1. Systematic unity and purposiveness

Kant’s reflections on systematic unity in the Architectonic of Pure Reason, the final part of the first Critique, are mostly famous as an object of derision. If the aim of this section is to introduce readers to the importance of ‘the art of the system’, it is no exaggeration to say that the artist’s work has traditionally encountered an audience, at best, indifferent, at worst, hostile. All the different elements through which Kant’s analysis unfolds (from the distinction between an aggregate and a system of cognitions to the mysterious references to a schematism of reason, from the link between ideas and ends of reason to the reflection on organisms) have been dismissed without much further analysis.

In The Architectonic of Pure Reason: Systematicity and Purposiveness in the Critique of Pure Reason (Ypi Reference Ypi2021), I set out to do the opposite. I tried to show how its presence in Kant’s first major critical work is not only due to the philosopher’s Liebe für architektonische Symmetrie, as Arthur Schopenhauer maintained in his appendix to Die Welt als Wille und Vorstellung, his Kritik der kantischen Philosophie (Schopenhauer Reference Schopenhauer and Deussen1924: 610–25). Nor is it merely interesting for those who want to engage with aspects of his ‘personality’, as suggested in one of the most authoritative commentaries on the first Critique (Kemp Smith Reference Kemp Smith1962: 579–82). I sought to explain how the interest in architectonic unity was at the heart of Kant’s preoccupations from the initial stages of drafting the first Critique and that this section constituted an organically central, rather than accidental, part of the development of the critical system. Indeed, in a letter to Markus Herz dated November 1776, we find the term ‘architectonic’ mentioned for the first time in connection with Kant’s indication of the different parts of the work that was due to appear under the name of Critique of Pure Reason (10: 199). We also find both the term and the concern with systematic unity present in all of Kant’s other major critical works, for example, in the Critique of Practical Reason, with reference to the relation between the idea of the system and different human faculties, and in The Critique of the Power of Judgement with reference to the necessary systematicity of sciences and the importance of proceeding architectonically and not simply technically in ordering the sum total of our cognitions.

In all these works, the concern for unity in the system seeks to integrate human knowledge and human action, systematicity and purposiveness. More specifically, the Architectonic of Pure Reason tackles directly and with an organic effort the three most important questions that animate Kantian philosophy: What can I know? What should I do? What may I hope? The purpose of the Architectonic – so I try to suggest – is not to simply summarize what the critical system, as outlined in the Critique of Pure Reason, has to say about each of them taken separately. The aim, rather, is to connect the answers to each other in a way that speaks to the general question underpinning all of them: What is the human being?

To answer this question, Kant believes that we ought to recover a notion of philosophy as ‘legislation of human reason’, a legislation which in turn ‘has two objects (Gegenstände), nature and freedom’. They include, on the one hand, ‘the natural law’ (Naturgesetz) and, on the other hand, ‘the moral law’ (Sittengesetz), at first in ‘two separate systems’ but ultimately ‘in a single philosophical system’ (A840/B868).Footnote ¹ Crucial to this project of reunification is the notion of purposiveness, a notion that we find in its most developed form in the Critique of the Power of Judgement – and which I believe paves the way to Kant’s defence of a critical philosophy of history in his later political writings, in his mature theory of right, and in his last writings on religion and virtue. However, in The Architectonic of Pure Reason, I only discuss the third Critique and subsequent works briefly and mainly to contrast their notion of purposiveness with the one we find in the Critique of Pure Reason. The philosophical roots of the more developed concept of purposiveness are in the less developed relation between ideas and ends of reason in the Architectonic of Pure Reason, and without understanding the status of that relation we miss something crucial in Kant’s subsequent body of work.

Therefore, although my primary focus is the pages of the Architectonic, the effort is to explain how the notion of purposiveness is key to understanding the unity of theoretical and practical reason, as well as what kind of metaphysics (dogmatic or critical) ends up grounding that unity. The latter is particularly important because the secondary literature on Kant’s first Critique has often tended to assume either that the first Critique does away with metaphysics altogether or that metaphysics is essential for asserting the primacy of practical reason only. If I am right in my analysis of the Architectonic and how it relates to Kant’s other writings, the traditional sceptical readings of the first Critique and their non-sceptical (or constructivist) counterparts are both limited: they are insufficiently sensitive to the different interpretations of the concept of purposiveness we find in Kant’s body of work, and to the different implications they have for the success of the unifying project as a whole.

