James Messina

Kantian Space, Supersubstantivalism,and the Spirit of Spinoza

Abstract: In the first edition of Concerning the Doctrine of Spinoza in Letters toMendelssohn, Jacobi claims that Kant’s account of space is “wholly in the spiritof Spinoza”. In the first part of the paper, I argue that Jacobi is correct: Spinozaand Kant have surprisingly similar views regarding the unity of space and themetaphysics of spatial properties and laws. Perhaps even more surprisingly,they both are committed to a form of parallelism. In the second part of thepaper, I draw on the results of the first part to explain Kant’s oft-repeatedclaim that if space were transcendentally real, Spinozism would follow, alongwith Kant’s reasons for thinking transcendental idealism avoids this nefariousresult. In the final part of the paper, I sketch a Spinozistic interpretation ofKant’s account of the relation between the empirical world of bodies and(what one might call) the transcendental world consisting of the transcendentalsubject’s representations of the empirical world and its parts.

1 Introduction

Amidst the Pantheismusstreit sparked by Jacobi’s Concerning the Doctrine of Spi-noza in Letters to Mendelssohn, Christian Schütz sent Kant a letter asking himwhether Jacobi was correct in claiming that Kant’s ideas about space are “whollyin the spirit of Spinoza”.¹ The claim Schütz is referencing occurs in a footnote inwhich Jacobi calls attention to similarities in Kant and Spinoza’s views about thestructure of space and time.² Along with the companion remark about time,³

Jacobi cites the following remark about space from Kant’s Transcendental Aes-thetic:

For, first, one can only represent a single space, and if one speaks of many spaces, one un-derstands by that only parts of one and the same unique space. And these parts cannot as itwere precede the single all-encompassing space as its components (from which its compo-

AA 10:430. For quotations of Kant, I rely on translations in the Cambridge edition of his works,where these are available. Page references to the first Critique are to A and B editions. For otherworks, I give Akademie-Ausgabe page numbers. Jacobi (1994, 218) I will here be focusing on space rather than time.

sition would be possible) but are rather only thought in it. It is essentially single; the mani-fold in it, thus also the general concept of spaces in general, rests merely on limitations.⁴

For Kant, space is an essentially unitary, infinite whole – all other spaces areparts contained within it. Far from composing the whole of space, the parts ofspace can only emerge out of the whole, by limiting it. In this respect, thewhole of space is like a sheet of cookie-dough, and its parts individual cookies.As emerges immediately after this passage in the next argument of theAesthetic,⁵ and becomes yet clearer later in the Critique of Pure Reason (CPR),Kant has the same account of the representation of the whole of space: it, too,is an essentially unitary, infinite whole, one that contains representations ofall other spaces within it as its parts.

Whatever Jacobi’s actual intentions were in pointing to this spiritual affinity,at least one representative reader, namely Schütz, apparently took Jacobi to beaccusing Kant of Spinozism. ⁶ Unfortunately, we do not have Kant’s reply toSchütz’s letter. But it is likely that Kant pointed to a key difference between him-self and Spinoza: namely, space for Kant is transcendentally ideal, which means,among other things, that everything noumenal (including God) is exempt fromspatiotemporality. By contrast, Spinoza maintains that God is spatially extended.But once one moves beyond this admittedly, quite significant disagreement,there are arguably equally significant agreements. Kant himself concedes the log-ical power of Spinoza’s Raumlehre in various remarks to the effect that, if oneaccepts the transcendental reality of space, Spinozism follows.⁷ By Spinozism,Kant seems to mean not just the claim that all things are spatial, but alsowhat I will call supersubstantivalist necessitarianism (SN): the claim that things

CPR A 25/B 39. See also CPR A 438/B 466 and AA 4:286 (Prolegomena). CPR A 24/B 39–40. In the 1789 edition of his work, Jacobi removed the “wholly in the spirit of Spinoza” remarkand inserted in its place an explicit denial that Kant is a Spinozist. It is of course possible thatJacobi meant this and was genuinely disappointed that readers had misunderstood his 1785remark about Kant, but it is also possible that he had meant it in the way it was understood butlater found it prudent not to jeopardize his tenuous relationship with Kant. Alternatively, he mayhave originally meant the remark but then revised it in disappointment after reading Kant’s(uncharitable and unsophisticated) remarks about Spinoza in What Does it Mean to OrientOneself in Thinking. In any case, for the sake of this paper, I can remain agnostic about whetherand to what extent Jacobi thought of Kant as a Spinozist. This footnote was prompted by ahelpful comment from an anonymous referee for this journal. See, e.g., AA 5:101–102 (Critique of Practical Reason), AA 28:803 (Metaphysik K2), AA 28:666(Metaphysik Dohna), and AA 28:567 (Metaphysik L2). These passages are helpfully gatheredtogether in Hogan (2009).

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in space are really just properties of space and that space is endowed with lawsthat fully determine what properties are instantiated by it when. ⁸ Unfortunately,Kant does not clearly explain what it is about Spinoza’s theory of space thatmakes it the only logically permissible transcendental realist account, nordoes he explain how transcendental idealism avoids SN. ⁹ The last question isparticularly pressing, if indeed there is a measure of truth in Jacobi’s claimthat Kant’s theory of space is “wholly in the spirit of Spinoza”. Moreover, the an-swer is not obvious, when one considers that Kant’s restriction of space to ap-pearances is, on its own, consistent with (what Kant would regard as) an unac-ceptable supersubstantivalist necessitarianism holding at the level ofappearances.

