Among Immanuel Kant’s (1724–1804) most influentialcontributions to philosophy is his development of the transcendentalargument. In Kant’s conception, an argument of this kind beginswith a compelling premise about our thought, experience, or knowledge,and then reasons to a conclusion that is a substantive and unobviouspresupposition and necessary condition of this premise. The crucialsteps in this reasoning are claims to the effect that a subconclusionor conclusion is a presupposition and necessary condition of apremise. Such a necessary condition might be a logically necessarycondition, but often in Kant’s transcendental arguments thecondition is necessary in the sense that it is the only possibleexplanation for the premise, whereupon the necessity might be weakerthan logical. Typically, this reasoning is intended to beapriori in some sense, either strict (Smit 1999) or more relaxed(Philip Kitcher 1981, Pereboom 1990). The conclusion of the argumentis often directed against skepticism of some sort. For example,Kant’s Transcendental Deduction targets Humean skepticism aboutthe applicability ofa priori metaphysical concepts, and hisRefutation of Idealism takes aim at skepticism about external objects.These two transcendental arguments are found in theCritique ofPure Reason (1781, 1787), but such arguments are found throughoutKant’s writings, for example in theGroundwork of theMetaphysics of Morals (1785), in theCritique of PracticalReason (1788), in theCritique of the Power of Judgment(1790), and in theOpus Posthumum (1804; Förster 1989).This article focuses on the Transcendental Deduction, the Refutationof Idealism, and more recent transcendental arguments that areinspired by Kant’s work.

• 1. The Transcendental Deduction
  • 1.1 Apperception and its Unity
  • 1.2 Representations of Objects and the Single-Substantive-Premise Interpretation of the B-Deduction
  • 1.3 Universality and Necessity in our Experience of Objects
  • 1.4 Logical Forms of Judgment and the Categories
  • 1.5 The Second Step of the B-Deduction
• 2. The Refutation of Idealism
• 3. Contemporary World-Directed Transcendental Arguments
• 4. Contemporary Practical Transcendental Arguments
• 5. Concluding Remarks
• Bibliography
  • Primary Literature
  • Secondary Literature
• Academic Tools
• Other Internet Resources
• Related Entries

1. The Transcendental Deduction

The Transcendental Deduction (A84–130, B116–169) isKant’s attempt to demonstrate against empiricist psychologicaltheory that certaina priori concepts correctly apply toobjects featured in our experience. Dieter Henrich (1989) points outthat Kant’s use of ‘Deduktion’ redeploysGerman legal vocabulary; in Holy Roman Empire Law,‘Deduktion’ signifies an argument intended toyield a historical justification for the legitimacy of a propertyclaim. In Kant’s derivative epistemological sense, a deductionis an argument that aims to justify the use of a concept, one thatdemonstrates that the concept correctly applies to objects. For Kant aconcept isa priori just in case its source is theunderstanding of the subject and not sensory experience (A80/B106;Strawson 1966: 86). The specifica priori concepts whoseapplicability to objects of experience Kant aims to vindicate in theTranscendental Deduction are given in his Table of Categories(A80/B106); they are Unity, Plurality, and Totality (the Categories ofQuantity); Reality, Negation, and Limitation (the Categories ofQuality); Inherence and Subsistence, Causality and Dependence, andCommunity (the Categories of Relation), and Possibility-Impossibility,Existence-Nonexistence, Necessity-Contingency (the Categories ofModality).

David Hume in effect denies that a deduction can be provided for anumber of metaphysical concepts –ideas, in histerminology – including the ideas of personal identity, ofidentity over time more generally, of the self as a subject distinctfrom its perceptions, and of causal power or force (1739, 1748). InHume’s view, a concept can only be validated by finding asensory experience, that is, animpression, in particular theone that is the ‘original’ of that idea, which mustresemble that idea. But because, for example, any attempt to find animpression of causal power turns out to be fruitless, Hume concludesthat this idea does not legitimately apply (1748: §7). InKant’s terminology, Hume is determining whether one mightprovide anempirical deduction of the concept of causal power(A85/B117), and from the failure of the attempt to do so, he concludesthat this concept lacksobjective validity, that is, it doesnot apply to the objects of our experience.

Hume’s position on the deducibility ofa priorimetaphysical concepts is Kant’s quarry in the TranscendentalDeduction. But Kant concurs with Hume’s proposal that noempirical deduction can be supplied for such concepts. Instead, hesets out to provide a different sort of justification for their use,one that istranscendental rather than empirical. Such atranscendental deduction begins with a premise about any possiblehuman experience, a premise to which reasonable participants in thedebate can be expected initially to agree, and then contends that apresupposition and necessary condition of the truth of that premise isthe applicability of thea priori concepts in question to theobjects of experience. Kant’s Transcendental Deduction featuresa number of component transcendental arguments. Each begins with apremise either about the self-attributability of mental items,apperception, or else a premise about the necessity anduniversality of some feature of our experience of objects. Kant’strategy is to establish a theory of mental processing,synthesis, by arguing that its truth is a necessary conditionfor the truth of such a premise, and then to show that theapriori concepts at issue – the categories – have anessential role in this sort of mental processing. On a metaphysicalidealist interpretation of his position, the objects of experienceresult from this mental processing, and it is due to the role that thecategories have in this processing that they correctly apply toobjects. In the Transcendental Deduction Kant would thus intend tosecure a normative claim, that the categories correctly apply to theobjects of our experience, by establishing a psychological theory(Henrich 1989; Patricia Kitcher 1990: 2–29; for information onrelated argumentative strategies in Kant’s historical context,see Kuehn 1997 and Dyck 2011). The Transcendental Deduction presentsgeneral considerations supporting the applicability of all thecategories to the objects of our experience; it does not concentrateon the applicability of specific categories. This more focused task istaken up in various sections of the Analytic of Principles(A130–235/B169–287).

In theMetaphysical Deduction (A66–83, B92–116)Kant intends to derive the categories from the specific modes or formsof any human thought about the world, thelogical forms ofjudgment. The Metaphysical Deduction has an essential role toplay in the Transcendental Deduction, and we will discuss thisargument at an appropriate juncture (when we reach §19 of theB-Deduction).

For Kant, the most significant rival theory of mental processing isthat of his target, Hume. Hume concurs that a theory of experiencerequires an account of the processing of mental items, but he deniesthat such an account demandsa priori concepts or issues intheir legitimate applicability to experience. According to his theory,associationism, our mental repertoire consists solely ofperceptions, all of which are sensory items – the more vividimpressions, which constitute sensory experience, and their less vividcopies, the ideas, which function in imagination, memory, reasoning,and conceptualization (1748, §§2, 3). Association is theprocess by which these perceptions are related and ordered. Asignature feature of association on Hume’s view is that itrequires no resources distinct from the perceptions themselves. Howperceptions are ordered is solely a function of what perceptions alonecan provide. Significantly, a subject not constituted solely ofperceptions has no role in Hume’s theory; the Humean subject isjust a collection of perceptions (1739: I, IV, vi). These last twofeatures in particular make Humean associationism a highly economicaltheory, which provides it with an initial advantage over Kant’smore complex view. However, Kant contends that associationism cannotaccount for the facts to which the premises of the TranscendentalDeduction appeal, and that synthesis bya priori concepts,that is, the categories, is required in addition.

Kant characterizes synthesis as “the act of putting differentrepresentations together, and grasping what is manifold in them in onecognition” (A77/B103); it is a process that “gathers theelements for cognition, and unites them to form a certaincontent” (A78/B103). Synthesis takes multiple representations– in Kant’s terminology, a ‘manifold’ –and connects them with one another to produce a single furtherrepresentation with cognitive content (Patricia Kitcher 1990, 2011).This process employs concepts as modes or ways of orderingrepresentations. A claim critical to the Transcendental Deduction isthat it is the categories by means of which manifolds of ourrepresentations are synthesized. Since the understanding of thesubject is the source of the categories, and also a faculty thatyields synthesis, the subject plays a crucial role in mentalprocessing. It is important for Kant’s view on mental processingthat this subject is distinct from its representations, and this isanother respect in which it differs from Hume’s theory.

This discussion will focus on the Transcendental Deduction in thesecond edition of theCritique of Pure Reason (1787) –theB-Deduction – thoroughly rewritten and rethoughtrelative to theA-Deduction of the first edition (1781). Onmy reading, in §§16–20 of the B-Deduction Kant employsa two-pronged strategy for defeating associationism and establishingsynthesis. The first, contained in §§15–16, isdesigned to show that association cannot account for an aspect ofone’s consciousness of one’s self that Kant refers to asthe consciousness of its unity, and that synthesis isrequired to provide this explanation. This type of argument he callsanargument from above, signifying that it begins with apremise about self-consciousness. Correlatively, in§§17–20 we find anargument from below, bywhich Kant intends to establish that synthesis by means of thecategories is needed as a necessary condition of how we representobjects (the above/below terminology is derived from A119; forrelevant historical background, see Carl 1989, 1992). On several otherreadings, as we shall see, the B-Deduction is a more unified argument.There are reasons to accept and reasons to resist interpretations ofthis kind.

1.1 Apperception and its Unity

The argument from above in §16 can be divided into two stages.The goal of the first is to establish the various components ofthe principle of the necessary unity of apperception. Thesecond stage aims to show that synthesis is a necessary condition forthe aforementioned aspect of self-consciousness, which this principlehighlights.Apperception is the apprehension of a mentalstate – a representation, in Kant’s terminology – asone’s own; one might characterize it as the self-ascription orself-attribution of a mental state (Strawson 1966: 93–4). InKant’s conception, my apperception hasnecessary unitysince all of my representationsmust be grounded “inpure apperception, that is, in the thoroughgoingidentity ofthe self in all possible representations” (B131–2,emphasis mine). By this he means that:

(The principle of the necessary unity of apperception) Itmust be the case that each of my representations is such that I canattribute it to my self, a subject which is the same for all of myself-attributions, which is distinct from its representations, andwhich can be conscious of its representations (A116, B131–2,B134–5).

