Critical Idealism and Transcendental Materialism: A Speculative Analysis of the Second Paralogism

Michael J. Olson

Villanova University

Abstract: This paper argues that the critical doctrine of the necessary unity of the thinking subject propounded in Kant’s Second Paralogism contains an idealist commitment to the metaphysically exceptional nature of the unifying activity of thought.  Rather than rejecting Kant’s transcendental framework as necessarily idealist and antagonistic to the current projects of speculative materialism, it is argued that transcendental philosophy should remain an important ingredient of any contemporary metaphysics. The implicit metaphysical idealism of Kantian critical idealism, it is claimed, in the end reveals speculative resources within the architecture of transcendental philosophy that can, if I am right, maintain the importance of the project of determining the epistemological legitimacy of metaphysical knowledge without reducing metaphysics to the subjective idealism of Kantian critical philosophy.

Keywords: Kant; Paralogisms; Transcendental materialism

‘Idealism is a kind of cancer in metaphysics which until now was deemed untreatable’.[1]

This paper begins from the commitment that the project of contemporary metaphysics, which for good reason has recently rallied around the recuperation of philosophical speculation, should not abandon Kantian critical or epistemological concerns lest we restage the metaphysical battlefield properly maligned in the Preface to the first Critique as the source of the denigration of the queen of the sciences. The purpose of speculative philosophy, as Hegel rightly saw, is not to overcome epistemological questions of the possibility of metaphysical knowledge, but to construct a metaphysical architecture that can account for the intelligibility of both objects and the philosophical comprehension of those objects. Speculative philosophy, I claim, remains internally bound to transcendental philosophy and opposed to philosophical dogmatism inasmuch as it requires a moment of metaphysical self-comprehension and epistemological self-validation. That is, in addition to grounding the intelligibility of objects it must also finally ground the intelligibility of its initial act of speculative construction and so show it to be more than capricious fantasy. What separates philosophical speculation from dogmatism, then, is this retroactive epistemological validation of its initially axiomatic assertion of the speculative identity of the subject and object. This essential connection between speculative metaphysics and transcendental philosophy indicates the necessity of a continued engagement with Kantian critical philosophy even as we attempt to move beyond the correlationism he inaugurated.

The way Kant developed his method of philosophical self-criticism, however, relies on a complex of loosely idealist metaphysical presuppositions, which are in principle incapable of internal justification, and so the Kantian articulation of transcendental philosophy must be altered if it is to be reconciled with contemporary materialist convictions and metaphysical aspirations. Specifically, Kant’s critical elimination of the possibility of knowledge of things as they are in themselves, and of things that transcend first-person experiential structures more generally, relies on the claim that the unity of the categories of substance, causality, etc. cannot be applied beyond the scope of experience because the unity of conceptual knowledge (which involves at least the unification of the multiplicity of predicates contained in a concept) can only be provided by the foundational yet empty or merely logical unity of the spontaneous activity of human cognition. This empty, formal unity of cognition, which is different in kind to the external unity of composite material substances, requires that the manifold content of cognition be provided by sensibility (since the empty unity of apperception provides no content). The results of this analysis are two-fold: metaphysical research is limited to elucidating the conditions of human experience while the humble sobriety of this limitation obscures the metaphysical idealism that lies at its base.

If we accept the importance of Kant’s turn from dogmatic to transcendental philosophy for maintaining the objective validity of metaphysics while at the same time rejecting rationalist means of securing this validity in a transhistoircal divine or human exceptionalism, the task of rethinking the nature of the thinking subject takes on a considerable importance. We find just such an effort in the works of leading thinkers associated with the development of a transcendental materialism: Alain Badiou has long insisted that the cornerstone of his thought is a materialist theory of the subject[2] and Adrian Johnston, often working through the work of Slavoj Žižek, has written extensively on the relation between subjectivity and transcendental materialism.[3] When considering the nature of the subject in transcendental philosophy, the natural starting point is the analysis of the limits of our knowledge of the thinking subject, or soul,[4] found in the Paralogisms of Pure Reason. Further, when the ideality or materiality of the soul is the specific object of concern, the Second Paralogism, which addresses the rational psychologist’s claim that the soul is simple, so immaterial and incorruptible, will be the most suitable focal point of our speculative analysis of the Kantian project.