I have three goals in this paper. First, I will attempt to determine the depth ofthe spiritual affinity between Kant and Spinoza’s views of space. Here I willargue that the following version of the spiritual affinity thesis is correct (whetheror not this is the one intended by Jacobi): Spinoza and Kant have surprisinglysimilar views regarding the structure of space – in particular, regarding theunity of space, the metaphysics of spatial properties, and the laws governingsuch properties. Perhaps even more surprisingly, with regard to the structureof the representation of space, they both are committed to a form of parallelismholding between spatial representations and their corresponding objects.¹⁰ Sec-ond, I will examine Kant’s claim that if space were transcendentally real, SNwould follow, along with his reasons for thinking that transcendental idealismavoids SN. As I argue, Kant thinks that SN follows from the conjunction of certain

For evidence that Kant’s understanding of Spinozism included supersubstantivalist necessi-tarianism, see AA 23:31–32 (Reflections) and AA 5:393 (Critique of Judgment). As I will argue in§ 4, Kant alludes to and attacks supersubstantivalist necessitarianism as early as the InauguralDissertation. It may be that Kant also meant Spinozism to include more than supersubstantivalistnecessitarianism. See the next footnote in this regard. Kant’s attitude towards Spinozism – especially his view that transcendental realism requiresSpinozism while transcendental idealism avoids it – is a large, multifaceted topic. My work hereis meant to supplement several recent contributions (rather than compete with them). Thecontributions have focused, for example, on Kant’s only possible argument (see Chignell 2009),the Fourth Antinomy and Transcendental Ideal (see Boehm 2012), and Kant’s views on freedomand God’s grounding of appearances (see Brewer and Watkins 2012). Here, I try to show howcertain assumptions about space that Kant and Spinoza hold in common lead to supersub-stantivalist necessitarianism when combined with transcendental realism but not when com-bined with transcendental idealism. This is fully compatible with Kant thinking that there arealso other philosophical considerations that push the transcendental realist towards Spinozismbut allow the transcendental idealist to avoid it. I should say up front that in arguing for the spiritual affinity thesis, I am not trying toestablish any direct influence of Kant by Spinoza.

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views about the structure of space that he holds in common with Spinoza andthe transcendental realist assumption that space is a fully determinate object.What allows transcendental idealism to escape Spinozism, understood as SN,is not (as one might expect) that transcendental idealism restricts space to ap-pearances, but rather that it regards space as something merely formal and in-determinate with respect to forces and dynamical laws. In the final part of thepaper, I draw on the results of the first part to shed light on Kant’s account ofthe relation between the empirical, physical world and (what one might call)the transcendental world consisting of the transcendental subject’s representa-tions of the empirical, physical world. My suggestion is that, just as Spinoza re-gards corresponding modes of extension and thinking not as distinct entities butrather as one-and-the-same-thing expressed in two different ways, so might Kanthold the same of the components and conditions of the physical world and thecorresponding components and conditions of the transcendental world.

2 The Structure of Space

The spiritual affinity thesis can be broken down into two parts, one concerningthe structure of space, the other concerning the structure of the representation ofspace. In this section I evaluate the first part of the spiritual affinity thesis. Forthe purposes of this discussion, an account of the structure of space includes ac-counts of the following: the unity of space, the metaphysics of spatial properties,and the laws governing such properties. As we will see, for both Kant and Spi-noza these issues are closely connected.

Prominent in Kant’s own account of the unity of space is a claim about thepriority of the whole of space to its parts. We find such a claim not just in thepassage from the Transcendental Aesthetic quoted above but also, amongother places, in the Second Antinomy: “Properly speaking, one should callspace not a compositum but a totum, because its parts are possible only in thewhole, and not the whole through the parts” (CPR A 438/B 466). How do Spino-za’s views compare with Kant’s?

The first passage to consider in this regard occurs in the Ethics immediatelyfollowing Spinoza’s proof that God is the only substance. In response to variousarguments aimed at showing that God could not be extended since extended be-ings are divisible, Spinoza writes:

[…] [T]he student who looks carefully into these arguments will find that I have already re-plied to them, since they are all founded on the same supposition that material substanceis composed of parts, and this I have already shown to be absurd (Pr. 12 and Cor. Pr. 13) […]

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For corporeal substance, which can be conceived as infinite, one, and indivisible (Prs. 8, 5,and 12) they conceive as made up of finite parts, multiplex, and divisible, so as to deducethat it is finite.¹¹

By corporeal substance, Spinoza is referring to infinite, three-dimensional space,each region of which he, following Descartes, takes to be full of body.

It might initially be thought that there is an important difference betweenKant and Spinoza insofar as Spinoza appears to be denying the divisibility ofspace while Kant merely maintains the whole-part priority of space, without de-nying spatial parts. However, Spinoza’s claim is not that there are no spatialparts. Instead, he is making the following tripartite claim: (i) the parts ofspace are not substances but rather modes (or properties) of space; (ii) theparts of space do not compose it but rather arise through limitation; and (iii)the parts cannot be divided or taken away from space.¹² Claim (ii) evinces thesame cookie-dough model and part-whole priority we saw in Kant. Claim (iii)is a statement that Kant would accept, given his own commitment to the “essen-tial unity” of space. As for (i), as we’ll see, Spinoza and Kant agree that the partsof space, understood as determinate regions of space, are properties of the wholeof space.

Spinoza’s commitment to the existence of parts of space is confirmed by aletter to Oldenburg in which he describes finite spaces cum bodies as parts ofthe whole of (extended) Nature. Spinoza’s talk here of a “harmony” and “adap-tation” among the “natures or laws” of these parts brings up a further similaritywith Kant.¹³ For Spinoza, the essential unity of space means not just that all spa-tial parts necessarily belong to a single space but that the properties of each partare necessarily connected to the properties of other parts in accordance with amaximally intelligible and fruitful system of laws. These laws range from verygeneral laws grounded in extension as a whole to specific laws grounded inthe specific “natures” of each part of space. An example of the latter wouldbe theorem 35 of Book 3 of Euclid’s Elements, which Spinoza alludes to in Ethics2P8: “The nature of a circle is such that the rectangles formed from the segmentsof its intersecting chords are equal”.¹⁴ This theorem represents a law correlatingthe properties of circular regions of space with the properties of certain rectan-gular regions inscribed within them. Examples of the very general laws would

Spinoza (2002, 226). In other words, Spinoza’s claim is not that corporeal substance has no parts but that it hasno parts in what Bennett (1984, 88) calls a “damaging sense” of ‘part’. Spinoza (2002, 848). Spinoza (2002, 248).