One might note three aspects of the meaning of this principle. First,as pointed out earlier, Kant maintains that the apperceiving subjectis not itself a collection of representations. Kant affirms that Ihave no inner intuition of the subject (e.g. B157), and this claimwould conflict with the subject’s being a collection ofrepresentations, since he holds that I can intuit my representationsby inner sense (e.g. A33/B49). Also, in §16 Kant remarks:“through the ‘I’, as simple representation, nothingmanifold is given; only in intuition, which is distinct from the‘I’, can a manifold be given” (B135). If he believedthe apperceiving subject to be a collection of representations, itwould be surprising for him to deny that anything manifold is giventhrough my representation of it. Second, my ability to attributerepresentations to myself as subject of them ispure, asopposed toempirical apperception. This means that I havethis ability not in virtue of Humean inner perception, or Kantianinner intuition, but rather independently of any such empiricalfaculties. However, Kant repeatedly affirms that the purity of thisapperception does not imply that the subject to which one’srepresentations can be attributed is intuited – represented asan object – in a purely rational ora priori way (e.g.,B406–9). Third, Kant states that pure apperception isoriginal, and the explication he provides is that “itis that self-consciousness which, while generating the representation‘I think’ … cannot itself be accompanied by anyfurther representation” (B132). I cannot have an intuition orany other type of representation of myself as apperceiving subjectother than by way of ‘I think…’-type thoughts, andhence these thoughts are the original representations of this subject(e.g., A350). At the same time, by virtue of my capacity forapperception, I can have a kind of propositional grasp of theapperceiving subject; Kant affirms that in apperception, I amconsciousthat I exist as subject (B157). (For recentextensive discussions of Kant on self-knowledge, see Rosefeldt 2000,Kitcher 2011, and Longuenesse 2017; cf. Howell 2001.)

Kant initiates the first stage of the argument in §16 byclaiming:

It must be possible for the ‘I think’ to accompany all myrepresentations; for otherwise something would be represented in mewhich could not be thought at all, and that is equivalent to sayingthat the representation would be impossible, or at least would benothing to me. (B131–32)

On one interpretation, the sense in which a representation would beimpossible or nothing to me if it could not accompanied with the‘I think’ is simply that I could not then become consciousof it (Guyer 1987: 139–44). It is credible that for anyrepresentation of which I am conscious, I can attribute it to myselfas subject, assuming my mental faculties are in working order, and ifno controversial account of the nature of the subject is presupposed.However, the claim that I can become conscious ofeach of myrepresentations, and that it is therefore possible for me attributeeach of them to myself as their subject, is likely false. Plausibly,some of my representations are so thoroughly subconscious that Icannot attribute them to myself, while they are nevertheless mine dueto the causal relations they bear to other representations and toactions that are paradigmatically mine. Fortunately, however, thepremise that each of my representations is such that I can attributeit to myself is not crucial for the argument from above. Rather, thepremise Kant ultimately singles out is less committed, and focusesmore specifically on the identity or sameness of the subject ofdifferent self-attributions, and my being conscious of thisidentity.

A number of interpreters, including Robert Howell (1992) and James vanCleve (1999), maintain that the argument of §16 requires apremise affirming the possibility of my beingsimultaneouslyconscious of the multiple elements of my representations, and that theimplausibility of this premise jeopardizes the soundness of theargument. Howell’s specific objection is that Kant does notestablish the following crucial premise:

(S) All of the elements of the manifold ofi (wherei is some arbitrary intuition) are such that H is or canbecome conscious, in thought, that all of those elements, takentogether, are accompanied by theI think.

(S) asserts that all of the individual elements of the selectedintuition are such that the subject is or can become conscious of themsimultaneously. In Howell’s interpretation, only if the elementsof an intuition together and at the same time are accompanied by thesameI think will it be plausible that the subject mustsynthesize these elements (Howell 1992: 162). On van Cleve’sreading, it is required that for any intuition that I have, I actuallybecome simultaneously conscious of its elements. If thisco-consciousness were just merely possible, Kant could only concludeis that the resulting representation is only possibly subject to thecategories (van Cleve 1999: 84). On an interpretation of this type,the mechanism of the argument of §16 is to adduce a kind of unityor combination that my representations actually exhibit, and then toargue that this unity requires synthesis by means of the categories asa condition or for its explanation. Kant is thus read as contendingthat actual co-consciousness is a type of unity that demands synthesisby means of the categories, and that any variety of unity short ofco-consciousness will be inadequate to establishing this objective ofthe Deduction.

Howell points out that (S) contrasts with a weaker claim:

(W) Each element of the manifold ofi is such that H is orcan become conscious, in thought, that theI thinkaccompanies that element. (Howell 1992: 161)

which allows that the individual elements of the intuition are suchthat the subject can only become conscious of each separately, perhapsin turn. He contends, however, that the unity expressed by (W) isinsufficient to generate this need for synthesis. If I am merely(possibly or actually) serially conscious of the elements of anintuition, it won’t be required that I synthesize them into aunified intuition. Howell goes on to argue that while (W) is credible,Kant cannot in fact establish (S); it is implausible that suchco-consciousness for any arbitrary intuition is actual or evengenuinely possible for us. Consequently, the soundness of thisargument, and the overall argument of the B-Deduction isimperiled.

However, it may be that only the weaker premise (W) is required forthe success of the argument of §16. First, although theco-consciousness premise (S) might besuggested in §16by the following text:

That relation comes about, not simply through my accompanying eachrepresentation with consciousness, but only in so far as I conjoin onerepresentation with another, and am conscious of the synthesis ofthem. (B133)

that claim is not uncontroversially made here. For by the assertionthat I “am conscious of the synthesis of them,” i.e., ofthese representations, Kant may mean only that I am conscious thatthey stand in a certain intimate relation to one another, forinstance, that that they are integrated with each other in a waydistinct from how mine are integrated with yours, which does notrequire co-consciousness (Pereboom 1995).

Moreover, it might well be that the argument of §16 features asubtlety that obviates the need for actual co-consciousness. The textindicates that the argument crucially turns on the claim that onlya priori synthesis – that is, synthesis byapriori concepts – can explainhow I might represent theidentity of my apperceptive consciousness (B133) orhow Imight represent the identity of the apperceiving subject (B135)for different elements of the manifold of intuition to which I canattach theI think. The inadequacy Kant claims for“empirical consciousness,” that is, for consciousnessaccording to Humean psychological theory, is that “it is initself dispersed (an sich zerstreut) and without relation tothe identity of the subject (und ohne Beziehung auf dieIdentität des Subjects)” (B133). One implication ofthis passage is that Hume’s theory does not have the resourcesneeded to explain how I can self-attribute various of myrepresentations or their elements to a subject that is both consciousof them and the same subject for each act of their self-attribution.This objection does not beg the question in Kant’s dispute withHume, since it assumes only a claim that uncommitted and reasonableparticipants in this discussion would not want to initially deny, thatthe conscious subject of these apperceptive self-attributions is thesame. Hume’s theory lacks the resources to account for thisidentity. Hume himself provides no account of apperception, butpossibilities for a Humean account are that apperceptive consciousnessamounts to perceptions that are intrinsically self-conscious, or elseconsists in perceptions of perceptions. But intrinsicallyself-conscious perceptions would be distinct from one another, aswould perceptions of perceptions; and thus they too would be“dispersed” (B133), and share no common element. Humemight propose to explain our sense of the identity of the conscioussubject of different self-attributions by the intrinsicallyself-conscious perceptions or the perceptions of perceptions beingcomponents of a single causally coherent bundle. However, this bundlewould not itself be conscious of perceptions. Consciousness ofperceptions would instead be an intrinsic feature of an individualself-conscious perception or a feature of individual perceptions of aperception. In Kant’s conception, by contrast, accounting forour sense of the identity of the conscious subject of differentself-attributions requires that this subject be distinct from itsrepresentations.

The second stage of the argument of §16 highlights anotherimplication of the claim that “the empirical consciousness,which accompanies different representations, is dispersed and withoutrelation to the identity of the subject” (B133): thatHume’s theory lacks the resources to account for myrepresentation-relation to the identity of the subject; thatis, this view cannot explain how I can “represent to myself theidentity of the consciousness in [i.e. throughout] theserepresentations” (B133) (for an opposing view see Dickerson2004: 95–8). We might imagine several kinds of explanation formy representation of this identity. One candidate is that inner senseallows me to represent this identity: the way I represent the samenessof the subject is akin to how I commonly represent the identity overtime of ordinary objects – by a cognitive sensitivity tosimilarities among the intrinsic properties represented. However, Kantand Hume concur that this is not how I might represent the identity ofthe apperceiving subject, since they agree that by inner sense Icannot represent any intrinsic properties of such a subject. A secondkind of explanation, which Kant endorses, is that I have an indirectway of representing this identity. This representation must insteaddepend on my apprehending a feature of my representations (or elementsof them) (Allison 1983: 142–4; Guyer 1977: 267, 1987:133–39; Patricia Kitcher 2011: 147). The appropriate feature isa type of unity or ordering of these states. The idea is that if therepresentations I can attribute to myself possess a unity of the rightkind, and if I apprehend or am cognitively sensitive to this unity,then I will be able to represent the apperceiving subject of any oneof them as identical with that of any other.

Thus my representation of the identity of the subject comes about“only in so far as I conjoin one representation with another,and am conscious of the synthesis of them” (B133). Thisconsciousness is profitably interpreted as conscious awareness not ofthe act or process of synthesis itself, but rather of the unity thatis its outcome (Strawson 1966: 94–6; Dicker 2004: 133–4)).What sort of unity must I consciously recognize among myrepresentations that would account for my representation of thisidentity? Note that it is not plausibly co-consciousness, for Irepresent the subject as identical for self-attributed representationsthat are not co-conscious, so actual co-consciousness could notexplain generally how I represent this sort of identity. A crediblealternative is that the unity consists in certain intimate ways inwhich representations in a single subject are typically related.Arguably, the essential feature of this unity is that a singlesubject’s representations be inferentially and causallyintegrated to a high degree, and in this respect they are unified in away in which representations possessed by discrete subjects are not.Alternatively, several commentators have argued that the relevantunity might be a temporal order among my representations, therebylinking the B-Deduction with the arguments of the Second Analogy andthe Refutation of Idealism (Guyer 1977: 267; Dicker 2004:137–44). A concern about this route is that a cognitivesensitivity to the time-ordering of representations does not obviouslyfacilitate our representing them as belonging to a single subject(Brueckner 1984: 199–208). By contrast, when mental states failto exhibit inferential and causal integration, as in the case ofmultiple-personality disorder, we have a tendency to posit multiplesubjects, while we do not do so when such integration is present.