By mounting an explicitly speculative analysis of this Kantian text I will not reject the critical or epistemological character of transcendental philosophy, but will maintain it in a way that exceeds the subject-object dualism that organizes Kant’s own response to the question of the conditions of the intelligibility of the world. This transfigured transcendental philosophy will, then, no longer afford a fatal primacy to the exceptional and uncognizable human ground of synthetic unity. My gamble is that the production of the internal unity of thought, once stripped of its subjective idealism, can be rendered consistent with the real production of unity, and the subordination of metaphysical claims to the demands of epistemological validation can be maintained without lapsing into a kind of correlationism.

Kant argues forcefully in the B Deduction that the highest condition of the intelligibility of the world is the unity of conceptual representation. The minimal condition for such an intelligibility is the unification of a series of conceptual predicates with the appearance of the objects subsumed by that concept. ‘I am conscious to myself a priori’, Kant explains, ‘of a necessary synthesis of representations—to be entitled the original synthetic unity of apperception—under which all representations that are given to me must stand, but under which they have also to be brought by means of a synthesis’.[5] After establishing the necessity of the synthetic production of such a unity, the natural question is: how is this unity produced? or what produces this unity? The arguments of the Paralogisms are intended to undercut the necessarily subreptive nature of any non-critical response to such questions by preventing the objectification of subjective, transcendental conditions of objective knowledge. An examination of the Second Paralogism reveals, however, that the apparently critical prohibition against positive claims identifying the soul’s simplicity as the substantial ground for the unity of conceptual knowledge harbors an implicit idealism that must be rejected.

The Second Paralogism, which is ‘no sophistical play’, Kant admits, ‘but an inference which appears to withstand even the keenest scrutiny’ (Kant, CPR, A351), asserts ‘that if a multiplicity of representations are to form a single representation, they must be contained in the absolute unity of the thinking subject’ (Kant, CPR, A352). Kant presents the inference supporting the rational psychological doctrine of the simplicity of the soul as follows:

That, the action of which can never be regarded as the concurrence of several things acting, is simple. Now, the soul, of the thinking ‘I’, is such a being. Therefore, etc.(Kant, CPR, A351)

The major premise of the argument is simply a definition of simplicity, and so the real interest lies in the truth or falsity of the minor premise, which asserts that the soul satisfies the definition of simplicity. The rational psychologist’s argument for the truth of the minor premise attempts to extend the necessity that all thoughts can be accompanied by the ‘I think’ to a positive conclusion concerning the nature of the ‘I’ that thinks. That the unifying activity of the soul cannot be considered the coordinated activity of a multiplicity of (material) substances is supposedly shown by the internal or absolute unity characteristic of the transcendental unity of apperception. If the soul were composed of a multiplicity of substances, the argument goes, each of those substances would contain a portion of any thought that I have. ‘But this cannot be maintained’, Kant says on the rational psychologist’s behalf:

For representations (for instance, the single words of a verse), distributed among different beings, never make up a whole thought (a verse), and it is therefore impossible that a thought should inhere is what is essentially composite. It is therefore possible only in a single substance, which, not being an aggregate of many, is absolutely simple.(Kant, CPR, A352)

The necessary unity of a thought, that is, requires that the thing in which that thought inheres, the soul, possess the same absolute unity of the thought itself. The unity of a thought cannot, in other words, be produced out of a multiplicity, and so there must be a simple ground which unifies the conceptual and phenomenal manifold.