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presumably include Euclid’s Postulates, as well as the axioms of motion laid outin Ethics 2.

In pre-Critical and Critical works, Kant similarly speaks of “how immeasur-ably great is the number of harmonious relations which inhere in the propertiesof space in general”,¹⁵ using (among other things) theorem 35 to illustrate thisphenomenon.¹⁶ Like Spinoza, Kant holds that the unity of space involves morethan singularity: it also means that the properties of parts of space are connectedto each other in accordance with a maximally intelligible and fruitful system oflaws.¹⁷ Some of these laws are geometrical (for example, theorem 35); other lawsare more abstract and metaphysical, describing for instance the function ofspace (e.g. “space makes possible only reciprocal relationships”¹⁸). As Kantmakes clear in the Only Possible Argument and elsewhere, these laws of spaceare closely related to dynamical laws governing the interaction of matter. For ex-ample, the fact that attraction between bodies is subject to an inverse-square lawfollows from the geometrical properties of concentric spherical surfaces (assum-ing, that is, that there is an attractive force and that it radiates outward from cen-tral points).¹⁹ To give another example (involving a “metaphysical” law of space),the fact that action is equal to reaction apparently follows from the truth that“spatial relationships are reciprocal”.²⁰ Given the dynamical implications ofthe laws of space, the harmony of space is evidence for a dynamical harmonyamong all material things. These harmonies, Kant stresses, are necessary ones,attaching to spatial things in their very essence.

Because of Spinoza’s identification of body and extension, he would have nodifficulty accepting Kant’s view that there is an intimate relationship between(what I am calling) laws of space and dynamical laws. Indeed, extension for Spi-noza is a manifestation of God’s power, meaning that it and its parts are essen-

AA 2:95. AA 2:94. Like Spinoza, Kant seems to have been particularly fond of this theorem. He alsodiscusses it at AA 4:320 (Prolegomena) and AA 5:362–363 (Critique of Judgment). That Kant continues to hold this account of space in the Critical period is evident from § 62 ofthe Critique of Judgment, where he describes the harmony of space in terms nearly identical tothose of the Only Possible Argument. See also AA 4:320–322 (Prolegomena), which is discussedfurther below. See, for example, AA 11:246 (Letter to Christoph Friedrich Hellwag) and AA 2:414 (InauguralDissertation). See, for instance, AA 1:484 (Physical Monadology) and AA 4:321 (Prolegomena). For a helpfuldiscussion of Kant’s derivation of the inverse-square law from such geometrical considerations,see Friedman (1992, 166) and Friedman (2013, 224–225). Kant gives precisely such a derivation in a letter; see AA 11:246–247.

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tially dynamical.²¹ This helps to explain why, as mentioned above, the laws gov-erning the whole of space include for Spinoza the laws of motion.²² Spinoza alsoagrees with Kant that harmony is not a contingent feature of the parts of spacebut rather rooted in their respective natures. The “natures” Spinoza discusses inthe letter are what he elsewhere calls “formal essences”. These are sets of pos-sible spatial (and dynamical) properties, specifying, for example, the figure,magnitude, and state of motion of some possible spatial individual.²³ The instan-tiation of such a set of properties is an actually existing (i.e. durational) spatialindividual. Formal essences are eternally “contained” in the attribute of exten-sion, in contrast to the actually existing individuals that result from their instan-tiation, which only enjoy a temporary existence as parts contained within thewhole of space.²⁴ Formal essences and the specific laws linking them togetherfollow from the most general laws of space as a whole, as the set of all possibleways in which this whole can be modified. The parts of space, then, are instan-tiations of formal essences that are eternally contained in the whole of space aspossible modifications of it.

Kant similarly speaks of the whole of space as containing within it all pos-sible spatial properties, namely, figure, magnitude, and relation (i.e. position).In the First Antinomy, he speaks of appearances determining space “amongall its possible predicates (magnitude and relation)”.²⁵ And in the Transcenden-tal Ideal, in a passage that has struck many as Spinozistic (albeit for otherreasons),²⁶ Kant draws an explicit comparison between space and the ens realis-simum:

All manifoldness of things is only so many different ways of limiting the concept of thehighest reality, which is their common substratum, just as all figures are possible only asdifferent ways of limiting infinite space. (CPR A 578/B 606)

It is reasonable to think that this claim extends beyond figure, to the specificmagnitudes and relative positions possessed by parts of space. For such partsto exist just is for a certain set of mutually compossible spatial properties tobe instantiated. Possible spatial properties are, as it were, stored in the whole

This aspect of Spinoza’s view is rightly emphasized in Viljanen (2013). As we will see below, from Kant’s standpoint, Spinoza goes too far in taking dynamical lawsto be inherent to space. I have found Garrett (2010) especially helpful for understanding Spinoza’s account of formalessences. See Ethics 2P8 (Spinoza 2002, 248). CPR A 431/B 459. See, e.g., Melamed (2012, 183).

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of space. In this respect, the whole of space is a subset of what Kant calls in theTranscendental Ideal “the whole of possibility”.²⁷ As with Spinoza, sets of pos-sible properties are eternally contained in the whole of space, as the variousways in which that indeterminate infinite whole can be limited. The whole ofspace serves as a substratum for these properties and thus for the individuals– including the parts of space – that result from their instantiation.

In short, the similarities in Kant and Spinoza’s views of the structure ofspace are substantial. Kant and Spinoza agree that the whole of space precedesand contains not only all the parts of space but also, more fundamentally, allpossible sets of spatial properties; that these possible properties are possibleways of limiting the whole of space; that space is the substratum for these prop-erties and in turn for the parts that result from their instantiation; that theseproperties are linked to each other in intricate ways by laws of space; and thatthe laws of space are closed tied to physical laws governing the force and motionof bodies.

