woolhouse 1990). According to a philosophicaltradition going back at least to Plato’s Phaedo, to be extended or corporeal is to have parts, to be divisible, and hence tobe corruptible. Spinoza, however, holds that “it pertains to the nature of substance to exist.” Consequently, it wouldseem to follow that Spinoza cannot consistently hold that substance is extended. Spinoza was well aware of this argumentand his official rejoinder is found in E1P15s. The problem with the argument is that it is “founded only on [the]supposition that corporeal substance is composed of parts.” On its face, this is a confusing claim—if extended or corporealsubstance just is the whole of extended reality, it surely has parts. For example, there is the part of extension whichconstitutes an individual human body, a part which constitutes the Atlantic Ocean, a part that constitutes Earth, etc. Despite his wording, Spinoza is not denying that extended substance has parts in every sense of the term. Rather,Spinoza is especially concerned to counter the idea that his extended substance is a composite substance, built out ofparts which are themselves substances, and into which it might be divided or resolved. This makes sense, since a) it isnot having parts that is the problem, but being corruptible, and b) this account of extended substance as divisible intofurther extended substances is just what Descartes (one of the main influences on Spinoza’s thought) seems to have held.

Spinoza makes his case in two ways in E1P15s. First, Spinoza points us back to the arguments at E1P12 and 13 for theindivisibility of substance. Second Spinoza offers a new argument that focuses specifically on extended substance, onethat, interestingly, does not presuppose the prior apparatus of the Ethics. In putting aside his own previous conclusions,Spinoza’s apparent goal is to show that a view like Descartes’ according to which any extended substance has parts whichare themselves extended substances, fails on its own terms. In general, he argues as follows. Consider an extendedsubstance, say a wheel of cheese. If the parts of this wheel are themselves extended substances, then it is—at least inprinciple—possible for one or more of the parts to be annihilated without any consequence for the other parts. The ideahere is that because substances are independent subjects, the annihilation of one subject cannot have any consequencefor the others. Suppose then that the middle of our wheel of cheese is annihilated; we are thus left with a “donut” ofcheese. The problem with this is that the hole in the cheese is measurable—it has a diameter, a circumference, etc. Inshort, it is extended. However, we have supposed that the extended substance—the subject of the extension—in themiddle was destroyed. We are thus left with an instance of attribute, extension, without a substance as its subject—animpossibility by both Descartes’ and Spinoza’s standards. For detailed discussions of this argument see Huenemann 1997and Robinson 2009.

4. Leibniz

Leibniz’s views were informed by the accounts of both Descartes and Spinoza. In fact, Leibniz corresponded with Spinozaduring the early 1670s and briefly visited with Spinoza in 1676. Unlike Spinoza, Leibniz did not write a singleauthoritative account of his metaphysical system. Not only that, but his metaphysical views changed in significant ways

over his lifetime. Nevertheless, it is possible to identify a core account of the nature of substance that runs throughout hismiddle to later works (from the Discourse on Metaphysics of 1686 through the Monadology of 1714).

a. Leibniz’s Account of Substances

Substances are independent and are ultimate subjects.

Like Descartes, Leibniz thinks that God is the only absolutely independent thing, and that there are, in addition, createdsubstances which are “like a world apart, independent of all other things, except for God” (Discourse on Metaphysics§8). Second, Leibniz explicitly agrees with Descartes, Spinoza, and the tradition in maintaining that substances are theultimate bearers of modes or properties. He writes “when several predicates are attributed to a single subject and thissubject is attributed to no others, it is called an individual substance” (Ibid.).

Substances are unities.

To be a unity for Leibniz is to be simple and without parts, and so the ultimate constituents of reality are not composite oraggregative beings. That substances are simple has metaphysically significant consequences; Leibniz infers in thePrinciples of Nature and Grace and elsewhere that “Since the monads have no parts, they can neither be formed nordestroyed. They can neither begin nor end naturally, and consequently they last as long as the universe.” A being comesto be naturally only as the result of a composition; an entity is destroyed naturally only through dissolution or corruption. Thus only composite entities are naturally generable or destructible. Leibniz emphasizes, however, that substances’unity and consequent simplicity is entirely consistent with the possession of and changes in modes or properties.