Kant begins his criticism of the Paralogism of simplicity by remarking that it is in fact the Achilles of rational psychology, which signals that he considers this argument to be the central and most powerful of this purported science of the soul. Despite his claims concerning the formal invalidity of the inference, Kant identifies the ‘nervus probandi’ of the Second Paralogism to be the truth of the minor premise: ‘if a multiplicity of representations are to form a single representation, they must be contained in the absolute unity of the thinking subject’ (Kant, CPR, A352). The question at hand is whether the soul is in fact the kind of thing identified in the major premise: a thing whose activity can never be regarded as the concurrence of the activity of several things. Kant’s analysis of the Paralogism challenges the rational psychologist’s ability to prove the truth of this premise. The Paralogisms as a whole, accordingly, attempt to curb the dogmatic inclination to develop the transcendental necessity of apperception into a speculative metaphysics of the soul by insisting that there is no possible legitimate proof of the substantiality, simplicity, or personality of the soul.

The development of this negative or disciplinary function of the critical engagement with rational psychology relies on a distinction that Kant introduces only after addressing the four Paralogisms individually. Toward the end of the A Paralogisms he distinguishes between dogmatic, critical, and skeptical objections. Dogmatic and skeptical objections direct themselves toward the content of the proposition in question. A dogmatic objection ‘requires an insight into the nature of the object such that we can maintain the opposite of the what the proposition has alleged in regard to this object’ (Kant, CPR, A388). The materialist objection to the second Paralogism, for example, which rejects the impossibility of considering the activity of the soul as the concurrence of the activities of a multiplicity of substances, asserts a more accurate insight into the object itself (the soul), and on that basis, rejects the rational psychologist’s conclusion. A skeptical objection, relies on a similar dogmatic familiarity with the object, but argues in such a way that the assertion of the proposition and the counter-assertion of the dogmatic objection have equal weight, which shows ‘that all judgment in regard to the object is completely null and void’ (Kant, CPR, A389). A critical objection, on the other hand, is not directed toward the content of the proposition, but toward its purported proof. Such an objection, Kant explains, ‘since it leaves the validity or invalidity of the proposition unchallenged, and assails only the proof, does not presuppose fuller acquaintance with the object or oblige us to claim superior knowledge of its nature; it shows only that the assertion is unsupported, not that it is wrong’ (Kant, CPR, A388). Kant’s analysis of the Paralogisms restricts itself to such a critical operation. He accordingly criticizes a series of possible proofs that the soul is in fact the kind of thing whose activity cannot be considered to be the concurrence of the activity of a collection of discrete substances and exposes the weakness of these proofs in turn. The truth of the minor premise of the second Paralogism cannot, Kant argues, be proven through concepts alone (that is, analytically), through experience (that is, synthetically), or by inference from experience.

An analytic proposition is, for Kant, characterized by the containment of the predicate within the subject,[6] and so the principle of all analytic propositions is the principle of contradiction.[7] An analytic proof for the simplicity of the soul must, then, show that the concept of the unity of representation contains within itself the predicate of its simple ground.[8] Such a proof is impossible, however, ‘For the unity of the thought, which consists of many representations, is collective, and as far as mere concepts can show, may relate just as well to the collective unity of different substances acting together (as the motion of a body is the composite motion of all its parts) as to the absolute unity of the subject’ (Kant, CPR, A353). The concept of the unity of a thought does not in itself contain any reference to the simple or composite nature of the thing whose activity unifies the thought, and so the simplicity (or multiplicity) of the soul cannot be proven using concepts and the principle of contradiction alone. But neither can the proof of the premise be proven through experience.

Kant’s objection to any proof of the simplicity of the soul through experience proceeds along two lines. First, he notes that the proper modality of judgments of experience is actuality, not necessity. Even if experience did furnish evidence of the simplicity of the soul, that would not establish the necessity of such simplicity.[9] Second, and more interestingly, Kant argues that the unity of a thought can only be thought in the first person. I cannot, that is, think the unity of a thought that is not mine. He writes, ‘It is obvious that, if I wish to represent to myself a thinking being, I must put myself in his place, and thus substitute, as it were, my own subject for the object I am seeking to consider (which does not occur in any other kind of investigation)’ (Kant, CPR, A353-354). A thinking being, unlike any other being, can only be considered from the perspective of that being. Why this is the case is not nearly as obvious as Kant asserts it is, however. Surely cognitive neuroscience is explicitly engaged in the investigation of thinking beings as objects; how, then, does Kant defend this position?