3 The Structure of the Representation of Space

In § 4 I will use Kant and Spinoza’s shared commitments about the structure ofspace to shed light on Kant’s claim that, assuming transcendental realism, Spi-nozism follows. Before I do this, though, I will evaluate in this section the secondpart of the spiritual affinity thesis, which says that, in addition to agreeing aboutthe structure of space, Kant and Spinoza have similar views on the structure ofthe representation of space.

Understanding Spinoza’s account of the structure of the representation ofspace requires understanding his (in)famous doctrine of parallelism, expressedat Ethics 2P7: “The order and connection of ideas is the same as the order andconnection of things” (Spinoza 2012, 247). In other words, there is a parallelismbetween the modes that fall under the attribute of thought (ideas) and the modesthat fall under the attribute of extension (including bodies). For every body thereis a corresponding idea of that body; that idea relates to other ideas in the sameway that the corresponding body relates to other bodies. For example, corre-sponding to my arm is the idea of my arm and corresponding to my body isthe idea of my body. Just as my arm is part of my body, so is the idea of myarm a part of the idea of my body. Similarly, there is the whole of space. Corre-sponding to this is an idea of the whole of space (that is, the whole of extended

CPR A 572/B 600.

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Nature), which contains within it as parts ideas corresponding to all the partic-ular regions of space cum bodies. The idea of the whole of space is a particularinstance of the “infinite idea of God”, where the “of” is both genitive and dative:it is the idea that God forms of its own essence and of what follows from it (Spi-noza 2002, 245). Spinoza identifies this idea with the divine intellect (“infiniteintellect”) and regards it as an infinite mode of thinking. The idea of thewhole of space is God’s infinite idea of itself qua spatial (as opposed to quathinking or qua some other attribute).²⁸

For present purposes, two features of Spinoza’s parallelistic account are wor-thy of note. First, for Spinoza, the isomorphic relationship between a given finitemode of extension and the corresponding idea that is ‘of ’ that mode is explainedby their underlying identity and the underlying identity of the respective (infin-ite) modes containing them. My body and the idea corresponding to it that iscontained in God’s idea of space are actually the same thing expressed in twoways (in two languages, as it were), as are the whole of infinite space andGod’s idea of it. Because of this underlying identity, my body’s place in theorder of bodies is parallel to the idea of my body’s place in the order of ideas.

Second, Spinoza holds that the necessary unity of the idea of the whole ofspace is not a brute fact but rather requires some explanation. Necessary“unity” here means, as it does in the case of space, both singularity and the dis-tinctive kind of harmony among parts described above, though here the parts arethemselves representations and the laws connecting them are presumably repre-sentational versions of the “laws of space”. Spinoza’s rejection of brute facts is aconsequence of his commitment to the thoroughgoing validity of the principle ofsufficient reason: ²⁹ there is a ground and accompanying explanation for everystate of affairs, even of modal states of affairs like the necessary facts thatGod exists and that space is a unity. Given Spinoza’s view that nothing underone attribute can explain anything under another attribute, the explanation ofthe unity of the idea of the whole of space must be something under the attributeof thinking. Though he is not explicit on this point, his implicit explanation Itake it is that the necessary unity of the idea of the whole of space is explainedby the necessary unity of the divine idea. (Spinoza gives a proof of the unity ofthe divine idea at Ethics 2P4.) Given that the idea of the whole of space is a par-ticular instance of God’s idea of his entire essence – it is God’s idea of his entire

Admittedly, the distinction between the idea of God and the idea of the whole of space is notone that, to my knowledge, Spinoza explicitly draws, though it seems to me implicit in hisaccount. This aspect of Spinoza’s position is rightly emphasized in Michael Della Rocca’s work. See,for example, Della Rocca (2008, 1– 10).

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essence under the attribute of extension – and given that the latter idea is a nec-essary unity, it follows that the representation of the whole of space is a neces-sary unity.

When we compare Spinoza and Kant’s views, some surprising similaritiesemerge. First of all, like Spinoza, Kant is committed to a form of parallelism.Such a view is suggested early on in the Critique, in the fourth argument ofthe metaphysical exposition of space, where Kant describes the intuition of(the whole of) space as containing an infinite number of intuitions “within itself”(CPR A 25/B 40). But the parallelism is made more explicit later in the Critique, ina footnote to the B-Edition of the Transcendental Deduction:

Space and time and all their parts are intuitions, thus individual representations along withthe manifold that they contain in themselves (see the Transcendental Aesthetic), thus theyare not mere concepts by means of which the same consciousness is contained in manyrepresentations, but rather are many representations that are contained in one and inthe consciousness of it; they are thus found to be composite, and consequently, theunity of consciousness, as synthetic and yet as original, is to be found in them. This singu-larity of theirs is important in its application (see §25). (CPR B 136*)

There is, for Kant, a representation of the whole of space (which Kant calls, al-ternately, a formal intuition and a pure intuition) that contains within it, asparts, all representations of all the parts of space (particular places withinspace). The mereological structure of the intuition of the whole of space mirrorsthe mereological structure of its representational object (the whole of space). Aswas the case with Spinoza, a given representation of a part of space is connectedto representations of other parts of space and the whole of space in the way thatthe corresponding parts of space are connected to each other and the whole ofspace.

To give one example of this: if a given set of parts of space are combined intoa single quantity, like a line, the corresponding representations of these parts arecombined by the transcendental self (using the category of quantity) into a sin-gle representation of that line. To give another example: if a set of physical ob-jects occupying distinct parts of space (for example, the sun and a stone) areconnected by causation to form one state of affairs (the sun warms the sun),then the corresponding (empirical) intuitions of these physical objects are com-bined by the transcendental self (using the category of causation) to form a sin-gle representation (an objective experience) of that state of affairs (the sunwarming the stone). This particular objective experience, in turn, relates toother objective experiences and the whole of experience in the way that the

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physical states of affairs corresponding to these experiences relate to eachother.³⁰ To put this in Descartes and Spinoza’s language: the structure of the rep-resentation of the whole of space and the representations of the things in it intheir formal reality is parallel to their structure in their objective reality.