Substances are active.

To say that a substance is active is to say not only that it is causally efficacious, but that it is the ultimate (created) sourceof its own actions. Thus he writes, “every substance has a perfect spontaneity…that everything that happens to it is aconsequence of its idea or of its being, and that nothing determines it, except God alone” (DM §32). Substances, in somesense, have their entire history written into their very nature. The history of each substance unfolds successively, eachstate causally following from the previous state according to laws. From this it follows that if we had perfect knowledge ofa substance’s state at a time and of the laws of causal succession, we could foresee the entire life of the substance. AsLeibniz elegantly put the point in the Principles of Nature and Grace “the present is pregnant with the future; the futurecan be read in the past; the distant is expressed in the proximate.”

Substances are causally isolated.

Like Spinoza, Leibniz holds both that substances are causally efficacious, and that their efficacy does not extend to othersubstances. In other words, although there is intra-substantial causation (insofar as substances cause their own states),there is no inter-substantial causation. Leibniz offers a number of different arguments for this claim. On some occasionshe argues that causal isolation follows from the nature of substance. If a state of a substance could be the causal effect ofsome other substance, then a substance’s spontaneity and independence would be compromised. Elsewhere he arguesthat inter-substantial causation is itself impossible, claiming that the only way that one substance might cause another isthrough the actual transfer of accidents or properties. Thus Leibniz famously writes that substances “have no windowsthrough which something can enter or leave. Accidents cannot be detached, nor can they go about outside of substances”(Monadology §7). For a more detailed discussion of Leibniz’s views of causation see the IEP entry Leibniz: Causation.

b. What Substances are There?

Although Leibniz agrees with Descartes that God is an infinite substance which created and conserves the finite world, hedisagrees about the fundamental constituents of this world. For Descartes there are fundamentally two kinds of finitesubstance—thinking substances or minds and extended substances or bodies. Leibniz disagrees; according to Leibniz(and this is especially clear in the later works) there are no extended substances. Nothing extended can be a substancesince nothing that is extended is a unity. To be extended is to be actually divided into parts, according to Leibniz, andconsequently to be an aggregate. The ultimate created substances, for Leibniz, are much more like Cartesian thinkingsubstances, and indeed Leibniz refers to simple substances as “minds” or “souls.” This terminology can be confusing, andit is important to be clear that in using these terms Leibniz is not thereby claiming that all simple substances areindividual human consciousnesses (although human consciousnesses are simple substances for Leibniz). Rather, there isa whole spectrum of simple substances of which human minds are a particularly sophisticated example.

We are thus left with the following picture of reality. God exists and is responsible for creating and continually conservingeverything else. The ultimate constituents of reality are monads which are indivisible and unextended minds or mind-like substances. Although monads are causally isolated, they have properties or qualities that continually change, andthese changes are dictated by the monad’s nature itself. Leibniz’s account of substance and his metaphysics in general,raise a number of questions. This article will take up three in particular. First, Leibniz’s account of substance yields (inconjunction with a number of other metaphysical commitments) a picture of reality that diverges in significant ways bothfrom common sense and from Descartes and Spinoza. How does our experience of an extended world of causalinteraction fit into Leibniz’s metaphysical picture? Second, that substances are unities is a crucial feature of Leibniz’saccount, and it is important to consider why Leibniz is so opposed to composite substances. Last, Spinoza and Leibnizoffer very similar accounts of substance, yet end up with very different metaphysical pictures, and so this article willconsider where Leibniz’s account diverges from Spinoza’s.

c. Experience and Reality

How does the world of our experience fit into Leibniz’s account of reality? Our everyday experience is of extendedobjects causally interacting, but for Leibniz at the fundamental level there is no inter-substantial causation and there areno extended substances. How, then, is the world of our experience related to the world as it really is?