As I see it, in the first Critique, the key to the unity of reason is a teleological theory of reason that ends up centred on a concept of purposiveness as design, and this concept of purposiveness as design is one that Kant later abandons in favour of a concept of purposiveness as normativity. While the former authorizes the assumption of a teleology of nature and the endorsement of physical theology, the latter prohibits it altogether, making space for ethical theology instead. To understand this development is to articulate a critical theory of purposiveness, in which the ‘instructive failure’ of the first Critique (as Huber puts it in his contribution to this exchange) is crucial to understanding the unity of reason that Kant always announced but that we only truly find after the third Critique. The aim however is not merely to reproduce the debate on continuities and discontinuities between the first and the third Critique but rather to understand how Kant revives resources available in the German metaphysical tradition (in particular with regard to the role of the ideas of reason and their relation to the idea of God) and modifies them in the course of the development of the critical system as he tries to find a place for an account of purposiveness that does not rely on the traditional metaphysical baggage around physical theology, the idea of intelligent design and the assumption of nature as a system of purposes. The key contribution of an analysis of the problem of the unity of reason, which takes as its starting point the section on the Architectonic of Pure Reason, is the fact that such a reading enables us to move both backwards and forwards: backwards in trying to reconstruct what Kant borrows from his philosophical predecessors, and forwards in terms of outlining the problems that remain open when reflecting on the unity of the system compared to his subsequent philosophical works. The key to Kant’s innovation in the first Critique compared to traditional metaphysics is not so much the abandonment of the former (as in sceptical readings) or the defence of the primacy of practical reason (as in constructivist ones). It is the modification of the function of purposiveness and its overall relationship to transcendental theology which, I suggest, must eventually make way for a critical philosophy of history.

2. The schematism of reason

In his contribution to this exchange Luigi Filieri agrees with me on both the importance of the Architectonic and in the analysis of the principle of purposiveness offered in this section as the key to the unity of Kant’s system. He also agrees with the details of my argument: the main limitation of Kant’s reconciliation of the theoretical and practical uses of reason in the first Critique is that it is achieved through an analysis of purposiveness as design, and that this is in turn due to the absence of a strong link between practical reason and transcendental freedom in the Canon of Pure Reason. His aim is to refine this interpretation by offering a more nuanced account of one crucial element of the Architectonic: the function of the schematism of reason for the unity of the system. In particular, Filieri distinguishes between the schematism of ideas in the Appendix to the Transcendental Dialectic and the schematism of pure reason in the Architectonic, arguing that, while in the Appendix the function of schematism is to bring unity to the multiplicity of cognitions of the understanding, in the Architectonic it is to account for the systematic unity of reason as a whole. I agree with this interpretation, and I agree with Filieri that we should distinguish more carefully between the narrow use of schematism in the Appendix and the wider one in the Architectonic. My point however was to reflect on the more general function of schematism in bridging between heterogeneous elements: in particular the idea of the whole and the multiplicity of parts (in one case the particular laws shaped by the understanding, in the other the sum total of reason’s theoretical and practical cognitions). I also wanted to bring out the role of the principle of purposiveness and its relation to the ideas of reason as the mediating element to which Kant needs to refer in both cases to account for systematic unity. This does not mean that the kind of systematic unity that Kant pursues in the Appendix and in the Architectonic are the same thing, nor is my interpretation committed to eliminating the boundary between the Doctrine of Elements and the Doctrine of Method as Filieri suggests. On the contrary, the book starts with a reminder of the distinctive role of the Doctrine of Method and with an outline of its importance both with reference to Kant’s philosophical predecessors and to the Critique’s overall framework. I also did not mean to suggest that Kant’s effort to ground the unity between the practical and the theoretical use of reason is an utter failure. On the contrary, as I tried to make clear, Kant does succeed but in the absence of a practical domain of freedom, the success comes at a high cost for the critical system. And again, I agree with Filieri that the methodological drive of the Architectonic is prior to – and the condition of – the regulative employment of ideas in the Appendix. But it is precisely because of that priority, which is in turn rooted in a principle of purposiveness insufficiently detached from the ideas of reason, that Kant’s critical project is endangered. Filieri acknowledges that the emphasis on schematism paves the way to a more integrated framework through which the regulative use of ideas within the Appendix rests on the systematic unity between the theoretical and the practical use of reason in the Architectonic. However, I think he downplays the consequences of the absence of a ‘domain’ for the practical use of reason, including the consequences for the argument he himself wants to make, namely that in the Architectonic of Pure Reason ‘there is no need for a deduction of the ideas’ since all that we need is ‘the practical employment of reason itself’. But this is exactly my question: what is the practical use of reason grounded on in the first Critique? In the absence of transcendental freedom, its architectonic-systematic drive rests – as I try to suggest – on shaky grounds.