What explains this parallelism of representation and its objective reality? Ar-guably, for Kant, as for Spinoza, the explanation is that a given space (whether apart of space or the whole) and the corresponding representation of it are reallyjust the same thing expressed in two different ways. Throughout the Critique,Kant slides back and forth between talk of space and talk of the pure intuitionof space. This slide is sanctioned by Kant’s transcendental idealist view thatspace is an intuition, which he espouses, among other places, in the last quotedpassage (“space and time and all their parts are intuitions”).³¹ One way of look-ing at such claims is to see a one-sided reduction of space to a particular repre-sentation with spatial content. This is the phenomenalist reading. But accordingto the (Spinozistic) way I am proposing to interpret such claims, space and itsrepresentation are really two equally real aspects of the same underlying reality.Depending on what we are trying to explain, we might concentrate on one aspectover the other, but we can never reduce one aspect to the other. Such a view, as Iwill explain more in the Conclusion, is more in keeping with Kant’s transcenden-tal idealism/empirical realism dichotomy. It also, as I have suggested, providesan explanation for Kant’s otherwise puzzling “parallelism” of spatial representa-tions and their objects.

There is also agreement with respect to the second feature of Spinoza’s ac-count of the structure of the representation of space: the necessary unity ofthe representation of the whole of space requires an explanation. In the OnlyPossible Argument, Kant writes:³²

If, in the case of such arrangements in nature, we are justified in searching for the founda-tion of the extensive harmony of the manifold, are we less justified in searching for a sim-ilar foundation for the regularity and unity which we perceive in the infinitely various de-terminations of space? Is this harmony any the less amazing for being necessary? (AA 2:95)

Kant’s remark at CPR A 110 suggests just such a similarity between the structure of objectiveexperience and the structure of the representation of space. See also CPR A 374 and A 429/B 457*. In this remark, Kant speaks of space rather than the representation of space, but if I amcorrect that he is committed to parallelism and accepts an underlying identity of the re-presentation of the whole of space and the whole of space, then what he says about the unity ofspace carries over immediately to the unity of the representation of space.

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In the Inaugural Dissertation, Kant claims that the unity of space and time “bearwitness to some common principle constituting a universal connection”(AA 2:391). A reflection from around the same time makes clear what this “com-mon principle” is:

The first ground of combination is also the formal ground of the possibility of community.Sensibly expressed it is space. However, space is presumably only sensible intuition, whichthe immediate consciousness (intellectual intuition) underlies, but cannot be found thereinthrough analysis. (AA 17:456)

By intellectual intuition, Kant means of course God’s creative intuition. For thepre-Critical Kant, the explanation of the necessary unity of the intuition ofspace is, as for Spinoza, the unity of God’s representation of things: the neces-sary unity of the representation of space is an “expression” of the necessaryunity of God’s creative representation. It is this grounding relation betweenthe unity of the intuition of space and the unity of the divine idea that leadsKant at the very end of the Inaugural Dissertation to connect his account to Mal-ebranche’s doctrine of “vision in God”. Since this Malebranchian view placesone’s intuitions of space and of things in space into the divine intellect (becausethese intuitions are just particular expressions of God’s representation), Kant as-sociates it in the Opus Postumum with Spinoza.³³ This suggests that Kant himselfmight have seen something Spinozistic about his early account but, for obviousreasons, preferred to associate it with Malebranche in print.

To be sure, Kant’s views on the explanation of the unity of the representationof space undergo a shift between the Inaugural Dissertation and the Critique,where critical strictures outlaw any claim to theoretical knowledge to the effectthat the unity of the divine representation is the ground of the unity of the rep-resentation of space. At the same time, Kant’s belief that the unity of the repre-sentation of space requires an explanation does not go away. It is just that Kantcomes to think that the only theoretically justified explanation of this unity is anexplanation couched in terms of a distinctive sort of unity characteristic of a dis-cursive (that is, human or human-like) intellect as opposed to an intuitive (thatis, divine) intellect. The former is the synthetic unity of apperception discussedat CPR B 136*(which I quoted at the outset of this section). At the same time,texts from the time-period between the Inaugural Dissertation and the Critiquesuggest that Kant continues to see God’s intuition as simultaneously playing agrounding role with respect to the unity of the representation of the whole of

See, e.g., AA 21:48 and AA 21:50.

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space.³⁴ Given Critical strictures, Kant must regard his belief to this effect as hav-ing merely practical status.³⁵

Whatever the details of Kant’s position (particularly, how the synthetic unityof apperception and God are supposed to ground the unity of the representationof space), it is clear that there is, both in the pre-Critical and Critical period, sig-nificant overlap between his representational monism and Spinoza’s. Both es-pouse a parallelism of representation and its objective reality; both explainthis parallelism through the underlying identity of the items in parallel; andboth regard the necessary unity of the representation of space as requiring anexplanation in terms of a mind or minds (whether divine, discursive, or a com-bination of both).

4 Supersubstantivalist Necessitarianism

One reason the first part of the spiritual affinity thesis (which deals with Kantand Spinoza’s views about the structure of space rather than the structure ofthe representation of space) is of interest is that it helps to explain Kant’s oft-re-peated claim that transcendental idealism aside, Spinozism is the only game intown. The particular position Kant has in mind involves, first, a kind of super-substantivalism, according to which the whole of space is a substance and allthings in space are merely properties of it.³⁶ Second, it involves necessitarianism,which when combined with substantivalism, leads to what I will call supersub-stantivalist necessitarianism (SN): things and events in the physical world arereally sets of properties instantiated successively by space and necessitatedfrom the top-down by its basic laws. Kant alludes to SN in the Inaugural Disser-tation:

For, since whatever things exist are, in their [i.e. the Newtonians’] opinion, necessarilysomewhere, it appears superfluous to them to enquire why these same things are present

Indeed, in the following fascinating reflection, likely written between 1775 and 1777, we seehints of a two-level explanation: “The understanding itself (a being that has understanding) issimple. It is substance. It is transcendentally free. It is affected with sensibility (space), [it is] in acommunity with others. All objects of it constitute one (composite), which is called world (unityof space)…. Everything rests on an original understanding that is the self-sufficient ground of theworld. The (necessary) unity of time and space is transformed into the necessary unity of anoriginal being, the immeasurability of the former into the self-sufficiency of the latter” (AA17:707). I explore this issue in other work. Bennett (1984, 89ff.) ascribes a similar supersubstantivalism to Spinoza.