In Kant’s view, the candidates for explaining how this kind ofunity comes to be, or, less ambitiously, for explaining my ability torecognize this sort of unity, are association and synthesis. At thispoint he appears to suppose that because Hume’s psychologicaltheory has already been ruled out, synthesis is the only remainingoption. So for me to represent the identity of the subject ofdifferent self-attributions, I must generate or at least recognize theright sort of unity among these representations, and synthesis must beinvoked to account for this unity. Thus Kant contends that thiscombination “is an affair of the understanding alone, whichitself is nothing but the faculty of combiningapriori” (B134–5. Since the understanding providesconcepts for synthesis, and because for synthesis to beapriori is, at least in part, for it to employa prioriconcepts, Kant is contending here that synthesis by means ofapriori concepts is required to account for the unity inquestion.

Here is an austere representation of the structure of the argument sofar:

1. I am conscious of the identity of myself as the subject ofdifferent self-attributions of mental states. (premise)
2. I am not directly conscious of the identity of this subject ofdifferent self-attributions of mental states. (premise)
3. If (1) and (2) are true, then this consciousness of identity isaccounted for indirectly by my consciousness of a particular kind ofunity of my mental states. (premise)
4. This consciousness of identity is accounted for indirectly by myconsciousness of a particular kind of unity of my mental states. (1,2, 3)
5. If (4) is true, then my mental states indeed have this particularkind of unity. (premise)
6. This particular kind of unity of my mental states cannot beaccounted for by association. (5, premise)
7. If (6) is true, then this particular kind of unity of my mentalstates is accounted for by synthesis bya priori concepts.(premise)
8. This particular kind of unity of my mental states is accounted forby synthesis bya priori concepts. (6, 7)

Premise (1) is intended as a claim the skeptic about the legitimateapplicability ofa priori concepts will at least initiallyaccept. The crucial necessary conditions, expressed by (3) and (7),are necessary conditions of only possible explanation. However, PaulGuyer forcefully argues that establishing the need for synthesis bymeans ofa priori concepts would require ruling out thealternative explanation that empirical information and conceptsderived from it is sufficient to account for the recognition of theunity at issue (Guyer 1987:146–7). And in his view it remainsopen, given what Kant has shown, that this recognition requires onlyawareness of information derived from inner sense or introspectiveexperience. Kant does not attempt at this point in the argument torule out such a rival empiricist hypothesis, but he arguably wouldneed to do so to establish the need fora priori synthesis.To advance his claims, one might appeal to features of this unity thatwould render such an empiricist account inadequate. As we shall see,Kant employs this tactic in the next phase of the argument, whichintroduces his account of our representations of objects.

1.2 Representations of Objects and the Single-Substantive-Premise Interpretation of the B-Deduction

According to one widespread reading of the B-Deduction,§§15–20 comprise a an argument whose only assumptionis the premise about self-consciousness that Kant defends in §16.Strawson, for example, is a proponent of such an interpretation(1966), as are Robert Paul Wolff (1963), Jonathan Bennett (1966),Henry Allison (1983), Edwin McCann (1985), and Dennis Schulting(2012a). Demonstrating that we represent objects or an objective worldhas a key role in most versions of this reading. On Strawson’sinterpretation, for instance, “the fact that my experience is ofa unified objective world is a necessary consequence of the fact thatonly under this condition could I be conscious of my diverseexperiences as one and all my own” (1966: 94). Some interpretersdissent; Karl Ameriks, for example, contends that Strawson’sconception of the Deduction is motivated by a desire to see it asshowing that the skeptic about the external world is mistaken, whilein fact refuting this sort of skeptic is not one of Kant’s aimsfor this argument (Ameriks 1978; also Allais 2011, 2015). PatriciaKitcher (2011: 115–18) argues against the single premise aboutself-consciousness interpretation on historical and textualgrounds.

An uncontroversial role of §17 is to provide a characterizationof an object, or more to the point, of a representation of an object,that facilitates a challenge to Humean associationism. Kant’sproposal is that an object is “that in the concept of which amanifold of a given intuition is united” (B137). Here‘object’ should be read in the broad sense ofobjective feature of reality – a feature whoseexistence and nature is independent of how it is perceived (B 142;Bird 1962/1973 130–31; Strawson 1966: 98–104; Guyer 1987:11–24). Allison is a proponent of the view that §17 containnot only this challenge to Hume, but also an attempt to demonstratethat we represent objects on the basis of the conclusions aboutself-consciousness established in §16. This interpretation is acomponent of Allison’s broader vision of the B-Deduction,according to which Kant demonstrates that the unity of apperceptionentails that we represent objects, and, conversely, that ourrepresenting objects entails the necessary unity of apperception(Allison 1983: 144ff; 2015: 352–55; 2015: 335–55, esp. 352)Indeed, the crucial claim for Allison’s interpretation is thatthe unity of apperception is not only a necessary but also sufficientcondition for our representing of objects. This he calls thereciprocity thesis. Other commentators, including RichardAquila (1989: 159), Howell (1992: 227–8) and Schulting (2012a)agree that the B-Deduction features the reciprocity thesis and anattempt to establish its truth, while Ameriks (1978) disagrees. On anaccount of the sort Ameriks favors, the unity of apperception, andmore exactly, the synthesis that explains our consciousness of theidentity of the subject, is only a necessary condition for therepresentation of objects (cf. Allais 2011).

Allison’s interpretation is attractive particularly because itpromises leverage against the skeptic who denies that we representobjects, and also because this leverage is generated by premises aboutself-consciousness that this skeptic is likely to accept.Nevertheless, there are textual and charitable reasons to resist thisreading (Ameriks 1978, Pereboom 1995; Patricia Kitcher 2011:115–60; Vinci 2014: 193–94). First of all, in§§18–20 Kant makes significant assumptions aboutfeatures of our representations of objects that exceed anything thathe has argued for in §17 or earlier. In particular, §18 heassumes that our representations of objects manifest a certain kind ofnecessity and universality, and this he does not purport to establishin §17 or earlier. Moreover, in the summary of the precedingsteps of the B-Deduction in §20 Kant does not include premisesfrom §§15–16. What we actually encounter in §20indicates that Kant intends §§17–20, with some helpfrom §13, to constitute a single, self-contained argument thatdoes not depend on the conclusions about self-consciousness developedin §§15–16.

On Allison’s conception, the argument from the unity ofapperception (or, equivalently, from the unity of consciousness) forour representing objects occurs in the following passage:

(A) Understanding is, to use general terms, the faculty of cognitions(Erkenntnisse). They consist (bestehen) in thedeterminate relation of given representations to an object: and anobject is that in the concept of which the manifold of a givenintuition is united. Now all unification of representations demandsunity of consciousness in the synthesis of them. Consequently it isthe unity of consciousness that alone constitutes the relation ofrepresentations to an object, and therefore their objective validityand the fact that they are cognitions (Erkenntnisse): andupon it therefore rests the very possibility of the understanding.(B137)

Allison himself presents a problem for his interpretation of thispassage. He contends, first of all, that the reciprocity thesis isencapsulated in this sentence:

1. It is the unity of consciousness that alone constitutes[ausmacht] the relation of representations to an object, andtherefore their objective validity.

and that Kant presents (1) as a direct consequence of the premisethat

2. all unification of representations demands unity of consciousnessin the synthesis of them.

Allison points out that on this reading Kant’s reasoning appearsto involve anon sequitur, since (2) supports onlyKant’s having in mind that the unity of consciousness is anecessary condition for the representation of an object, and not forits also being a sufficient condition. Howell raises a similarconcern: “In §17 Kant simply does not make this inferenceclear, and an air of blatant fallacy hovers over this part of hisreasoning” (Howell 1992: 228; for an opposing view see Keller1998: 80). But Ameriks argues that the B-Deduction should not beinterpreted as providing an argument for the sufficiency claim, and arespectable case can be made for his reading (Ameriks 1978; Pereboom1995; Patricia Kitcher 2011: 115–60).

Allison and Howell both argue that (1) should be read as a statementof the sufficiency claim. Now in (A) Kant contends that cognitions ofobjects consist in a determinate relation of representations toobjects, and as (1) indicates, this relation is constituted orproduced by a synthesis that essentially involves the unity ofconsciousness. However, (1) does not indicate that the synthesis thatinvolves unity of consciousness cannot occur without its resulting ina relation of a representation to an object. By analogy, the smeltingand molding of steel are processes that constitute or produce steelgirders, but from this one should not conclude that the processes ofsmelting and molding steel cannot take place without the production ofsteel girders. Just as producing steel girders also requires molds ofparticular shapes, so producing representations of objects mightrequire, in addition to the synthesis that involves the unity ofconsciousness, particular concepts of objects.

If the sufficiency claim, and with it the reciprocity thesis, isdenied, we need an alternative account of how §17 functions inthe overall argument of the B-Deduction. It may be that the role ofthis section is largely to provide a characterization of an objectthat has a key role in the ensuing challenge to Humean associationism,and thereby initiates an argument from below. Kant’s proposal isthat an object is “that in the concept of which a manifold of agiven intuition is united” (B137). The subsequent claim is thatthe unification of a manifold requires synthesis; immediatelyfollowing the characterization of an object he states that “allunification of representations demands unity of consciousness in thesynthesis of them” (B137). It seems consistent with these textsthat Kant’s characterization of an object is designed just topresent his anti-Humean theory of the mental processing required forrepresenting objects, and that the subsequent claim for the need forsynthesis does not express a view he expects us to accept withoutfurther argument, but rather one he aims to confirm in§§18–20. If this argument succeeds, it will turn outthat thea priori synthesis required to account for thefeatures of our representations of objects Kant singles out is thesame process that yields my consciousness of the identity of myself assubject of different self-attributions.