3. Autonomy and legislation

In her contribution to this exchange, Sofie Møller acknowledges the force of this question and helpfully distinguishes between different aspects of the practical use of reason. As she argues, the term ‘legislation’ can be ambiguous between two different interpretations of the role of practical reason: one that emphasizes the source of norms and the other their imposition as binding. Comparing my account with other constructivist interpretations of Kant’s Architectonic, Møller rightly points out that while all these readings emphasize the role of the practical for the unity of Kant’s system, I am sceptical that this role can be properly vindicated without the notion of autonomy and transcendental freedom that emerge in Kant’s later works. Let me explain.

On the familiar constructivist accounts, the architectonic unity of Kant’s system is vindicated reflexively. We think of reason as involved in building work, where we have a plan and a series of cognitions that we must order (following Kant’s suggestions in his Doctrine of Method). This requires in turn that we have an architectonic plan and that the plan be guided, first, by discipline in the selection of the tools deployed in the process of construction, secondly, by our practical interest in showing that the construction procedure can produce moral principles, and thirdly that the discipline and interest of the enterprise be combined in a unique system able to generate norms that are binding for finite agents like us (see for a reading of this kind O’Neill Reference O’Neill1989). The first task is therefore negative: we ought to rule out reasons that attach to particularistic motivations and fail to meet standards of appropriate generalization (in Kantian terms, we have to exclude maxims that we cannot will to be laws). Call this the discipline requirement. The second is positive: we are guided by principles that promote our rational nature as reflected in the ability to set and pursue ends that can be generalized. Call this the rational interest requirement. Finally, the negative and positive constraints lead to a third one, a demand for the coherent integration of the discipline and interests of reason in a self-validating unitary system. Call this the architectonic requirement. This latter, architectonic requirement is satisfied when the norms constructed fit in a systematic whole which remains the product of autonomous agency (i.e. requires no dogmatic credo) whilst retaining its lawlikeliness (i.e. does not lead to scepticism about their source and validity). Notice that the third, architectonic requirement, cannot be reduced to a simpler or more intuitive formulation of the first two: what is at stake here is not simply finding a concept that enables us to put theoretical unity and practical unity side by side without contradiction, but the unity of the entire system (both theoretical and practical), encompassing the realms of nature and freedom. My point is that in the absence of a strong link between moral normativity and transcendental freedom, the architectonic requirement can only be satisfied with reference to the idea of God. This means that, at this juncture, the unity of the system cannot be said to be vindicated reflexively. Instead, it is justified metaphysically, through the link between the concept of purposiveness, the unifying function of the ideas of reason and the postulate of nature as a purposive system.

4. The role of God in the system

In her contribution, Møller distinguishes between two different approaches to the role that the idea of God plays in relation to the practical use of reason: a stronger and a weaker justification. They are distinguished by the epistemic attitudes developed in each case: one theistic and one agnostic. On the theistic reading, the postulate of God slides into dogmatic metaphysics in so far as the idea of God is essential to the foundation of moral normativity in the first Critique. On the agnostic reading, the question is one of practical faith, and belief in God is necessary to give binding force to moral norms that satisfy reason’s independent moral demands. Therefore, as Møller argues, the first Critique may be able to account for the unity of reason ‘through a subjectively necessary yet objectively insufficient belief in God’. Such practical belief in God, she clarifies, is essential for the moral law to be binding on people like us but should not be confused with a dogmatic metaphysical claim about God’s existence. I shall return to this point when I discuss the epistemic status of the physico-theological argument for the existence of God, and its relation to nature as a system of purposes. For now, it is worth emphasizing that a similar point also returns in Jakob Huber’s contribution, where he explains the difference between two different propositional attitudes: ‘knowledge’, on the one hand, and ‘faith’ on the other. The latter, he argues, is a strong kind of assent which we are permitted to hold without ‘sufficient objective ground’ but simply on the basis of practical needs.