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to one another in a fixed manner. For this, it seems to them, would be determined in itselfby the entirety of space, which includes all things.³⁷

SN doesn’t come cheap. It assumes the part-whole priority and essential unity ofspace. It assumes that parts of space are properties of space as a whole and thatspace has laws connecting spatial properties with each other. Finally, it assumesthat these laws have dynamical implications. As we have seen, Kant and Spinozaactually share these strong assumptions. My suggestion is that, in Kant’s eyes,the logical power of Spinozism is due to its clear-eyed acceptance of them andof their logical implications when combined with transcendental realism. Kantregards Spinozism as the best of the transcendental realist accounts becausehe thinks that these assumptions, together with the assumed transcendental re-ality of space, entail SN. From Kant’s standpoint, to be, say, a Newtonian andresist SN is not logically viable. This explains why in the Inaugural DissertationKant describes the Newtonian position in SN-terms.

But what is it about transcendental realism that makes it react so catastroph-ically with these shared assumptions? Conversely, what is it about transcenden-tal idealism that defuses the reaction? It cannot be solely the fact that transcen-dental idealism restricts space to appearances while transcendental realismascribes it to all things whatsoever.³⁸ After all, it is possible to imagine a positionaccording to which space is merely a feature of appearances and SN holds at thelevel of appearances (but not at the level of noumena). Kant would clearly not behappy with such a position.³⁹

Two remarks from the Critical Period shed light on the key feature of tran-scendental idealism that blocks the slide from the shared assumptions to SN:

Space is merely the form of outer intuition, but not a real object that can be externallyintuited, and it is not a correlate of appearances, but rather the form of appearances.Thus space taken absolutely (simply by itself) alone cannot occur as something determin-ing the existence of things, because it is not an object at all, but only the form of possibleobjects. Thus things, as appearances, do determine space, i.e., among all its possible pred-icates (magnitude and relation) they make it the case that this or that one belongs to real-

AA 2:406–407. In Hogan (2009), this aspect of transcendental idealism is, I think mistakenly, emphasized asblocking Spinozism. See AA 5:393 (Critique of Judgment) in this regard. Kant’s account of free will requires thatthere be some sense in which the order and content of appearances could have been different(namely, if determinations at the noumenal level had been different).

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ity; but space, as something subsisting in itself, cannot conversely determine the reality ofthings in regard to magnitude and shape, because it is nothing real in itself.⁴⁰

Space is something so uniform, and so indeterminate with respect to all specific properties,that no one will look for a stock of natural laws within it.⁴¹

The transcendental idealist regards space not as a fully determinate, real object,but rather as an indeterminate, inert form. Lacking from space in particular arethe forces and natural (that is, dynamical) laws that determine, from the set of allpossible spatial properties (position, figure, and magnitude) contained in space,which sets are instantiated when. Such forces and laws are supplied by the mat-ter (the “real”) that fills space. It is the role of the forces and dynamical laws as-sociated with the matter in space – and not the role of space itself – to determinewhat specific spatial properties are instantiated at what times.⁴²

By contrast, the role of space is to “make possible” the exercise of force bythe matter in space,⁴³ and to impose through its laws certain constraints on thelaws in accordance with which force is exercised.⁴⁴ One such constraint is that

CPR A 431/B 459. AA 4:321. Hogan (2009, 372–379) maintains that for Kant space and time “impose” a deterministicorder on the things that occupy them. If Hogan merely means that, for Kant, everything in spaceand time is deterministic, and that this can be known a priori by considering our a priorirepresentations of these things, then this is consistent with my interpretation. By contrast, if hemeans that space and time are literally the (metaphysical) grounds of the deterministic order,then his position is incompatible with mine and I think in conflict with the most natural readingof the passages cited above. On my interpretation, space would literally impose a deterministicorder (a la supersubstantivalist necessitarianism) only if it were transcendentally real. I emphasize this aspect of Kant’s position in other work. In interpreting Kant’s claim at Prolegomena § 38 that space has no natural laws to mean thatit has no inherent dynamical laws while it does have other inherent – geometrical and meta-physical – laws, I am in agreement with Friedman (1992). A proper understanding of Pro-legomena § 38 requires distinguishing two distinct issues that Kant touches on there (withoutadequately separating them): (1) whether the intuition of space on its own (without the und-erstanding synthesizing it in accordance with its concepts of objects) can yield knowledge oflaws (whether geometrical or dynamical), and (2) whether space (when synthesized by theunderstanding in accordance with its [dynamical] categories) has laws that ‘determine’ theproperties of its material occupants, or whether instead these laws have their seat in the materialoccupants of space (when these occupants are synthesized by the understanding in accordancewith its dynamical categories). (2) is a metaphysical question that is also formulated in theInaugural Dissertation and in the passage from the Antinomies quoted above. Kant answers both(1) and (2) with ‘no’ in Prolegomena § 38. This is consistent with his holding that space, whensynthesized by the understanding in accordance with mathematical categories, is the seat ofgeometrical and metaphysical laws.