In the introductory remarks to the Paralogisms he explains more generally that ‘It [‘I’] is known only through the thoughts which are its predicates, and of it, apart from them, we cannot have any concept whatsoever, but can only revolve around in a perpetual circle, since any judgment upon it has always already made use of its representation’ (Kant, CPR, A346/B404). When I think the necessary unity of representations in cognition in general, that is, when I attempt to take the ‘I think’ as the object of my thought, the unity of the object of that thought is conditioned by a more primary unity of the form of my own thought. Kant makes a similar point in the B Paralogisms, writing ‘The subject of the categories cannot acquire a concept of itself as an object of the categories. For in order to think them its pure self-consciousness, whish was to be explained, must itself be presupposed’ (Kant, CPR, B422). Insofar as I think the ‘I think’, another ‘I’, which is not the object of that thought, is necessarily at work. This elusive character of the ‘I’, its inability to be successfully objectified by thought, indicates, according to Kant, that the necessary unity of the soul is an exclusively subjective condition of experience, which one cannot, in principle, render objective. The ‘I think’ ‘is not itself an experience, but the form of apperception which belongs to and precedes every experience’ (Kant, CPR, A354). Since the absolute unity of the ‘I’ is not itself an object of experience, but the condition of experience, there is no possible proof of the simplicity of the soul through experience.

Having eliminated proofs from both concepts and experience, Kant finally argues that one cannot prove the simplicity of the soul through inference. The simplicity of the soul as a real object is not the result of logical inference from the bare ‘I think’. Rather, Kant says, ‘The proposition, ‘I am simple’, must be regarded as an immediate expression of apperception, just as what is referred to as the Cartesian inference, cogito, ergo sum, is really a tautology, since the cogito (sum cogitans) asserts my existence immediately’ (Kant, CPR, A354-355).[10] This marks a transition in Kant’s remarks on the Paralogism. Whereas the previous two objections—to possible proofs through concepts and experience—focused on the fruitlessness of speculation concerning the real simplicity of the soul, Kant now addresses the true meaning of the simplicity of the ‘I think’.[11] The simplicity immediately contained in the necessarily subjective proposition ‘I think’ is not real or objective, but logical or transcendental.

Having argued for the impossibility of proving the real simplicity of the soul either analytically through concepts or synthetically through experience, Kant concludes that the unity of the ‘I think’ has neither intelligible nor empirical validity, but is merely transcendentally legitimate. ‘This much, then, is certain’, Kant explains, ‘that through the “I”, I always entertain the thought of an absolute, but logical, unity of the subject’ (Kant, CPR, A356). If the ‘I’ were not an absolute unity, it would be possible for me to have thoughts I would not know to be my thoughts. This, according to Kant, is absurd. ‘It does not, however, follow’, Kant continues, ‘that I thereby know the actual simplicity of my subject’ (Kant, CPR, A356). As he argued concerning proofs from experience, the ‘I’ can never be an object of experience, and so no objective judgments concerning its simplicity are possible. Summarizing the results of his reflection on the legitimate meaning of the unity of apperception, Kant writes:

I may legitimately say: ‘I am a simple substance’, that is, a substance the representation of which never contains a synthesis of the manifold. But this concept, as also the proposition, tells us nothing whatsoever in regard to myself as an object of experience, since the concept of substance is itself used only as a function of synthesis, without any underlying intuition, and therefore without an object. It concerns only the condition of our knowledge; it does not apply to any assignable object’.(Kant, CPR, A356)

Taken transcendentally, that is as the condition of cognition, the soul can only be regarded as a simple unity; taken as an object of philosophical or theological speculation, however, there are no grounds for positively establishing either the simplicity or multiplicity of the soul. This result of Kant’s criticism of the Paralogism, importantly, does not establish the falsity of the rational psychologist’s claim. Such a falsification would be dogmatic. Instead it indicates the lack of support for that position. The absence of theoretical support for a position does not, however, indicate its absurdity, and there might in fact be good practical reasons for maintaining an unprovable theoretical position. Accordingly, Kant concludes his remarks on the second Paralogism by considering the possible pragmatic value of assuming the objective simplicity of the soul.