1.3 Universality and Necessity in our Experience of Objects

In §18 Kant draws our attention to certain features of ourrepresentations of objects that, in his view, will serve to defeatassociationism and establisha priori synthesis:

The transcendental unity of apperception is that unity through whichall the manifold given in an intuition is united in a concept of theobject. It is therefore entitled objective, and must be distinguishedfrom the subjective unity of consciousness… Whether I canbecomeempirically conscious of the manifold as simultaneousor as successive depends on circumstances and empirical conditions.Therefore, the empirical unity of consciousness, through associationof representations, itself concerns an appearance, and is whollycontingent… Only the original unity is objectively valid: theempirical unity of apperception,… which… is merelyderived from the former under given conditionsin concreto,has only subjective validity. One person connects the representationof a certain word with one thing, the other [person] with anotherthing; the unity of consciousness in that which is empirical is not,as regards what is given, necessarily and universally valid.(B139–40)

For Kant, a defining feature of our representations of objects istheir objective validity. For a representation to be objectively validit must be a representation of an objective feature of reality, thatis, a feature whose existence and nature is independent of how it isperceived (Guyer 1987:11–24). In this argument, it appears thatKant just assumes that the representations that make up experience areobjectively valid. He then aims to establish that association isinadequate because it can yield only representations that are notobjectively valid. In the above passage, Kant contends that ourobjectively valid representations must in a sense be necessary anduniversal. However, the empirical unity of consciousness, whichinvolves an ordering of representations achieved by association, canonly be non-universal, contingent, and hence merely subjectivelyvalid, by contrast with the transcendental unity of apperception,which involves an ordering that is universal and necessary, and istherefore objectively valid. In Kant’s conception, it is thefact that the transcendental unity of apperception is generated bya priori synthesis that allows it to yield an ordering thatis universal, necessary, and objectively valid. (Ameriks 1978,Pereboom 1995, Patricia Kitcher 2011: 115–60; Allais 2011, 2015;Vinci 2014). On Lucy Allais’s proposal, empirically we areacquainted with objects, but absent a priori synthesis, empiricalrepresentations would be of objects that are indeterminate withrespect to multiple possible ways of conceptualizing and individuatingthem. Only with a priori synthesis is the representation ofdeterminate objects possible. The concept of cause has a key rolehere, since determinacy is paradigmatically a function of representedcausal unity of objects (Allais 2015: 275–85; cf. Beck 1978;Vinci 2014: 134–44). This determinacy, by virtue of a sharedscheme of a priori concepts, yields the universality and necessityKant has in mind.

To illustrate and support these claims, Kant invokes examples of theordering of phenomena in time that also have the key role in thediscussion of the Second Analogy (cf. Guyer 1987: 87–90; Dicker2004: 137–44). There Kant argues that our representations,considered independently of their content, are always successive. Forexample, when I view the front, sides, and back of the house whenwalking around it, and when I watch a boat float downstream, myrepresentations of the individual parts and states occur successively.The content of these successive representations, however, can berepresented as either determinately and objectively successive or asdeterminately and objectively simultaneous. And as it in fact turnsout, despite the representations in each of these sequences beingsubjectively successive, we represent the parts of the house asobjectively simultaneous, and the positions of the boat as objectivelysuccessive. How might we account for this difference in objectivitydespite the similarity in subjectivity? (Melnick 1973: 89)

The important clue for answering this question is that theserepresentations of objective simultaneity and succession are universaland necessary. It is the universality and necessity of ourrepresenting the parts of the house as simultaneous that accounts forour representing them as objectively simultaneous, and theuniversality and necessity of our representing the positions of theboat as successive that accounts for our representing them asobjectively successive. Association is inadequate for accounting forthis objectivity because it is incapable of yielding such universalityand necessity, a defect not shared by synthesis.

A first approximation of the import of ‘universal’ in thehouse example is:

(U) Any human experience of the parts of the house is an experience ofthese parts as objectively simultaneous.

The addition of necessity has the following effect on (U):

(U-N, first pass) Necessarily, any human experience of the parts ofthe house is an experience of these parts as objectively simultaneous.

This claim would be resisted by Hume if the necessity were specifiedas ranging over all possible circumstances, for Hume’s theorywould allow for the possibility of a deviant ordering in unusualempirical conditions. But (U-N, first pass) can be reformulated moreprecisely as

(U-N) Necessarily, if empirical conditions are normal, any humanexperience of the parts of the house is an experience of these partsas objectively simultaneous.

Kant’s view is that given only the resources of association, thetruth of (U-N) cannot be explained. The reason is “whether I canbecome empirically conscious of the manifold as simultaneous or assuccessive depends on circumstances or empirical conditions,”and so “the empirical unity of consciousness, throughassociation of representations, itself concerns an appearance, and iswholly contingent” (B139–40). Association cannot explainthe truth of (U-N), for given only the resources of association, theparts of the house will not necessarily or universally be representedas objectively simultaneous even supposing only normal empiricalconditions. Kant asks us to consider an activity, word association,which functions as a paradigm for association. Word association,familiarly, does not yield universal and necessary patterns;“one person connects the representation of a certain word withone thing, the other [person] with another thing…”(B140). Hume’s own paradigm for association in is the relationsamong parts of a conversation (1748: §3). In such conversations,people make different associations in the same circumstances.Kant’s point is that if the very paradigms for association failto exhibit the sort of necessity and universality at issue, then thehypothesis that association is powerful enough to yield such anordering of representations – wherever we find it – isruled out. (Pereboom 1995; Dickerson 2004: 170–77; for anaccount of a more general relationship in Kant between universalityand necessity on the one hand and apriority on the other, see Smit2009).

Here we should see Kant as advancing his claim for the applicabilityof the categories by ruling out association as an explanation for(U-N). The structure of this (part of the) argument can be representedas follows:

9. We have representations of objects, i.e., of objectively validphenomena. (premise)
10. All of our representations of objects are (in part) of universaland necessary features of experience. (9, premise)
11. Necessary and universal features of experience cannot be explainedby association. (premise, from reflection on the nature ofassociation))
12. If (10) and (11) are true, all of our representations of objectsrequire a faculty for ordering mental states distinct fromassociation. (premise)
13. All of our representations of objects require a faculty forordering mental states distinct from association. (11, 12)
14. If (13) is true, all of our representations of objects require afaculty for synthesis bya priori concepts. (premise)
15. All of our representations of objects require a faculty forsynthesis bya priori concepts. (13, 14)

We can expand (15) to explicitly note the link to the argument fromabove:

To this we can add the final moves, which are explained in thesubsequent sections of the B-Deduction:

16. Insofar as our representations of objects require a faculty forsynthesis bya priori concepts, certaina prioriconcepts – the categories – legitimately apply to theseobjects. (premise)

3. We have representations of objects, and they are all such that thecategories legitimately apply to these objects. (9, 15, 16)

The key necessary conditions, expressed by (12) and (14), like thoseof the argument from above, are necessary conditions of only possibleexplanation.

Guyer objects that at various places in the Transcendental DeductionKant illegitimately assumes knowledge of necessity, and perhaps thisargument falls to such a concern (Guyer 1987: 146–7). While thisconcern has the potential of weakening Kant’s argument, perhapsHume would not deny the necessity under consideration at this point inthe argument. Hume does maintain that it is in some sense impossible,given an experience of constant conjunction, that the mind not becarried from an impression of the first conjunct to an idea of thenext:

… having found, in many instances, that any two kinds ofobjects, flame and heat, snow and cold, have always been conjoinedtogether; if flame or snow be presented anew to the senses, the mindis carried by custom to expect heat or cold, and tobelieve,that such a quality does exist, and will discover itself upon a nearerapproach. This belief is the necessary result of placing the mind insuch circumstances. It is an operation of the soul, when we are sosituated, as unavoidable as to feel the passion of love, when wereceive benefits; or hatred, when we meet with injuries. (1748:§5)

Thus Hume himself contends that given certain specific empiricalcircumstances, a particular type of ordering of perceptions in a sensenecessarily comes about.

A further concern of Guyer’s is that Kant assumes withoutdefense that all knowledge of necessity is grounded inapriori concepts. But, in response, perhaps we need not interpretKant as arguing directly from (U-N) to the claim that the categoriescorrectly apply to objects in our experience. Rather, we might see himas advancing his claim for the applicability of the categories byruling out association as an explanation for (U-N). This transitioncan be divided into three steps:

1. To explain the truth of (U-N), we must have a mental faculty otherthan association for ordering representations.
2. This faculty does not consist solely of sensory items.
3. This faculty must employa priori concepts, thecategories in particular.

The challenge Kant issues is to explain why, under normal conditions,the ordering in question is universal and necessary. Part of the bestexplanation, he believes, is (a), that we must have a faculty forordering the representations. Hume might agree with this conclusion,supposing a sufficiently thin conception of ‘faculty’. Yethe would deny (b), that this faculty does not consist solely ofsensory items. Kant argues that the Humean proposal for a faculty thatconsists solely of sensory items, the faculty of association, cannotaccount for the truth of propositions such as (U-N), for the veryparadigms of association, such as word association, and theassociation of topics in a conversation, do not exhibit the requisiteuniversality and necessity. The alternative that can account for thetruth of propositions such as (U-N) involves affirming (c), that thefaculty in question must be one that employs the categories.

The associationist might counter that sensory experience issufficiently uniform for association to produce the universalities andnecessities at issue. Perhaps Kant is too quick to conclude that theargument from universality and necessity is decisive, for in addition,associationist objections of this sort must be answered – ascontemporary critical discussions of proposals for innate conceptsindicate (Pereboom 1995: 31–3). But this does not detract fromthe anti-associationist force provided by the sorts of universalitiesand necessities Kant has in mind, and this fact is recognized by thecontemporary discussion.

1.4 Logical Forms of Judgment and the Categories

In §§19–20, Kant contends that the vehicle that bringsabout the synthesis at issue is judgment, and that this vehicleemploys certain forms of judgment, which are in turn intimatelyrelated to the twelve categories. By connecting synthesis to judgmentin this way, and the forms of judgment to the categories, Kant aims toshow that we must employ the categories in the synthesis of ourexperience of objects.

In §19, Kant argues that there must be a certain way in whicheach of my representations is unified in the subject, and heidentifies this way with judgment: “I find that a judgment isnothing but the manner in which given cognitions are brought to theobjective unity of apperception” (B141). Judgment, Kantproposes, is objectively rather than subjectively valid, and henceexhibits the type of universality and necessity that characterizesobjective validity (B142). He then claims that without synthesis andjudgment as its vehicle, an ordering of representations might reflectwhat appears to be the case, but it would not explain how we makedistinctions between objective valid phenomena (i.e., objects) and thesubjective states they induce (e.g, Allison 2015: 363–69; Sethi2020).

In §20, Kant ties this notion of judgment to the twelve forms ofjudgment presented in the Metaphysical Deduction (A70/B95), and hethen connects these forms of judgment to the twelve categories(A76–83/B102–9). The claim has often been made that thelinks Kant specifies between synthesis and judgment, judgment and theforms of judgment, the forms of judgment and the categories are notsufficiently supported. Guyer, for example, argues that Kant has notadequately established the last of these connections, that althoughKant claims that the categories are simply the forms of judgment asthey are employed in the synthesis of representations in an intuition(A79/B104–A80/B105, B143), he has failed to make this claimplausible (Guyer 1987: 94–102). It is fair to say that theseconcerns have merit. Kant’s assertions about these ties remainmore obscure than the preceding part of the Transcendental Deduction,and it continues to be a serious challenge for interpreters to clarifyand vindicate them.