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the exercise of force be reciprocal and equal. Another such constraint is that at-tractive force be exercised in accordance with an inverse-square law. Thoughspace is thus linked with dynamical laws, Kant is emphatic that space is not it-self the thing which necessitates the interaction of the matter that is in it, nordoes it determine what sorts of forces and thus what sorts of dynamical lawsare at play. Instead, it is the matter itself that is the source and the locus ofthe forces and corresponding laws.⁴⁵

The above also serves to explain why Kant, in contrast, to Spinoza, does notregard space as a substance, despite the fact that Kantian space has some of thecharacteristics traditionally associated with substance: it is a substratum of allpossible spatial properties (and thus of the parts of space), and it exists inde-pendent of the things occupying it. For Kant, space has no causal powers nordoes it have any laws associated with causal powers. Thus, it lacks a key featureof substantiality: (lawful) activity.⁴⁶

One might wonder why the transcendental realist couldn’t avail herself of amerely formal space of Kant’s sort.Why does she have to accept the substantial-ity of space? One answer would be that it is definitional of transcendental real-ism that space is not a mere form but a complete (that is, fully determinate) ob-ject or property of such objects. A less vacuous answer would be that thetranscendental realist is committed to the principle of thoroughgoing determina-tion for every existing thing: “of every pair of possible predicates, one of themmust always apply to it”.⁴⁷ The transcendental idealist, by contrast, can allowof certain exceptions to this principle.⁴⁸ One such exception occurs in the caseof the whole of space, which is indeterminate with respect to forces and dynam-ical laws, and thus with respect to what sets of possible properties are to be in-stantiated at what times.

Assuming that space is transcendentally real, by contrast, it could not be in-determinate. Moreover, given the transcendental realist’s acceptance of the spa-tial monistic assumptions shared by Kant and Spinoza, she can’t regard thewhole of space as a property of complete objects. Instead, she must take it tobe an entity containing all possible spatial properties and endowed with (dy-namically) determinate laws that in turn determine which sets of propertiesget instantiated in what temporal order. This would mean that the whole of

Recall the example of the inverse square law. Geometrical laws of space necessitate not thatthere be any attractive force in space but only that, if there is such attractive force and it operatesin a specific fashion (radiating out from a central point), then it must obey an inverse square law. CPR A 204/B 249. CPR A 573/B 601. I am indebted to Watkins (2005, 313–314) for this insight.

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space (rather than anything in it) would be the fundamental causal principle.Thus, the transcendental realist is forced to accept SN.

5 Conclusion

The chief goal of this essay has been to argue that a version of Jacobi’s spiritualaffinity thesis is correct (whether or not this was the specific version intended byJacobi). Kant and Spinoza, I argued, hold strikingly similar views about the struc-ture of space and the structure of the representation of space. As I explained in§ 4, Kant’s views on the relationship between Spinozism and transcendental re-alism are not fully intelligible apart from Kant and Spinoza’s shared assumptionsabout the structure of space, particularly their views on the interconnected is-sues of the unity of space, its part-whole priority, the metaphysics of spatialproperties, and the laws governing these properties. This is one way in whichthe spiritual affinity thesis is of interest for understanding Kant’s transcendentalidealism.

Another reason this version of the spiritual affinity is of interest – particular-ly the second part, which concerns Spinoza and Kant’s views about the structureof the representation of space – is that it points to, and helps motivate, a partic-ular interpretation of Kant’s account of the relationship between the empirical,physical world and our representations of it. As noted in § 3, the phenomenalistreading of transcendental idealism reduces conditions and components of theformer (including space and the bodies in it) to certain subsets ofrepresentations.⁴⁹ But such a view is in tension with a natural reading ofKant’s “empirical realism”, according to which space and time are fully objectiveand thus irreducible to representations (pace Berkeley). Given the problem withthe phenomenalist reading, and given the affinity between Kant and Spinoza’sviews on the structure of space (particularly, their shared parallelism), it isworth considering a Spinozistic reading of the relation between, what onemight call, the transcendental world (consisting of the transcendental subject’srepresentations of space, time, and the places and physical objects within spaceand time) and the empirical, physical world.⁵⁰

See, for example, Van Cleve (1999, 8–12). Notice that this issue is distinct from the (much-discussed) issue of the relationship betweenthe phenomenal world and the noumenal world (the so-called two-world/one-world debate).Here the issue is about how the transcendental subject and its representations relate to theempirical, physical world described by physics. If one takes (what I am calling) the trans-cendental world to be identical with the noumenal world, then the Spinozistic interpretation is

Kantian Space, Supersubstantivalism, and the Spirit of Spinoza 59

According to this reading, which can only be briefly sketched here, the pureintuitions of the whole of space and time (the representations in their formal re-ality) and space and time themselves (the objects of these representations, i.e.,their objective reality) are equally real, irreducible, and parallel expressions ofone-and-the-same underlying reality.⁵¹ There aren’t two things: space and itspure intuition. Instead, there is just one thing, and how we describe it dependson whether we occupy the transcendental standpoint (where we are concernedwith the possibility of knowledge of an empirical world, and describe the com-ponents and conditions of this world, including space, in terms of what Spinozawould call the attribute of thinking) or whether we occupy the empirical stand-point (where we are concerned with the possibility of the empirical world itself,and describe it and its components and conditions in terms of the attribute ofextension).⁵² The same can be said for, on the one hand, the objectiveexperiences ⁵³of physical items within space and time – experiences that occurwithin the “transcendental subject” – and, on the other hand, the physical statesof affairs corresponding to those objective experiences. There aren’t two items:the objective experience of, say, a chair being next to the door, and the physicalstate of affairs of the chair being next to the door. Instead, there is one state ofaffairs, described alternately as a complex mode of thinking inhering in the tran-scendental subject and a complex mode of extension. The same can be said for,

consistent with a one-world reading. However, if one does not identify the transcendental worldwith the noumenal world (and to me at least it is far from obvious that they are identical), theSpinozistic reading I am proposing is consistent with a two-world reading. On the two-worldSpinozistic reading, the transcendental world and the empirical, physical world are one-and-the-same phenomenal reality expressed in two different ways. This phenomenal reality is, however,not itself the fundamental level of reality but is rather grounded in a more fundamental nou-menal reality. As I suggested in the footnote above, this underlying reality can be taken as a thing-in-itself(this would be a ‘one world’ version of this Spinozistic reading) but it need not be so taken by aproponent of the Spinozistic reading. On a two-world version of the Spinozistic reading, the ‘one-and-the-same underlying reality’ would simply be a metaphysically neutral (with respect toextension and thinking) phenomenal reality that is grounded in noumenal reality and has twoaspects: a representational/thinking aspect and an extended aspect. An implication of this reading is that there is just one transcendental subject, just oneintuition of space, and just one overarching objective experience in which all others are con-tained. For some evidence that Kant holds such a view, see CPR A 110. I am here contrasting the objective experience of a state of affairs (for example, a dog beingnext to a house) with subjective experiences, for example, a subject’s awareness that her per-ceptions occur to her in such-and-such a temporal order. I take the paradigms of objectiveexperiences to be the sorts of experiences of objective time-relations described in the AnalogiesChapter.