The prima facie virtue of the doctrine of the real simplicity of the soul is the soul’s substantial difference from matter and consequent incorruptibility. If the simplicity of the soul can be neither proved nor disproved theoretically, there might, then, be practical reasons for maintaining its objective validity.[12] The spatiality of matter guarantees that it can be divided, and so any particular material body is subject to the possibility of material corruption and dissolution. If the soul is not distinct from matter, then, its immortality cannot be proven. Kant argues, however, that even if we assume the real simplicity of the soul, ‘we still cannot make the least use of this proposition in regard to the question of its dissimilarity from or relation to matter’ (Kant, CPR, A357). Referring to the result of the Aesthetic Kant remarks that bodies or matter are objects of outer sense and not things in themselves; the soul, on the other hand, is an object of inner sense, and so cannot be material. ‘This is equivalent to saying’, he explains, ‘that thinking beings, as such, can never be found by us among outer appearances, and that their thoughts, consciousness, desires, etc., cannot be outwardly intuited. All these belong to inner sense’ (Kant, CPR, A357). The soul can be distinguished from empirical matter as an object of outer sense, then, without appeal to the assumption of the simplicity of the soul.

Further, it is possible that the transcendental substrate of empirical matter is identical with the soul. Despite the phenomenal difference between objects of inner and outer sense, it remains possible that their noumenal grounds might nonetheless be identical. The assumption of the simplicity of the soul is insufficient to distinguish it from matter considered as a transcendental object, and so cannot prove the soul’s immortality. Kant writes:

I can therefore very well admit the possibility that it is in itself simple, although owning to the manner in which it affects our senses it produces in us the intuition of the extended and so of the composite. I may further assume that the substance which in relation to our outer sense possesses extension is in itself the possessor of thoughts and that these thoughts can by means of its own inner sense be consciously represented.[13](Kant, CPR, A359)

Any potential moral or pragmatic benefits we thought might issue from assuming the simplicity of the soul absent of any positive proof, then, are only illusory. Even if the soul were objectively and not only logically simple, it could still be basically similar to matter, and so subject to corruption and dissolution.[14]