I agree with Huber that practical belief is an important propositional attitude in Kant, that it is distinct from knowledge and that it is more than mere opinion. And I agree that while a theistic approach to the question of God does occasionally appear in the first Critique, it is the more agnostic perspective developed out of commitment to the practical use of reason that we should be focused on. That is indeed one of the reasons why, when discussing the connection between the source of moral normativity and the problem of the consequences of moral action, I focus not so much on the psychology of action and the motivational background that underpins practical requirements (as Huber urges me to do) but on the demands of rational consistency. The question both Huber and Møller raise however remains valid regardless of these further refinements: does my interpretation downplay the contribution of the first Critique if we can simply appeal to practical faith as the foundation of the architectonic unity of the system?

5. Rational faith in what?

To answer this question, we need to delve into the details of Kant’s analysis of purposivenesss in the first Critique and understand its evolution in the successive body of work. Let us assume that the practical use of ideas and rational faith are sufficient to justify the unity of the system. The point I am raising is not epistemological, it is metaphysical: it has not to do with the degree of confidence with which we can establish certain assumptions about the unity of the system but with the problem of what those assumptions are grounded on. In the absence of transcendental freedom, I suggest, the unity of the system is linked to a principle of purposiveness as design, which is ultimately rooted in an assumption of nature as a purposive system. This may not be such an important difference if we read Kant backwards, as many constructivists do, projecting on the first Critique what we know from the second and third. Indeed, when Huber challenges my claim that ‘human beings must pose their moral ends in the phenomenal world assuming that at least the possibility of a harmonic unity between such ends and the laws of nature is given’, he invokes the concept of hope as the ground for our commitment to the possibility of realizing the Highest Good. However, to motivate ‘hope’ Huber appeals not to Kant’s first Critique but to his late political writings and to his Doctrine of Right. In these texts, as is well known, Kant defends the possibility of moral progress in history by arguing for a much weaker condition of warranted assertability: roughly, the proposition that says that the realization of the highest good is possible provided we cannot show that it is impossible. All this is eminently plausible. But it is not Kant’s position in the first Critique.

To understand why, we need to explain what has changed in Kant’s analysis of purposiveness. The ‘weaker and metaphysically less contentious modal connection between theoretical and practical commitment’ to which Huber is drawn is only available to us once we have clarified the status of the principle of purposiveness and its relation to the idea of nature as a system of purposes. This is where my interpretation comes in. There is ample textual evidence to support the claim that Kant’s views on the transition from the legitimate (critical) use of the principle of purposiveness to the justification of physico-theology not only evolved but changed radically. But if Kant’s position on purposiveness remained consistent throughout, if there was no danger of slipping into dogmatic metaphysics, if there were no implications for the unity of reason, why did that change occur?

My argument is that this is due to an ambiguity in the use of the principle of purposiveness, which in the first Critique is rooted in the theory of intelligent design, and in later works is not. It is because of this connection between the concept of purposiveness rooted in the ideas of reason, and nature as a system of purposes, that Kant believes we can move from the practical use of reason to the validity of physico-theology. It is because of this connection that the final end (Endzweck) of nature can be schematized in the Architectonic. ‘All research into nature’, Kant argues in the first Critique, ‘is thereby directed toward the form of a system of ends, and becomes in its fullest extension physico-theology’ (A816/B844).

Now consider the contrast with the Critique of the Power of Judgement. ‘Physicotheology’, Kant argues there, ‘no matter how far it might be pushed, can reveal to us nothing about a final end of creation; for it does not even reach the question about such an end’ (KU, 5: 436). If the argument about practical faith remains unchanged in the first and third Critique, and the implications for Kant’s wider metaphysical commitments are as my critics suggest, why does his stance on the final end of nature change so dramatically, and why does he go to such lengths to explain its implications for the assessment of the unity of the system?