Béatrice Longuenesse (1998), in her interpretation of theMetaphysical Deduction, takes up this challenge. In her view, thefaculty at issue in the production and use of concepts, theunderstanding, is the power to judge (Vermögen zuUrteilen), which is ultimately a disposition or aconatus to make judgments and to shape how we are affected sothat we can make them (Longuenesse 1998: 208, 394). The logical formsof judgment are in essence the forms of combination of concepts injudgments. One such form is the categorical, which is the form ofsubject-predicate judgments; another is the hypothetical, the form ofconditional judgments. Kant contends that the logical form of ajudgment is what makes it capable of truth or falsity, for by means ofsuch a form a judgment can constitute a relation of a subject’srepresentations to an objective feature of reality (Longuenesse 2000,93–4). For instance, by its categorical form, the judgment‘the boat is moving’ can constitute the relation of myrepresentations of a boat and of motion to an objectively existingboat in motion, and as a result this judgment can be true orfalse.

One role of the logical forms of judgment is in the process ofanalysis, by which the objects we intuit are subsumed under concepts.What results from this process is a judgment that expresses what Kantcalls ananalytic unity – paradigmatically, the unityin the subsumption of several intuited objects under a single concept.But a logical form of judgment can also function in a different role:in the synthesis of a manifold of an intuition. The result in thiscase is asynthetic unity, the unity of a synthesizedmultiplicity of representations in a single intuition. Theunderstanding, as the power to judge, functions in each of these tworoles; “the same function that gives unity to concepts injudgment, also gives unity to the mere synthesis of representations inintuition” (A79/B104–5). In its synthetic role, theunderstanding adds content to the forms of judgment:

The same understanding, and indeed by means of the very same actionsthrough which it brings the logical form of judgment into concepts bymeans of the analytical unity, also brings a transcendental contentinto its representations by means of the synthetic unity of themanifold in intuition in general. (A79/B105)

The addition of such transcendental content turns the form of judgmentinto a category. This content is a feature of the forms of intuition,space and time, which are called upon when the power to judge sets outto unify a manifold of intuition (B128–9). The categories– more precisely, the versions of the categories that areschematized for our way of cognizing (A137/B176ff) – are thusgenerated from the forms of judgment in the process of synthesizingintuitions by the addition of spatial and temporal content. Forexample, generated from the categorical form of judgment by theaddition of such content is the category of substance, and generatedfrom the hypothetical form of judgment in this way is the category ofcause. (For beings possessing the power of understanding but withdifferent forms of intuition, the categories would be schematizeddifferently from ours.)

1.5 The Second Step of the B-Deduction

In §20 Kant, draws a conclusion from the considerations he has sofar advanced: “Consequently, the manifold in a given intuitionis necessarily subject to the categories” (B143). One mightthink that this is precisely what Kant intended to establish in theTranscendental Deduction, and thus that the argument is brought to anend in §20. However, in §21 he indicates that theTranscendental Deduction is not yet complete: “Thus in the aboveproposition a beginning is made of a deduction of the pure concepts ofunderstanding” (B144). Kant goes on to explain:

In what follows (cf. §26) it will be shown, from the mode inwhich the empirical intuition is given in sensibility, that its unityis no other than that which the category (according to §20)prescribes to the manifold of a given intuition in general. Only thus,by demonstration of thea priori validity of the categoriesin respect of all objects of our senses, will the purpose of thededuction by fully attained. (B144–5)

Here a perennial interpretive question arises: how should we construethe argument we find in §26, together with material from§24, which is sometimes designated as the second step of theB-Deduction?

One position on this interpretive issue is advanced by Erich Adickes(1889: 139–4) and H. G. Paton (1936, v. 1: 501), who argue thatwhile the material that precedes §21 constitutes anobjective deduction, material in §24 and §26comprise asubjective deduction. This distinction has itssource in the Preface to the A edition:

This enquiry, which is somewhat deeply grounded, has two sides. Theone refers to the objects of pure understanding, and is intended toexpound and render intelligible the objective validity of itsapriori concepts. It is therefore essential to my purposes. Theother seeks to investigate the pure understanding itself, itspossibility and the cognitive faculties upon which it rests: and sodeals with it in its subjective aspect. Although this latterexposition is of great importance for my chief purpose, it does notform an essential part of it. (Axvi–xvii)

Henrich (1968–69) rejects the Adickes/Paton proposal for thereason that in §21 Kant states that the demonstration of thevalidity of the categories is completed only in §26, and thepassage from the A-Preface indicates that this is a task for theobjective deduction. In defense of Adickes and Paton, in §20 Kantclaims to have established that the categories apply to the manifoldin any one given intuition, and affirms that he will now show thatcategories apply to any object presented to the senses. In view of theaim of the objective deduction, this move would seem to require only astraightforward and trivial application of the result of §20 toany empirical intuition we might have (as many commentators havenoted). So, on a charitable interpretation of Kant’s agenda,showing that the categories apply to any object presented to thesenses plausibly involves considerations beyond the scope of theobjective deduction.

Henrich points out that although in the B-Deduction Kant sought toavoid the problems of a subjective deduction, this “does notmean that he neglected the demand for an explanation of thepossibility of relating the categories to intuitions.” However,by Kant’s account, a subjective deduction features not only anexamination of cognitive faculties, but also an investigation of“the possibility of the pure understanding,” which wouldinclude an investigation of how the categories are related to a prioriand to empirical intuition and to the objects presented to us in suchintuition. This is precisely the type of inquiry that we encounter in§24 and §26 – and Henrich agrees. Thus it seems thatthe views of Henrich, Paton, and Adickes can be reconciled: theyconcur that the second step aims to show how it is that the categoriesare related to objects of intuition and thus of experience in such away as to demonstrate that they correctly apply to them.

Anil Gomes (2010) proposes a more precise hypothesis for what ismissing in the first step that is addressed by the second step. Gomesfirst appeals to a problem James van Cleve (1999) raises for theTranscendental Deduction. Even if Kant succeeds in showing thatsynthesis involves judging, and that judging involves the applicationof the categories.

this would not be enough for his purposes. For that result inconjunction with the rest of the Transcendental Deduction would yieldno conclusion stronger than this: all my representations are connectedin judgements that use Kant’s categories. But Kant wants to showthat the categories are objectively valid – that they actuallyapply to objects of experience. (van Cleve 1999: 89)

Kant hasn’t established, according to van Cleve, that thecategories actually apply to experience. As Gomes (2010: 121) puts it,“perhaps our application of the categories in experience isalways mistaken, and there is nothing which corresponds to the way inwhich we have synthesized the manifold.” As he points out, thesecond step reaches its conclusion through the analysis of thestructure of our representation of space and time, from which Kantthen draws the conclusion that space and time themselves feature thatstructure (Gomes 2010: 130; he cites a similar claim by Longuenesse1998, 213). If space and time do feature the structure of ourrepresentations of them, then the requisite correspondence is inplace, and van Cleve’s objection is answered.

This is a contending and plausible hypothesis for a role for thesecond step in the B-Deduction. One might ask, however, whether theaccount Kant provides can respond convincingly to van Cleve’sobjection. Even on certain idealist views, such as Leibniz’s andKant’s according to Robert Adams (1983, 1994: 217–61, cf. Wilson1987), our ordinary sensible representations of space, and of physicalentities more generally, may not represent them as they really are. Bycontrast, on Berkeley’s idealist position as represented in thethird of theThree Dialogues between Hylas and Philonous(Berkeley 1713/1998), the properties of physical entities match oursensible representations of them exactly, without a possibility of amismatch; the oar in the water really is bent when I see it as bent.On the type of idealism Kant endorses (and one might of coursequestion whether it has been established), the possibility of amismatch remains in place even if our representation of spacestructures space itself (Pereboom 1988; Stang 2018; Jauernig 2021).For instance, we may sensibly represent space as Euclidean while is infact Riemannian. One might respond that the representation thatstructures space would then also be Riemannian, and we would have amatch. But then a crucial feature of our representation of space wouldbe inaccessible absent serious empirical investigation, and the natureof the project would be altered.

The core text that divides interpretations of the second step is thenote to B160–1:

Space, represented as object (as is really required in geometry),contains more than the mere form of intuition, namely thecomprehension of the manifold given in accordance with the form ofsensibility in an intuitive representation, so that the form ofintuition merely gives the manifold, but the formal intuition givesthe unity of the representation. In the Aesthetic I ascribed thisunity merely to sensibility, only in order to note that it precedesall concepts, though to be sure it presupposes a synthesis, which doesnot belong to the senses but through which all concepts of space andtime first become possible. For since through it (as the understandingdetermines the sensibility) space or time are first given asintuitions, the unity of this a priori intuition belongs to space andtime, and not to the concepts of the understanding (§24).

It’s widely agreed that a crucial feature of the second step isthe claim that our intuitions of space and time are constituted insuch a way as to necessitate the unification of the manifold ofappearance by the application of the categories. In the TranscendentalAesthetic, Kant aimed to show that space and time are forms of oursensible intuition, and that for us appearances can only occur inaccord with these forms. But now, in the note to B160–1, Kant drawsour attention to the fact that space and time are not only forms ofintuition, but are intuitions themselves, and that they are intuitionsthat feature unity. What’s more, Kant specifies that this unity‘precedes all concepts, though to be sure it presupposes asynthesis, which does not belong to the senses but through which allconcepts of space and time first become possible.’ By thesynthesis that is presupposed ‘the understanding determines thesensibility.’ So the unity of space and time is to be explainedwith reference to the effect of the understanding upon sensibilityitself (Longuenesse 1998: 211–33; Keller 1998: 88–94;Dickerson 2004: 196–201; Pollok 2008; Vinci 2014: 197–229;Onof and Schulting 2015; Allison 2015: 374–432; Rosefeldt 2022).