Kant refutes both idealist and materialist accounts of the real constitution of the thinking subject in the Second Paralogism, as we have seen, by arguing for the impossibility of proving either the simplicity of multiplicity of the soul. The minor premise of the Paralogism, that is, cannot be proven true by any argumentative strategy Kant can identify. The critical idealist position requires that the highest condition of the intelligibility of the world, the unity of apperception, can only be thought as a condition of thought and cannot itself be a legitimate object of knowledge. Although we know that all thought must be brought under the absolute unity of the thinking self, we cannot determine what the nature of the real ground of that unity is. The consequences of this necessary agnosticism concerning the real substrate of thought for the possibility of a materialist articulation of transcendental philosophy have not, however, been universally recognized. There are scholars who argue in a functionalist vein that knowledge of the necessary activity of the soul does not provide knowledge of the ultimate subject of that activity, and that this separation, which is at the heart of the Paralogisms, does not challenge but in fact supports a reconciliation of Kant’s critical idealism with the materialism of much contemporary philosophy of mind and cognitive neuroscience.[15] I maintain, however, that, although accepting the argument of the Second Paralogism secures us against the idealist thesis of the simplicity and immateriality of the soul, Kant’s solution remains tacitly idealist. This idealism is manifested in two interrelated hallmarks of anti-materialist thought, which I will only briefly mention. First, the argument analyzed above concerning the impossibility of taking the thinking self as an object of knowledge without simultaneously displacing it as the subject of that same knowledge effectively reinscribes the Platonic and Cartesian dualism of thought and matter within the transcendental architecture. The translation of this dualism into Kant’s transcendental position results in the conclusion that the highest condition of the intelligibility of the world is in fact different in kind than the world whose intelligibility it renders possible. No materialism can accept such a position. If transcendental philosophy is capable of supporting a genuine materialism, then, this conclusion must be circumvented. A transcendental materialism must conclude that the conditions of the intelligibility of the world do not transcend that world but are ultimately rooted in it. The second hallmark of idealism implicit with the critical dissolution of the Paralogism hinges on the distinction between our consciousness of the necessary unifying activity of the self in the absence of any possibility of genuinely cognizing that self, on the one hand, and the cognizability of the natural world. We find this same structure, in which we are consciously familiar with the ground of the possibility of cognition despite our inability to cognize it, in Berkeley distinction between spirits and ideas.[16] We certainly cannot saddle critical idealism with the weight of Berkeley’s metaphysical idealism on the basis of this structural similarity alone. The primary effect of this distinction within the transcendental idealist framework, however, is that there is an insuperable rift between the transcendental subject of knowledge and the material world as objects of possible knowledge. It is in principle impossible, within the confines of critical idealism, to understand the process of the natural emergence or development of our faculties of cognition. The conditions of the possibility of knowledge cannot be thought within the categories of history. If transcendental philosophy is to become materialist, then, it must be shorn of its implicit subject-object dualism, and accompanying human exceptionalism, and its purported immunity to historical analysis.

In order to excise the implicit metaphysical idealism within the Second Paralogism and to advance the cause of a transcendental materialism, then, I will now outline the development of a speculative potential contained within the Paralogism. Much work remains to be done on this front, and rendering transcendental philosophy fully materialist requires attention to elements of the Critique of Pure Reason not addressed at all here,[17] so these remarks should be recognized as the mere outline of a much larger research program. My speculative response has the perhaps peculiar character of accepting Kant’s arguments against both idealist and materialist attempts to determine the real substrate of thought. Rather than rejecting his arguments against the materialists, I will suggest a speculative method of establishing the multiplicity, and so materiality, of the ground of the unity of thought. To this end I will attempt to indicate how the system of critical idealism is altered when, rather than accepting the impossibility of determining the truth or falsity of the minor premise of the Second Paralogism, we affirm its falsity. I will speculatively assert, for the time being, that the unifying activity of the soul can in fact be considered to be the result of the coordinated activity of a multiplicity of substances. Then, following the speculative logic mentioned above, I will explain how this speculative assertion might come to retrospectively validate the truth of what is initially only an assertion.

If it is shown to be possible for a composite to produce the internal unity that characterizes conceptual knowledge, then we have, at the very least, undermined a central pillar of Kant’s subjective idealism. The highest condition of the intelligibility of the world, the synthetic unity of conceptual and intuitive representation together with the structurally guaranteed non-corporeality of the source of that unity necessitates the idealism of Kantian transcendental philosophy. Absent any real or material ground for the internal unity of thought, the condition not only of knowledge but of the possibility of knowledge, which is to say of the intelligibility of the world itself, must lie within the transcendentally ideal structures of thought. This is of course Kant’s deep idealism: the intelligibility or lawful regularity of the world itself is conditioned by the synthetic activity of the thinking subject. If the synthetic activity of transcendental subjectivity is a special case of the emergence of absolute, logical unity from material multiplicity, however, a transcendental subordination of metaphysics to the conditions of the possibility of knowledge need not amount to asserting the dependence of the real intelligibility of the world on human thought. The transcendental unity of apperception, in other words, need not, in this case, be the seat of transcendental philosophy’s human exceptionalism; it may instead be one of many instances of a more general production of ideal unity on the basis of real multiplicity.