In the Critique of the Power of Judgement, physico-theology, the argument that moves from the use of a purposive principle in reflecting about the unity of the system to the assumption of nature as a system of purposes, is explicitly ruled out. Kant here explains that nature, as such, never favours humanity over other animals. He asserts that humans are not exempt from its destructive effects whether in the form of pestilence, hunger, floods, cold or attacks from other animals. While one might argue that, from a different epistemic standpoint, these circumstances might also be seen to serve higher purposes and promote moral demands, Kant takes a different approach. He argues that the focus should not be on what nature does for humans but what humans do with nature to develop their moral ends.

Unlike the Architectonic of Pure Reason where the idea of God is schematized and mediated with reference to a principle of purposiveness, in the third Critique there is only one idea of reason which warrants practical faith: that of freedom understood as a fact of reason. In this context, the various types of knowledge – scientific, artistic, political, legal, religious and social – that humans produce over many generations are building blocks in a system of reason that develops historically but is analysed philosophically with the help of a theory of moral freedom. To meet the systematic requirements of reason and explain how nature and freedom can be integrated in a unitary system, the third Critique focuses not so much on the idea of God but on the collective dimension of the duty to realize the Highest Good in the world. This however can only be achieved once the connection to transcendental freedom is clarified, something Kant is unable to provide in the first Critique. Once the causality of freedom is established, Kant turns definitively to the history of reason to understand how the principle of purposiveness shapes our orientation in it. However, for this process of self-knowledge to be considered authoritative and cumulatively fruitful, reason’s capacity for self-improvement must be sustained. The question arises: how can this be justified? What type of practical faith is at stake here?

As mentioned at the outset, one option is to assume that nature will aid reason in this task. However, this strategy is flawed, as reason would overstep its boundaries by claiming to know nature’s intentions and asserting that everything in the world exists for the sake of human beings or that humans are the ultimate end of nature. An alternative strategy involves turning to reason’s own history, and looking at the way it realizes its purposes in the external world. This requires a shift in perspective, akin to the Copernican revolution, regarding reason’s past, present and future: transcendental freedom is the key to a teleological historical orientation, and reflexive judgement rather than the idea of God is the anchor on which the unity of the system is based.

What does this change in perspective entail? And does it really not matter whether that practical faith is directed to the idea of God or to a philosophical history of humanity? To repeat: I am not disputing my critics’ argument that ‘hope’, ‘practical faith’, ‘rational belief’, etc. are important propositional attitudes here. My question is: what is the object of hope? My answer is that this object changes during the development of Kant’s theory of purposiveness. Kant moves from an account of nature as purposefully oriented to adopting a heuristic approach, whereby the process of reason’s self-explication is validated by observing how reason influences and transforms the historical world. Kant starts with a philosophy of nature centred on the architectonic idea of God but ends up embracing a philosophy of history centred on the fact of reason. This is also why, when in his later political writings Kant raises the question of moral progress, and wonders if it is possible to find a ‘sign’ of it in the historical world, he invokes not nature but history, not animals and plants but human beings and the standpoint from which they judge the political events of their time.

Here the conception of purposiveness as design with which Kant started in the first Critique turns definitively into a conception of purposiveness as normativity. Only a principle of purposiveness as normativity can disentangle purposiveness from physico-theology, and only once physico-theology becomes irrelevant to the unity of the system are we able to understand why Kant insists that we should not think of ourselves as ‘nature’s special favourite’ (KU, 5: 430). Purposiveness as normativity enables us to properly integrate the two domains of the legislation of human reason, the theoretical and the practical, without slipping into the ambiguity that the Architectonic could not avoid. It is only at this point that the answer to the question ‘What is the human being?’, which encapsulates the other three fundamental questions of philosophy (What can I know? What should I do? What may I hope?) dissolves the issue of compatibility of our ends with those of nature into the open-ended search for a philosophy of history. And it is only at this point that the question of practical faith in God turns irreversibly into a demand for practical faith in humanity.