Let us begin with the apparent causal relations between things. Recall that, for Leibniz, monads are active andspontaneous. Each individual human mind is a monad, and this means that all of a human’s experiences—including theirsensations of the world—are the effects of their own previous states. For example, a person’s sensation of a book’s beingon the desk is not caused by the book (or the light bouncing off the book, entering the eye,…etc.) but is rather aprogression in the unfolding of the history written into the person’s nature. Although a monad’s life originates from itsnature alone, God has created the world so that the lives of created monads perfectly correspond. Leibniz writes in ANew System of Nature,

God originally created the soul (and any other real unity) in such a way that everything must arise for it from its owndepths…yet with a perfect conformity relative to external things…There will be a perfect agreement among all thesesubstances, producing the same effect that would be noticed if they communicated through the transmission ofspecies or qualities, as the common philosophers imagine they do.

Thus, when Katie walks around the corner and sees Beatrice, and Beatrice sees Katie, they do so because it was writteninto Katie’s very nature that she would see Beatrice, and into Beatrice’s nature that she would see Katie. This is Leibniz’sfamous doctrine of pre-established harmony. For more see the IEP entry Leibniz: Metaphysics.

How does our experience of an extended world of bodies arise? To start, Leibniz certainly doesn’t think that bodies arebuilt out of, or are composites of, monads. Thus he writes in his Notes on Comments by Michel Angelo Fardella, “just asa point is not a part of a line…so also a soul is not a part of matter.” Instead in many cases Leibniz characterizes bodies asphenomena or appearances. He writes in an oft-cited passage to DeVolder:

[M]atter and motion are not substances or things as much as they are the phenomena of perceivers, the reality ofwhich is situated in the harmony of the perceivers with themselves (at different times) and with other perceivers.

Leibniz seems to be saying here and elsewhere that bodies are merely appearances (albeit shared appearances) that donot correspond to any mind-independent reality, and indeed a number of scholars have claimed that this is Leibniz’sconsidered view (see for example, Loeb 1981: 299-309). In other texts however Leibniz claims that bodies result from,or are founded in, aggregates of monads, and this suggests that bodies are something over and above the mereperceptions of monads. In general, scholars have offered interpretations that attempt to accommodate both sets of textsand which see bodies as being aggregates of monads that are perceived as being extended. There is a great deal ofdebate, however, about how such aggregates might ultimately be related to bodies and their perception (for one accountsee Rutherford 1995b: 143-153).

d. What is Wrong with Composite Beings?

Leibniz thinks composite beings are excluded as possible substances on a number of grounds. First, no composite is (orcan be) a unity, since according to Leibniz there is no way that two or more entities might be united into a single one. Hefamously illustrates this claim by appealing to two diamonds. He writes in his Letters to Arnauld: “One could impose thesame collective name for the two…although they are far part from one another; but one would not say that these twodiamonds constitute a substance…Even if they were brought nearer together and made to touch, they would not besubstantially united to any greater extent… contact, common motion, and participation in a common plan have no effecton substantial unity.” In general, there is no relation that two or more entities might be brought into that would unifythem into a single being.

A second and perhaps even deeper problem with composites is that according to Leibniz they cannot be ultimate subjects.He writes, again in the Letters to Arnauld, “It also seems that what constitutes the essence of a being by aggregation isonly a mode of things of which it is composed. For example, what constitutes the essence of an army is only a mode of themen who compose it.” Leibniz’s claim is that no aggregate is a substance because aggregates are modes or states of theirparts, and no mode is an ultimate subject. This leaves us with a question, however: why does Leibniz think thataggregates are mere modes or states of their parts? In his influential book R.C. Sleigh (1990: 123-124) makes the casethat Leibniz’s grounds for thinking aggregates are modes is that aggregates are semantically and ontologicallydispensable. That is, everything that is true of an aggregate can be expressed by attributing various modes to the parts,all without appealing to the aggregate itself. This tells us that that all of an aggregate’s purported modes are in factmodes of the parts, and that consequently the aggregate is not an ultimate subject. Given a substance/mode ontology, itfollows that to the extent that aggregates exist, they must be modes.

e. Leibniz and Spinoza

Although Spinoza and Leibniz offer very different pictures of the structure of reality, their respective accounts ofsubstance overlap in important ways: both agree that to be a substance is to be at least i) an ultimate subject, ii) causallyisolated but causally efficacious, and iii) indivisible. Indeed, a number of scholars have suggested that Leibniz brieflyadopted or was at least tempted by a Spinozistic metaphysics early in his philosophical career (see for example, thediscussion in Adams 1994: 123-130). Even later in life Leibniz seems to have held Spinoza’s views in high regard sayingin a Letter to Louis Bourguet that “[A]ccording to Spinoza…there is only one substance. He would be right if there wereno monads.” Given this it is worth considering where Leibniz breaks with Spinoza and why.