Given the possibility of the transcendental identity of the activities of thought and matter, and the impossibility of non-dogmatically determining the reality of the material ground of thought, we would do well to move beyond the opposition between dogmatism and criticism. If we simply assert the capacity of material substance to generate logical unity we will not have advanced beyond the Kantian problem, we would have merely ignored the critical injunction against dogmatic assertions. There is another option available, however: we can assert the possibility of the material constitution of the unity of the ‘I think’, and so clear the way for the conclusion that the activities of thought and matter are actually and not merely possibly predicates of the same transcendental subject, and then, drawing out the consequences of this speculative decision within the larger critical architecture, retrospectively justify our initially dogmatic assertion. The critical rejection of a materialist theory of the subject might be effectively excised, that is, through speculation. This amounts to offering a method of proof not considered by Kant in his criticism of the Paralogism. We recall that Kant shows the impossibility of proving the simplicity of the soul through concepts alone, through experience, and through inference. The speculative advance, which I am only sketching here, does not directly prove the composite nature of the soul and then proceed to deduce the metaphysical identity of the substrate of thought and matter. Rather, it assumes that, under certain conditions, material composites can produce the logical unity characteristic of apperception, and, on the basis of this assumption, develops an alternative deduction of the objectively valid deployment of the categories of knowledge that can retrospectively provide an epistemological validation of the original speculative assumption. Kant may be correct that a direct proof of the simplicity or composite nature of the soul is impossible, but his critical rejection of any positive doctrine of the nature of the thinking subject might nonetheless be overcome by such an indirect method of argumentation. I will now conclude by very briefly sketching how this speculative recuperation of the epistemological justification of the otherwise dogmatic assertion that multiplicities can produce the logical unity characteristic of apperception might work.

The limitation of knowledge claims to those possible on the basis of first-person experience and the concomitant elevation of human thought to the highest condition of the intelligibility of the world rest, as I have argued, on the inability to know whether composites can produce the internal unity of representations. The limitation of conceptual intelligibility to the field of sensible intuitions, which is the ultimate critical justification for the impossibility of knowing the real identity of thought and world, relies on the conclusion that knowledge is a certain combination of multiplicity and unity, the multiplicity of the sensible manifold and the unity of its conceptual intelligibility. The transcendental unity of the synthetic activity of thought, precisely because it is not a multiplicity[18] cannot provide the manifold it unifies, and so the intelligible structures of the categories can only be applied legitimately to the sensible manifold provided by intuition.[19] Knowledge is limited to possible objects of sensible experience, then, because the source of the formal unity of knowledge cannot itself provide the manifold content it unifies. The formal unity of the self, precisely because of its logical simplicity, cannot, on Kant’s account, provide the content of its cognitions, and so must receive it through perception. If the ground of the unity of representations is itself multiple, however, there is an internal connection between the formal unity and sensible manifold of conceptual knowledge in this material composite itself. Categorial knowledge need not, then, be limited to the realm of sensible experience because the manifold content of knowledge (as well as its formal unity) both stem from the material condition of the intelligibility of the world. All knowledge need not, then, be knowledge of objects of sensible experience, and the limits of transcendentally authorized metaphysics can be considerably redrawn.

Specifically, once first-person sensible experience is compromised as a necessary condition of knowledge, it is no longer in principle impossible to prove the identity of the subjects of intellectual and corporeal activity. By initially assuming that the activity of composite substances can produce the internal unity necessary for knowledge, then, we can alter the metaphysical prohibitions of the critical edifice such that this dogmatic assumption, which still acts as a condition for the possibility of knowledge, can itself become an object of possible knowledge. This dogmatic gamble, then, is—or at least might be; the details of an alternate Deduction remain to be worked out—retroactively legitimated by the epistemological structures that it authorizes. The implicit metaphysical idealism of Kantian critical idealism, I claim, in the end reveals speculative resources within the architecture of transcendental philosophy that can, if I am right, maintain the importance of the project of determining the epistemological legitimacy of metaphysical knowledge without reducing metaphysics to the subjective idealism of Kantian critical philosophy.

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