The text, and in particular the B160–1 note, gives rise to a number ofinterpretive issues for Kant’s overall position. One is whetherhere Kant countenances a kind of unity in our representations that isnot a result of categorical synthesis, but is instead is independentof the categories. Hermann Cohen (1871/1987, 1907) and Eric Dufour(2003) are strict categorical conceptualists about any such unity,while Martin Heidegger (1929/1997) argues that there is a unity thatis accounted for by the productive imagination independently of thecategories; (Lorne Falkenstein 1995, Michel Fichant 1997, Robert Hanna2008, 2011, Stephanie Grüne 2011, Dennis Schulting 2012b, JamesMessina 2014, Colin McLear 2015, and Jessica Wilson 2018 also defendnonconceptualist positions on this score; see McLear 2014, 2020 foroverviews). Longuenesse (1998) contends that unity-yielding synthesisis always a function of the understanding, but that there is a kind ofsynthesis of the understanding that does not involve the categories,while it yet anticipates them. Messina (2014), McLear (2015), Onof andSchulting (2015), and Wilson (2018) argue that there are multiplekinds of unity for Kant, and while some require categorical synthesis,others do not. In particular, they maintain that space as intuited byus has a unity that Onof and Schulting (2015) call unicity, whichconsists of its singularity, its infinity, and its mereologicalinversion, i.e., a metaphysical structure involving partsontologically depending on the whole, by contrast with the wholeontologically depending on parts, as is the case for material objectsgenerally (here see Desmond Hogan 2021). Intuitive awareness of spaceas featuring unicity does not, on their account, require categoricalsynthesis.

As Tobias Rosefeldt (2022) points out, a longstanding puzzle for theB160–1 note is that it references a notion of synthesis that precedesall concepts, while the notion of synthesis to which Kant appeals inthe preceding sections of the B-Deduction is one that does employconcepts, i.e., the categories, and thus does not precede concepts.Commentators generally agree that this synthesis that precedes allconcepts must be subject to the unity of apperception (e.g., Messina2014, Williams 2018), but how might it be more thoroughlycharacterized? Rosefeldt proposes an account of the second step thatat this point features the notion of a decomposing synthesis, whichcontrasts with a composing synthesis. Kant, as he points out,introduces the notion of a decomposing synthesis only in the SecondAntinomy (A505/B533, A524/B552), but in Rosefeldt’s view thisnotion is aptly suited for Kant’s objectives for the secondstep. While a compositional synthesis constructs a whole from givenparts,a decomposing synthesis begins with a given whole and thendecomposes it in some way into parts. In this context, it decomposesspace as we are intuitively aware of it into one or more of its finiteparts, such as spheres or cubes, while the remaining infinite spatialregion excluded by those parts is represented as their phenomenalbackground or horizon (cf., Husserl 1913, 1939).

A test for this proposal is how a decomposing synthesis mightrepresent space given that we conceptualize it as infinite. OnRosefeldt’s account, the decomposition into finite parts mayinvolve imaginatively drawing line segments that form a square. We cansubsequently extend these lines in the imagination, and we areconscious that we can freely vary the lines so that “howeverlarge the finite space that we construct by drawing lines is, thisspace will always only be phenomenally present to us within thehorizon of a still larger unlimited space.” This does not amountto intuiting space as infinite, but rather coming to understand thatthe space we intuit is infinite by aprogressus ad infinitum(A510–11/B538–39), a progression of a series that we understand isnever complete (Onof and Schulting 2015). Accordingly, space itself,in this way given as infinite, is an object of intuition for us as thephenomenal horizon of finite regions of space from which wedistinguish it in the decomposing synthesis. A parallel account holdsfor time. This account supplies the meaning, Rosefeldt argues, ofKant’s claim that “a synthesis which does not belong tothe senses” is required for “space and time [to be] firstgiven to us as intuitions” (B160–1n).

As Rosefeldt notes, the conclusion of the second step, theapplicability of the categories to space and time, requires appeal toa composing synthesis, since the decomposing synthesis precedes allconcepts, and only in the composing synthesis are the categoriesinvoked. Thus a transition from the decomposing to a composingsynthesis must be made. One possible strategy is to claim that acomposing synthesis is not required for our representation of space aswhole, but only for our representations of determinate parts of space,as when we construct figures in geometry. But while the text of theB160–1 note does reference geometry, it also suggests (in the finalsentence) that a composing synthesis is required for ourrepresentation of space as a whole. Onof and Schulting (2015) arguethat it is our explicit representation of the unicity of space as awhole that requires synthesis in accord with the categories, and theyembellish their account by specifying precisely which categories arerequired for the various aspects of unicity (Allison 2015: 420–30provides a complementary account). An alternative, suggested byRosefeldt (2022), is that first of all, the finite spatial parts thatwe actually distinguish in decomposing synthesis, either of individualspatial parts or of various such parts taken as a group, feature aunity, representation of which must be accounted for by compositionalsynthesis. But further, we are conscious of the fact that the infinitespace revealed as the phenomenal horizon in the decomposing synthesiscan be subdivided infinitely into finite spatial parts, all of whichare represented as parts of that one all-encompassing infinite space.Our representation of the unity of all of this, which Rosefeldt callsworld-unity, must also be accounted for by a composing synthesis. Fromthis we can see that given that a composing synthesis accounts for therepresented unity of the actual finite spaces we distinguish, it canaccount for the represented world-unity as well. (For a discussion onhow a composing synthesis can operate on a target that isindeterminate in the way that world-unity is, see Daniel Sutherland2021, ch. 5, referenced in Rosefeldt 2022: 16 n.5).

Since it has already been shown that composing syntheses generallymust feature the categories, the claim is that we can infer that thecategories structure our representation of space, and by parallelargument, our representation of time, and, moreover (in accord withKant’s idealism), that they structure space and time themselves,together with the spatial and temporal features of objects in spaceand time. This allows us to see that the categories correctly apply toobjects in space and time, and to see that they do so from how theystructure our representations of space and time, and space and timethemselves. This would secure the generally agreed-upon objective ofthe second step: to show how it is that the categories are related toobjects of intuition and thus of experience in such a way as todemonstrate that they correctly apply to them.

2. The Refutation of Idealism

In the transcendental argument of the Refutation of Idealism,Kant’s target is not Humean skepticism about the applicabilityofa priori concepts, but rather Cartesian skepticism aboutthe external world. This argument was added by Kant to the secondedition of theCritique of Pure Reason (B274–279, witha change suggested in the Preface to B, Bxxxix–Bxli), andsubsequently embellished and reworked in a series of Reflections(Guyer 1987: 279–316). More specifically, Kant intends to refutewhat he calls problematic idealism, according to which the existenceof objects outside us in space is “doubtful andindemonstrable” (B274). His strategy is to derive the claim thatsuch objects exist from my awareness that my representations have aspecific temporal order. At the present time I am aware of thespecific temporal order of many of my past experiences, an awarenessproduced by memory. But what is it about what I remember that allowsme to determine the temporal order of my experiences? There must besomething by reference to which I can correlate the rememberedexperiences that allows me to determine their temporal order. Butfirst, I have no conscious states that can play this role. Further,this reference cannot be time itself, for “time by itself is notperceived;” Kant argues for this claim in the First Analogy(B224–5). As Guyer puts it, it is not as if the content ofmemories of individual events are manifestly indexed to specifictimes, as sportscasts and videotapes often are (Guyer 1987: 244). Kantcontends that the only other candidate for this reference is somethingoutside of me in space, and it must be something (relatively)permanent (cf. First Analogy, B224–5). Perhaps this claim ismade plausible by how we often actually determine the times at whichour experiences occur. We use observations of sun’s positions,or of a clock that indicates time by way of the period of a pendulum,or by the period of the vibration of a cesium atom. Kant’sargument can be seen as exploiting this fact, together with theobservation that there is no similar periodic process in humanconscious experience considered independently of any spatial objectsit might represent, and that we lack any awareness of time by itself,to show we must perceive objects outside us in space by reference towhich we can determine the temporal order of our past experiences.

George Dicker provides a compelling initial representation ofKant’s argument (Dicker 2004, 2008):

1. I am conscious of my own existence in time; that is, I am aware,and can be aware, that I have experiences that occur in a specifictemporal order. (premise)
2. I can be aware of having experiences that occur in a specifictemporal order only if I perceive something permanent by reference towhich I can determine their temporal order. (premise)
3. No conscious state of my own can serve as the permanent entity byreference to which I can determine the temporal order of myexperiences. (premise)
4. Time itself cannot serve as this permanent entity by reference towhich I can determine the temporal order of my experiences.(premise)
5. If (2), (3), and (4), are true, then I can be aware of havingexperiences that occur in a specific temporal order only if I perceivepersisting objects in space outside me by reference to which I candetermine the temporal order of my experiences. (premise)
6. Therefore, I perceive persisting objects in space outside me byreference to which I can determine the temporal order of myexperiences. (1–5)

Several points of interpretation should be noted. First, it isgenerally agreed that the notion of awareness in Premise (1) should beinterpreted as a success notion, i.e., that to be aware that I haveexperiences that occur in a specific temporal order is to correctlydetermine that they occur in this order (Allison 1983: 290ff, Guyer1987: 293ff, Dicker 2004, 195ff., 2008; Chignell 2010). Second, mostcommentators concur that the experiences at issue are my pastexperiences. Guyer suggests that the argument might be extended tocombinations of my past and my present experience, but Dicker objectsthat the fact that past experiences occurred before the present one isdirectly knowable by introspection, and so doesn’t require theexternal reference (Guyer 1987; Dicker 2004: 195ff.). Third, JonathanBennett points out that we have single memories whose content spans anappreciable length of time that allow us to determine the order ofpast mental states . When one remembers hearing a certain word, onecan accurately determine by the content of a single memory thatcertain phoneme-experiences occurred prior to otherphoneme-experiences – for example, that one heard‘mad’ and not ‘dam’ (Bennett 1966:228–9). Dicker (2004: 201–2) remarks that we may be ableto determine accurately the order some of our past states by means ofsuch memories, but we cannot ascertain the order of most of our pastexperiences in this way. He therefore advocates a restriction of theargument to the experiences we can correctly order but not in the wayBennett adduces. Fourth, many commentators have noted that we mighthave perceived time directly. Guyer, as we just saw, suggests that allof our conscious experiences might have featured a time clock, muchlike a television sportscast or a video camera (1987: 244; cf.Strawson 1966). But as Dicker points out, in actual fact ourexperience does not have any such feature, and he is content forPremise (4), that time itself cannot serve as the reference whereby Icorrectly determine the temporal order of my past experiences, tostate a merely contingent fact about us (2004, 2008). Chignell (2010)expresses a concern about interpretations of the Refutation in whichit is merely a contingent fact about us that the alternative methodsfor determining the temporal order of my past experiences areunavailable, for then the conclusion, that we perceive objects inspace, would inherit such mere contingency, which he argues to be atodds with Kant’s hopes for the Refutation. Fifth, commentatorsdiffer on the relation that must obtain between the objects in spaceand the experiences whose temporal order we can correctly determine.Guyer argues that the relation must be causal, since “the statesof the self are judged to have a unique order just insofar as they arejudged to be caused… by the successive states of enduringobjects” (Guyer 1987: 309; cf. Dicker 2004: 200, 2008). Bycontrast, in Allison’s view we require the temporal order ofobjects in space only as a backdrop against which to determine thetemporal order of our experiences; “an enduring, perceivableobject (or objects) is required to provide a frame of reference bymeans of which the succession, coexistence, and duration ofappearances in a common time can be determined” (Allison 1983:201). If the object in space that provides the reference is the sun,for example, the states of the sun don’t need to cause myexperiences for me to determine their temporal order by means of thosestates.