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on the one hand, the synthetic unity of apperception, which is the property ofmind responsible for the “community” among our representations leading to ob-jective experience, and, on the other hand, the property of the physical world invirtue of which all substances within it have to be in a real community with oneanother.⁵⁴ Here again, there are not two unities but rather one unity expressed indifferent ways.

On this Spinozistic reading, Kant’s transcendental idealist claim that spaceand time and the things in them are representations is not an espousal of phe-nomenalism (which Spinoza would complain collapses the attribute of extensioninto the attribute of thinking) but rather an acknowledgement of one conse-quence of the Spinozistic view: everything at the level of extension is necessarilyaccompanied by, and so inseparable from, some mode of thinking/representa-tion in the transcendental subject. (In this respect, Kant’s transcendental subjectplays the role of Spinoza’s divine intellect.) By contrast, when Kant says thatspace and time are fully real (as he does when he occupies the standpoint of em-pirical realism), he points to another consequence of the Spinozistic view: therealm of extension cannot be reduced to, or explained through, the realm ofthinking/representation. The representational and the spatial are explanatorilyself-contained expressions or aspects of the same reality. This Spinozistic viewpermits Kant to prioritize the representational aspect when giving an accountof the extent and conditions of our a priori knowledge (as Kant does when wear-ing his transcendental idealist hat). It also permits Kant to prioritize the objectiv-ity and reality of space (and that of the things in it) when giving an account ofthe structure of the physical world and the conditions of its possibility (as hedoes when wearing his empirical realist hat). It also ensures that these stand-points are complementary rather than in conflict.

One objection to the Spinozistic reading is that it is unable to accommodateKant’s views on subjective experiences, for example, an empirical subject’s expe-rience of her perception of the door of the house as occurring before her percep-tion of the roof of the house. Such experiences, it might be claimed, cannot beidentified with any states of affairs in the physical world (for example, the roof ’sexisting after the house or existing at the same time as the house). One possibleanswer to this objection is that it overlooks the most natural physical state of af-fairs to identify with such subjective experiences, which consist in a specific em-pirical subject’s succession of perceptions: a succession of physical states in aparticular human body (in particular, in a human brain).

See here CPR A 214/B 261.

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What complicates this straightforward Spinozistic answer, however, is Kant’sapparent desire to retain a form of dualism even at the empirical level: the em-pirical, physical world consists not just of human bodies interacting with otherphysical objects and with each other. For each living human body, there is alsoapparently a corresponding immaterial soul, which is causally coordinated withthat body.⁵⁵ Subjective experiences, it seems, are to be identified with successivestates of particular souls, states which are immediately caused by states of thecorresponding body (in particular, the brain), and mediately caused by otherphysical objects.⁵⁶ Now, there is some evidence to suggest that these souls arethemselves, in some sort of manner, in space.⁵⁷ If that is true, then Kant couldstill accept that every representation can be identified with something underthe attribute of extension. If it is not true that phenomenal souls are in space,then it must be admitted that Kant’s is an impure form of Spinozism: some rep-resentations, in particular, so-called subjective experiences can’t be identifiedwith anything under the attribute of extension. But we could still attribute toKant the weaker claim that every representation can be identified with somestate of affairs that is at least causally connected with things in space. Moreover,we can attribute to Kant a yet stronger claim, if we distinguish representationsinsofar as they belong to and are viewed from the standpoint of particular em-pirical selves (such are subjective experiences) from representations insofar asthey belong to and are viewed from the standpoint of the transcendental subject(such are the pure intuitions of space and time, as well as objective experiences):all the latter representations are identical with states of affairs that fall under theattribute of extension.

All of this of course falls far short of a complete explanation (much less adefense) of the Spinozistic reading. But I am hoping to have said enough togive a general sense of what such a reading would look like and to show thatit is worth exploring further. The detailed explanation and defense will haveto wait for a future time.

For Jacobi, Spinoza’s spirit was a demon to be exorcised. In claiming thatKant’s theory of space is “wholly in the spirit of Spinoza” one representativereader, Schütz, took Jacobi to be suggesting that the Critical philosophy was spi-ritually corrupted by Spinoza. But Spinoza’s system has a rigor and attractive-ness that is only beginning to be fully appreciated. The spirit of Spinoza is look-ing less demonic by the day. I have tried to show how approaching

See, e.g., CPR A 379 and A 385. For some evidence that Kant is working with this picture, see CPR A 213/B 260. See, e.g., AA 28:756–758, where Kant talks of a “virtual presence” of the soul in space.

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transcendental idealism with Spinoza’s position in view can highlight and moti-vate Kant’s own view. Kant clearly regarded some aspects of Spinoza’s positionas unacceptable (particularly, his supersubstantivalist necessitarianism) but hearguably agrees with key tenets of Spinoza’s philosophy, whether or not hewas fully conscious that they are tenets of Spinoza’s philosophy. All of thisopens up the tantalizing possibility that the German Idealists’ efforts to synthe-size Kant and Spinoza might not have been off-base.⁵⁸

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I am grateful for very helpful comments on this paper by Eric Watkins, Dan Schneider, andan anonymous reviewer for this journal.

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