Although they differ in a number of important ways, perhaps the most prominent difference between the metaphysics ofSpinoza and Leibniz is that Leibniz holds that reality is split into two: God and creation. God is a substance and Heproduces finite substances—created monads. This signals a break from Spinoza in at least two significant ways. First, itmeans that Leibniz’s agreement with Spinoza about the causal isolation of substances applies only to created substances;although for Leibniz God is a substance, He is not causally isolated. Recall that at least one of Leibniz’s reasons fordenying inter-substantial causation is that it would require the actual transfer of properties or accidents, and that such atransfer is impossible. Jolley (2005) makes the case that, for Leibniz, God’s causal activity is of a different kind. Goddoes not produce effects in a metaphysically intolerable way, and consequently, God need not be causally isolated.

Second, Leibniz holds, in contrast to Spinoza, that created substances are ultimate subjects. Leibniz is very explicit about

his objection to Spinoza on this score. Although he agrees that substances require individuation, he holds that Spinoza’sproof at E1P5 that there can be only one substance per nature or attribute is unsound. Furthermore Leibniz holds thatMonads can be individuated, ultimately claiming in the Monadology that “Monads…are…differentiated by the degrees oftheir distinct perceptions.”

5. 17th Century Theories of Substance in Perspective

Looking back we might see Descartes, but especially Spinoza and Leibniz, as working through the metaphysicalconsequences of holding that substances are ultimate subjects. More generally, we can see these theories of substance asdifferent ways of trying to reconcile the notion of substance as an ultimate subject with a commitment to God’s existenceand independence.

Epistemological considerations led prominent late 17th and 18th century philosophers to abandon such questions, and togive substance a much more modest position in their metaphysical systems. John Locke, for example, holds that thereare substances and that they are ultimate subjects, but is wary of drawing any further conclusions. As Locke famouslyclaims, “if any one will examine himself concerning his Notion of pure Substance in general, he will find he has no otherIdea of it at all, but only a Supposition of he knows not what support of such Qualities…commonly called Accidents” (EHU2.23.2). David Hume goes further claiming that it is not within out power to know the ultimate structure of reality, andthat further that our idea of a substance as a subject is merely the result of our imagination: “the imagination is apt tofeign something unknown and invisible, which it supposes to continue the same under all these variations; and thisunintelligible something it calls a substance” (Treatise 1.4.3). Humean skepticism about substance (and aboutmetaphysics more generally) survives in one form or another to the present day.

Of course not everyone agrees with this tradition, and the nature of substance has been a question that manycontemporary philosophers have taken up—albeit from different starting points than Descartes, Spinoza, and Leibniz. Unlike the 17th century, in contemporary philosophical use the term ‘substance’ is not necessarily intended to refer to theultimate constituents of reality (although it may). Rather the term is usually taken to refer to what are sometimes called“concrete particulars”, that is, to individual material things or objects. Furthermore, among contemporary philosophersthere is nothing like the consensus that we find among the 17th century philosophers regarding ontology, dependence,reality, and God. Thus, it is commonly held that there are categories of reality beyond substance and mode (orproperty), perhaps most prominently events or processes. Many philosophers have questioned both the relation ofinherence and the connection between inherence and ontological dependence (bundle-theories of substance, for example,deny that substances are subjects at all—they are merely bundles or collections of properties). Furthermore, mostcontemporary philosophers deny that it makes sense to talk about degrees of reality: things are either real or not. Last,and perhaps most obviously, contemporary philosophers no longer agree that God exists and is a substance. For acontemporary effort to offer an account of substance that is in the spirit of 17th century discussions see Hoffman andRosenkrantz 1997.

6. References and Further Reading

a. Primary Texts in English

Descartes

John Cottingham, Robert Stoothoff, Dugald Murdoch, and Anthony Kenny ed. and trans. The Philosophical Writings ofDescartes, 3 vols., Cambridge: Cambridge University Press, 1984-1991.