Three of the most pressing problems that have been raised for theRefutation are the following. First, a skeptic might well rejectPremise (1) on the ground of a general skepticism about memory(Allison 1983: 306–7). Bertrand Russell, for example, suggeststhat for all I know I was born five minutes ago (Russell 1912). Onthis skeptical hypothesis, I would be mistaken in my belief that I hadexperiences A, B, and C which occurred more than five minutes ago,first A, then B, and lastly C. Plausibly, a skeptic who claimed thatwe lack adequate justification for a belief that external objectsexist would likely also be disposed to claim that I lack justificationfor my belief that I had experiences that occurred in the past in thatspecific temporal order. Thus Kant’s supposition that Premise(1) yields leverage against an external-world skeptic is mistaken (cf.Dicker 2008, Chignell 2010).

Second, consider the claim that my mental states (or the mentalsubject itself) are as suited as objects in space to function as areference whereby I can correctly judge the temporal order of my pastexperiences. Suppose I had available as such a reference only the meremental appearance of a digital clock in one corner of my field ofconsciousness. This would not clearly be less effective than an actualclock in space. To this one might reply, with Dicker, that there areno actual mental states that are adequate to serve as such areference. However, and this is the deeper worry, on Berkeley’sidealist view according to which theesse (to be) of objectsin space is theirpercipi (to be perceived), any spatialobjects would be nothing more than mental states of some subject, oraspects of those states, but Berkeleyan spatial perceptions would beas adequate a reference by which to determine the temporal order of mypast experiences as perceptions of spatial objects that are in somesense distinct from my mental states (cf. Allison 1983: 300–1;Vogel 1993; Chignell 2010).

Third, one might contend that Kant’s Refutation demonstratesthat the reference in question must be (relatively) permanent, andthat there is nothing in the Berkeleyan spatial realm that satisfiesthis requirement. However, to this one might respond that thereference by which I determine the temporal order of my pastexperiences need not be permanent in a way that cannot be satisfied byBerkeleyan spatial objects. If in the corner of my field ofconsciousness featured distinct momentary flashes, every second,indicating the date and time to the second, I would be able todetermine the temporal order of my past experiences by their means(cf., van Cleve, reported in Dicker 2004: 207).

A note on the second of these concerns: Several commentators haveargued that Kant’s Refutation of Idealism is meant to undermineany metaphysical sort of idealism, including metaphysical idealismsthat have been attributed to Kant (Guyer 1987: 317–29). Butwhile this reading has interesting support, one should hesitate toendorse it solely on the ground that Kant maintains that spatialobjects are distinct from the states of the perceiver. On a plausiblemetaphysical interpretation of Kant’s idealism, theesse of objects in space is not theirpercipi, sinceKant’s spatial objects, by contrast with Berkeley’s, arerecognition-transcendent. In Berkeley’s position, asubject’s perception of an oar in the water as crooked is not amisperception, for “what he immediately perceives by sight isnot in error, and so far he is in the right,” and it ismisleading only because it is apt to give rise to mistaken inferences(Berkeley 1713: Third Dialogue); while for Kant this perception is inerror. In Kant’s view, the oar is recognition-transcendent byvirtue of the Second Postulate’s provision that the actuality ofsuch objects is determined causally:

That which is bound up with the material conditions of experience,that is, with sensation, is actual (wirklich). (A218=B266)

The actual is that which conforms to the system of empirical causallaws (A225/B272ff.), and because the crookedness of the oar does notso conform, it is not actual. How the Second Postulate rules out theexistence of the apparent spatial objects of dreams and hallucinationsis spelled out in the third note to the Refutation of Idealism:

Note 3. From the fact that the existence of outer things is requiredfor the possibility of a determinate consciousness of the self, itdoes not follow that every intuitive representation of outer thingsinvolves the existence of those things, for their representation canvery well be the product merely of the imagination (as in dreams anddelusions). Such representation is merely the product of previousouter perceptions, which, as has been shown, are possible only throughthe reality of outer objects… Whether this or that supposedexperience be not purely imaginary, must be ascertained from itsspecial determinations, and through its congruence with the criteriaof all actual experience (wirklichen Erfahrung).(B278–9 cf.A376, cf. A492=B520–1)

The objects of dreams and hallucinations don’t meet thecriterion of actuality of the Second Postulate, that is, accordingwith the laws of causality. Thus while in Berkeley’s view theesse of spatial things consists in their being perceived bythe senses, for Kant they are the objects of the correctcausal/scientific account of the contents of our outer experience.This causal criterion allows that a spatial object, or, moreprecisely, the matter from which it is constituted, is (at leastrelatively) permanent – which would seem ruled out inBerkeley’s position, since the spatial object does not last anylonger than the idea does. (Berkeley does say that the ideas of what“are called real things” differ from “those excitedin the imagination” by “being less regular, vivid, andconstant” (Berkeley 1710,Principles Part I, 33), butfor him this difference does not challenge or undermine the claim thattheesse of a physical object is itspercipi.) Noneof this forces a metaphysical realist as opposed to an idealistreading of Kant.

Yet at the same time, according to the second concern, the Refutationis inadequate even if its ambition is restricted to demonstrating theexistence of merely metaphysically ideal but nonethelessrecognition-transcendent objects outside us in space. For grantingthat the Refutation establishes that for me to determine the temporalorder of my past experiences I must perceive objects in space, itfails to show that I need to perceive spatial objects any morerealistic than the Berkeleyan ones. More generally, the worry is thatBerkeleyan version of idealism has the resources to yield as adequatea reference for me to determine the temporal order of my pastexperiences as any rival position Kant is plausibly interpreted asendorsing, and that for this reason the Refutation falls short of itsaim.

3. Contemporary World-Directed Transcendental Arguments

Kant-inspired transcendental arguments against skepticism about theexternal world were developed with vigor in the mid-twentieth century,notably by P. F. Strawson, most famously in his Kantian reflections inThe Bounds of Sense (1966). These arguments are oftenreinterpretations of, or at least inspired by, Kant’sTranscendental Deduction and his Refutation of Idealism. Some are moreambitious than Kant’s would seem to be, insofar as they attemptto refute some variety of skepticism by showing that there is anessential commitment of the skeptical position for which the falsityof that position is a necessary condition (Nagel 1997: 60ff.).Strawson’s most famous transcendental argument (1966:97–104) is modeled on the Transcendental Deduction, butexplicitly without a commitment to synthesis or any other aspect ofKant’s transcendental psychology. His target is a purelysense-datum experience, which does not feature objects,“conceived of as distinct from any particular states ofawareness of them,” that is, a Berkeleyan experience of spatialobjects whoseesse ispercipi (1966: 98). The coreof the argument is as follows. From the premise that every (human)experience is such that it is possible for its subject to become awareof it and ascribe it to herself, we can infer that in every experiencethe subject must be capable of distinguishing a recognitionalcomponent not wholly absorbed by, and thus distinct from, the itemrecognized (1966: 100). From this we can infer that the subject mustconceptualize her experiences in such a way so as to contain the basisfor a distinction between a subjective component – how theexperienced item seems to the subject, and an objective component– how the item actually is. Strawson specifies that“collectively,” this comes to “the distinctionbetween the subjective order and arrangement of a series of suchexperiences on the one hand, and the objective order and arrangementof the items of which they are the experiences on the other”(1966: 101). Conceptualizing experience as involving an objectiveorder and arrangement of items amounts to making objectively validjudgments about it, which, in turn, implies that experience mustconsist of a rule-governed connectedness of representations (1966:98). Summarizing, from a premise about self-consciousness, we caninfer that the subject must conceptualize her experience so as tofeature a distinction between “the subjective route of hisexperience and the objective world through which it is a route,”where the experience of the objective world consists in arule-governed order of representations (1966: 105).

Barry Stroud, in his 1968 article “TranscendentalArguments,” issued a formidable challenge to the enterprise ofdefeating the external-world skeptic by transcendental arguments ofthis sort (Stroud 1968). There Stroud contends that suchtranscendental arguments are undermined by a problem which can bestated quite generally. These arguments feature reasoning from someaspect of experience or knowledge to the claim that the contestedfeature of the external world in fact exists. In each case theexistence of the external feature will not be a necessarycondition of the aspect of experience or knowledge in question, for abelief about the external feature would always suffice.Although the claim about existence of the aspect of the external worldcould be secured if certain kinds of verificationism or idealism werepresupposed, these views are highly controversial. Besides, one couldmake as much of an inroad against the skeptic armed with theverificationism or idealism alone, without adducing the transcendentalargument at all (cf. Brueckner 1983, 1984).

Although Strawson’s transcendental argument inThe Bounds ofSense is not a specific target in Stroud’s (1968), AnthonyBrueckner suggests that it is susceptible to the line of criticismthat Stroud develops (Brueckner 1983: 557–8). For, arguably,Strawson can only conclude that experience must be conceptualized in acertain way, such as to allow the subject to make the distinctionbetween an objective world and her subjective path through it. This isnot a conclusion about how a mind-independent world must be, but onlyabout how it must be thought. (Alternatively, Strawson might be readas drawing only a conclusion about how experience must beconceptualized, which would render the transcendental argument as oneof a more modest variety (see below)).

Recent developments of transcendental arguments reflect a struggle toaccommodate Stroud’s criticism, and often chastened expectationsabout what such arguments might establish by way of refutingskepticism. One more modest sort of transcendental argument beginswith a premise about experience or knowledge that is acceptable to theskeptic in question, and then proceeds not to the existence of someaspect of the external world, but in accord with Stroud’scriticism, to a belief in the existence of some aspect of the externalworld. Stroud himself advocates a strategy of this sort (Stroud 1994,1999), as does Robert Stern (1999). The kind proposed by Stroud beginswith the premise that we think of the world as being independent ofus, and it concludes, as a necessary condition of this premise, thatwe must think of it as containing enduring particulars. Such anargument does not claim that as a necessary condition of this premisethere must exist such particulars. It contends only for “aconnection solely within our thought: if we think in certain ways, wemust think in certain other ways” (Stroud 1999: 165). A belief orthought to which one reasons in this way would, in Stroud’sconception, have a certainindispensability, “becauseno belief that must be present in any conception or any set of beliefsabout an independent world could be abandoned consistently with ourconception of the world at all,” and it would beinvulnerable “in the special sense that it could not befound to be false consistently with its being found to be held bypeople” (Stroud 1999: 166).

Stern advances a conception of this kind of argument on which itaddresses a skeptic who questions whether certain beliefs cohere withothers in one’s set, as opposed to a skeptic who questionswhether certain beliefs are true (Stern 1999). A modest transcendentalargument would then aim to show that a belief whose coherence with theother beliefs is challenged so coheres after all. The requisitecoherence might be demonstrated by showing that the belief in questionis actually a necessary condition of a belief that is indispensable(in some coherentist sense) to one’s set. Mark Sacks (1999)objects that if at the same time one were to admit that the beliefmight not be true, one’s sense that one is justified in holdingthe belief would be undermined. This worry is a serious one. Sacksargues that it arises because of a tension between the coherentisttheory of justification and the realist correspondence theory of truththat the external world skeptic presupposes. One might respond, hepoints out, by accepting a coherence theory of truth as well, but thiswould be to adopt a version of idealism. Moreover, it seems thatSacks’s proposal would not solve the problem, for the reasonthat even if one accepted a coherence theory of truth, one would stillhave to admit that for specific instances of a belief one might bemistaken, even if one maintained that one was justified in holdingthat belief on grounds of coherence.

An important criticism of Stroud’s proposed sort of modesttranscendental argument is raised by Brueckner (1996). Brueckneraddresses the fit between the claim that certain non-skeptical beliefsare invulnerable in Stroud’s sense, and the admission that theymight not be true. More precisely, he challenges the claim that onecan simultaneously affirm the following two principles, each gleanedfrom Stroud (1994):

(CT) If we attribute beliefs to speakers (if we believe that they havebeliefs with determinate contents), then we must also believe thatthere is an independent world of enduring objects with which theyinteract.

and

(SK) Although we believe many things about a world independent of usand our experiences, … none of those beliefs is true.

Brueckner divides (SK) into

1. we believe many things about an external reality independent of usand our experiences

and

2. none of these beliefs is true.

Stroud argues, in effect, that given CT we cannot believe that (i) and(ii) are true, but nonetheless, we can believe that (i) and (ii) arelogically compossible given CT. Brueckner argues that using similarreasoning, given CT we cannot conceive of a possible world in whichboth (i) and (ii) hold, and this fact undermines Stroud’s claim.To conceive of a world W in which (i) is true is to conceive of aworld in which we (in the actual world) attribute beliefs aboutmind-independent objects to counterfactual versions of us (CVs) in W.But given CT, we must now also conceive of W as featuringmind-independent objects with which these CVs interact. Consider theCVs’ beliefthat there exist mind-independent objects– a belief they share with us. This belief of theirs will betrue. And thus in W (ii) will be false. Hence we have not conceived ofa world in which given CT, SK is nevertheless true, and indeed, wewill not be able to conceive of such a world. But our not being ableto conceive of a possible world in which given CT, SK is true,constitutes strong evidence against the claim that SK is logicallypossible given CT (1996: 274–75). Brueckner does not think thatthis argument demonstrates that it is inconsistent to accept CT andassert that SK is logically possible, but that there will be noevidence of the usual kind for this claim – evidence fromconceivability. Thus given the transcendental argument he advances,Stroud will be pushed in the direction of the immodest conclusion thatit is not possible for us to be mistaken in our belief that thereexist mind-independent objects.

From this one might be tempted to conclude that despite his critiqueof 1968, Stroud, with Brueckner’s assistance, has found atranscendental argument that does in fact establish a conclusion aboutthe external world. However, so far nothing has been said to turn backStroud’s 1968 critique, and it seems much more likely that theargument Stroud now advances can at best conclude with a version of CTin which the term “independent” must be read in atranscendentally ideal sense – in which, for example, the natureof certain physical objects is determined by our best scientifictheories about them, and our sensory experiences can be in error aboutthese objects. And if this is so, then the argument would secure abelief about the external world only on the presupposition ofmetaphysical idealism, and this is one of the ways in whichanti-skeptical transcendental arguments might be doomed according toStroud’s 1968 critique.

Despite these sorts of challenges, the aspiration to forgetranscendental arguments with considerable anti-skeptical force hasnot waned. Qassim Cassam (1999), Sacks (2000), and Stern (2000), forexample, have developed creative and nuanced versions oftranscendental arguments designed to negotiate the type of problemStroud has pressed.

4. Contemporary Practical Transcendental Arguments

Kant ethical writings (1785, 1788) feature several widely andintensely discussed transcendental arguments (see the entryKant’s moral philosophy). As in metaphysics and epistemology, in recent times anti-skepticaltranscendental arguments have also been developed in the practicalsphere.

One of P. F. Strawson’s most influential works is his essay onmoral responsibility, “Freedom and Resentment” (Strawson1962). The reasoning in this article has not traditionally beeninterpreted as a transcendental argument, but recently Justin Coateshas made a strong case for such a reading (Coates 2016; cf. Pereboom2016). In Coates’s account, the argument begins with the premiseto which the moral responsibility skeptic would agree, that meaningfuladult interpersonal relationships are possible for us. It continues bypointing out that relationships of this sort require that theparticipants show each other good will and respect, and that they bejustified in expecting this of one another. Expectations for good willand respect in turn require susceptibility to the reactive attitudes,such as moral resentment, indignation, and gratitude, and inparticular, justified expectations for good will and respectpresuppose that the participants are apt recipients of these reactiveattitudes. But to be an apt target of the reactive attitudes is justwhat it is to be a morally responsible agent. Consequently, that weare morally responsible agents is a necessary condition of thepossibility for us of meaningful adult interpersonalrelationships.

Note that not all the connections among the steps of the argument areplausibly instances of appeals to logical or even metaphysicalnecessary conditions. True, some are: if being an apt target of thereactive attitudes is what it is to be a morally responsible agent,the necessary connection invoked would be conceptual or metaphysical.But if expectations for good will and respect do requiresusceptibility to the reactive attitudes, this would be plausibly acase of nomological necessitation, where the relevant laws arepsychological. But given the sort of skepticism targeted, nomologicalnecessitation is not too weak a connection; it is not called intoquestion by the arguments of the moral responsibility skeptic.

Critics have in effect taken issue with a number of steps of thisargument, for example that expectations for good will and respectrequire susceptibility to the reactive attitudes, and that justifiedexpectations for good will and respect presuppose that theparticipants are apt recipients of the reactive attitudes. Perhapshuman relationships do not require susceptibility to moral resentmentand indignation, but only to the nonreactive attitudes of moralprotest, disappointment, and sorrow (Pereboom 2022). Another avenue ofcriticism involves separating moral responsibility from being an apttarget of the reactive attitudes. It may be that a forward-looking,that is, what Strawson calls an ‘optimistic’ notion ofresponsibility, is all that’s required for good relationships,and it is not characterized by being an apt target of the reactiveattitudes. But these criticisms are controversial, andStrawson’s argument is widely accepted and acclaimed.

Another prominent transcendental argument in the practical sphere isthe sort Christine Korsgaard (1996) develops for Kantian claim that wemust value ourselves as rational agents. Here is Robert Stern’s(2017) representation of one argument of this sort. The initialpremise concerns rational choice, and crucially features the notion ofan agent’s practical identity, the distinctive nature of aperson as an agent, which may include, for example, being a parent ora philosophy professor:

1. To rationally choose to do X, you must take it that doing X is therational thing to do.
2. Since there is no reason in itself to do X, you can take it that Xis the rational thing to do only if you regard your practical identityas making X the rational thing to do.
3. You cannot regard your practical identity as making doing X therational thing to do unless you can see some value in that practicalidentity.
4. You cannot see any value in any particular practical identity assuch, but can regard it as valuable only because of the contributionit makes to giving you reasons and values by which to live.
5. You cannot see having a practical identity as valuable in this wayunless you think your having a life containing reasons and values isimportant.
6. You cannot regard it as important that your life contain reasonsand values unless you regard your leading a rationally structured lifeas valuable.
7. You cannot regard your leading a rationally structured life asvaluable unless you value yourself qua rational agent.
8. Therefore, you must value yourself qua rational agent, if you areto make any rational choice.

Stern (2017) explains this argument as follows. To act is to do orchoose something for a reason. However, an agent has reasons to actonly because of her practical identity; she does not have reasons toact independently of that identity. But a practical identity can yieldsuch a reason only if she regards that identity as valuable. Merelybeing a parent gives one no reason to care for one’s children.Rather, valuing one’s parenthood has this force. At the sametime, an agent cannot regard a particular practical identity asvaluable in itself; Korsgaard argues that this sort of realism aboutvalue is implausible. The only remaining explanation is that sheregards it as valuable because of the contribution it makes toproviding her with reasons and values by which to live. But then shemust believe that it matters that her life has the sort of rationalstructure that having such identities provides. However, to see thatas mattering, she must regard leading a rationally structured life asvaluable. Then, in conclusion, to regard leading such a life asvaluable, an agent must see her rational nature as valuable.

5. Concluding Remarks

The legacy of the arguments such as the Transcendental Deduction andthe Refutation of Idealism includes not only Kant’s actualsuccesses, but also a number of influential philosophical strategies:the now-standard tactic of arguing for concepts whose source is in themind from universal and necessary features of experience; the idea ofdrawing significant philosophical conclusions from premises aboutself-consciousness alone; and the notion of a transcendental argument,which from an uncontroversial premise about our thought, knowledge orexperience, reasons to a substantive and unobvious presupposition andnecessary condition of this claim.

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