This is the standard English edition of Descartes’ work.

Spinoza

Edwin Curley, trans. and ed. The Collected Works of Spinoza Vol. 1. Princeton: Princeton University Press, 1985.

This is the standard English translation.

Leibniz

Roger Ariew and Daniel Garber trans. and ed. G.W. Leibniz: Philosophical Essays. Indianapolis: Hackett, 1989.

This is a great collection of many of Leibniz’ most important works.

Leroy L. Loemker trans. and ed. Philosophical Papers and Letters 2nd ed. Dordrecht: Reidel, 1969.

This is a much broader collection of Leibniz’s work than the Ariew and Garber text.

b. Secondary Texts

Adams, Robert Merrihew. Leibniz: Determinist, Theist, Idealist. New York: Oxford University Press, 1994.

This is one of the most influential books written on Leibniz in recent years. Adams’ book includes detailed discussions of Leibnizon modality and identity, the ontological argument, and the place of bodies in Leibniz’s mature metaphysics, among other topics.

Carriero, John. “On the Relationship Between Mode and Substance in Spinoza’s Metaphysics,” Journal of the History ofPhilosophy, vol. 33, no. 2 (1995), pp. 245-273.In this article Carriero argues that Spinoza’s account of substance is a traditional one according to which substances areultimate subjects.

Cottingham, John. Descartes. New York: Blackwell, 1986.

This is a good introduction to Descartes thought, and raises the question of a trialist interpretation.

Cottingham, John. The Rationalists. Oxford: Oxford University Press, 1988.

This is a clearly written summary and comparison of the philosophies of Descartes, Spinoza, and Leibniz. Chapter 3 onsubstance is recommended.

Della Rocca, Michael. “Spinoza’s Substance Monism,” Spinoza: Metaphysical Themes. Ed. Olli Koistinen and John Biro.Oxford: Oxford University Press, 2002.

In this article Della Rocca considers Spinoza’s official argument that there is only one substance, and defends it from a number ofobjections—including the claim that Spinoza is not entitled to hold that substance can have more than one attribute.

Della Rocca, Michael. Spinoza. Routledge: 2008.

This book is an excellent overview of Spinoza’s life and philosophy; Della Rocca’s discussion of Spinoza’s account of substance incontrast to Descartes’ is especially good.

Huenemann, Charles. “Predicative Interpretations of Spinoza’s Divine Extension,” History of Philosophy Quarterly, vol.14, no. 1 (1997), pp. 53-76.In this article Huenemann offers an account of Spinoza’s extended substance which differs from other influential interpretationsin important ways. In doing so, he takes up the question of the divisibility of substance and Spinoza’s vacuum argument.

Hoffman, Paul. “The Unity of Descartes’s Man,” Philosophical Review, vol. 95, no. 3 (1986), pp. 339-370.In this often cited article, Hoffman makes the case for a trialist reading of Descartes and along the way offers a number ofcriticisms of monist interpretations of substance.

Hoffman, Joshua, and Rosenkrantz, Gary S. Substance: Its Nature and Existence. Routledge, 1997.

In this book Hoffman and Rosenkrantz draw on the ideas of philosophers from the past (including Descartes, Spinoza, andLeibniz) as well as from contemporary philosophical advancements to develop and defend an account of substance based onindependence.

Jolley, Nicholas. Leibniz. Routledge: 2005.

This book is an excellent overview of Leibniz’s life and philosophy. The book is written for the non-specialist and would be agood place for a person with no previous knowledge to start.

Kaufman, Dan. “Descartes on Composites, Incomplete Substances, and Kinds of Unity,” Archiv für Geschichte derPhilosophie, vol. 90, no. 1 (2008), pp. 39-73.

In this excellent article Kaufman argues the Descartes is a dualist and that the trialist interpretation espoused by Hoffman (seeabove) and others is mistaken.

Lin, Martin. “Spinoza’s Arguments for the Existence of God,” Philosophy and Phenomenological Research, vol. 75, no. 2(2007), pp. 269-297.

In this article Lin takes a new look at Spinoza’s arguments for God’s existence, and attempts to defend Spinoza from the chargethat it is incoherent to think that God’s has more than one (much less, all) the attributes.

Loeb, Louis E. From Descartes to Hume: Continental Metaphysics and the Development of Modern Philosophy.Ithaca: Cornell University Press, 1981.

This book is one of the standards of the field, and in chapter 2 Loeb offers a comparison of Descartes, Spinoza, and Leibniz onsubstance.

Markie, Peter. “Descartes’s Concepts of Substance,” Reason, Will and Sensation: Studies in Descartes’s Metaphysics.Ed. John Cottingham. Oxford: Clarenden Press, 1994.

In this influential article, Markie claims to find not two, but three accounts of substance in Descartes’ work.

Robinson, Thaddeus S. “Spinoza on the Vacuum and the Simplicity of Corporeal Substance,” History of PhilosophyQuarterly, vol. 26, no.1 (2009), pp. 63-81.

In this article Robinson offers a novel interpretation of Spinoza’s vacuum argument, and makes the case that Descartes’ accountof extended substance, at least by Spinoza’s lights, is incoherent.

Rodriguez-Pereyra, Gonzalo. “Descartes’s Substance Dualism and His Independence Conception of Substance,” Journalof the History of Philosophy, vol. 46, no. 1(2008), pp. 69-90.

In this article Rodriguez-Pereyra focuses on clarifying the respects in which Descartes’ substances are independent, and arguesthat other prominent features of Descartes’ account of substance follow from independence so understood.

Rutherford, Donald. Leibniz and the Rational Order of Nature. Cambridge: Cambridge University Press, 1995a.Although written for specialists, this influential book is highly readable. Rutherford offers an account of Leibniz’s metaphysicswhich gives Leibniz’s theodicy and especially important role.

Rutherford, Donald. “Metaphysics: The Late Period.” The Cambridge Companion to Leibniz. Ed. Nicholas Jolley. Cambridge: Cambridge University Press, 1995b.

This article is an excellent summary and discussion of Leibniz’s metaphysics from 1695’s New System of Nature to 1714’sMonadology, and focuses on Leibniz’s account of matter during this period.

Skirry, Justin. Descartes and the Metaphysics of Human Nature. New York: Continuum, 2005.

This book traces Descartes’ scholastic influences and develops a pluralist and trialist interpretation of Descartes’ account ofsubstance.

Sleigh, R.C. Leibniz and Arnauld: A Commentary on Their Correspondence. New Haven: Yale University Press, 1990.

This is an extremely influential book which offers a reading of one of the most important of Leibniz’s philosophical exchanges.

Slowik, Edward. “Descartes and Individual Corporeal Substance,” British Journal for the History of Philosophy, vol. 9no. 1 (2001) pp. 1-15.

Slowik picks up where Hoffman leaves off, developing several arguments against the monist interpretation of Descartes.

Woolhouse, R.S. “Spinoza and Descartes and the Existence of Extended Substance,” Central Themes in Early ModernPhilosophy. Ed. J.A. Cover and Mark Kulstad. Indianapolis: Hackett, 1990.In this article Woolhouse offers a novel reading of Spinoza’s extended substance, claiming that it refers to an essence asopposed to an actually existing infinite extension.

Woolhouse, R.S. The Concept of Substance in Seventeenth Century Metaphysics. New York: Routledge, 1993.

This is a good general work on substance during the 17th century. In addition, Woolhouse offers novel readings of Descartesand Spinoza (see above) on extended substance. This work offers an especially good look at the relations between mechanics,causation, and substance during the period.

Zaldivar, Eugenio E. “Descartes’s Theory of Substance: Why He Was Not a Trialist,” British Journal for the History ofPhilosophy, vol. 19, no. 3 (2011), pp. 395-418.

The title says it all. Zaldivar argues against Cottingham, Skirry, and others.

Author Information

Tad RobinsonEmail: trobinson@muhlenberg.edu

Mullenburg CollegeU. S. A.

Last updated: January 9, 2013 | Originally published: January 8, 2013

Article printed from Internet Encyclopedia of Philosophy: http://www.iep.utm.edu/substanc/

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