Critique and Transformation: On the Evolution of Kant’s Conception of God and Its Internal Roots

Abstract

Generally speaking, the conception of God serves as the theoretical focal point and central concern of Kant’s philosophy of religion. Its content is multidimensional, covering many aspects, such as proof of God’s existence, the image of God, and God’s status and functions. The purpose of this paper is to examine the evolution of the concept of God in Kant’s philosophy of religion in three different philosophical periods—the pre-critical period, the period of the critical philosophy and the post-critical period—to analyze the evolution of the internal contradictions in Kant’s philosophy of religion and the course of its systematic construction, and, on this basis, to reveal the three pivotal systemic transformations achieved by Kant’s philosophy of religion—the deconstruction of traditional theology, the reconstruction of rational theology and the construction of moral religion. Finally, this paper elucidates four internal roots which drive these pivotal transformations: (1) methodological foundation: the development of critical philosophy; (2) systematic goal: the establishment of scientific metaphysics; (3) axiological orientation: the secularization of theology into anthropological theology; and (4) practical culmination: the extension of pure moral philosophy.

1. Introduction

Kant’s philosophy was formed at a particular time when Enlightenment reason challenged traditional Christian beliefs, when natural science was arising and traditional theology was declining, and when the myth of dogmatic metaphysics was shattered by skepticism. Being deeply imbued with pietism on the one hand, and born out of the Leibniz-Wolff System, Hume’s skepticism and Spinozist philosophy on the other, the tension between reason and faith throughout Kant’s philosophical reflections on religion and was centrally displayed in the evolution of the conception of God1 in Kant’s philosophy of religion. The purpose of this paper is to examine the inherent tension between reason and faith in Kant’s philosophy and its concrete manifestations across the pre-critical, critical, and post-critical periods.2 By analyzing Kant’s proposed solutions to these tensions, this study aims to reveal how Kant’s philosophy of religion, through continuous critique and self-critique, accomplished three pivotal transformations in his conception of God. These transformations ultimately realized the dual ideals of establishing scientific metaphysics and secularizing theology into anthropological3 theology—a synthesis fully articulated in his system of moral religion. The evolution of the conception of God, as the central focus of this investigation, serves as the unifying thread connecting the entirety of Kant’s religious philosophy.

Numerous studies have addressed the evolving conception of God in Kant’s philosophy. Following the structure of this paper, the relevant literature may be classified into three developmental phases—the pre-critical, critical, and post-critical periods—which both reflect Kant’s intellectual trajectory and help organize the academic genealogy that underpins this study. This taxonomy also enables readers to locate relevant scholarship within the framework this paper seeks to construct.

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Pre-Critical Period:

F. E. England’s Kant’s Conception of God (England 1968) is a foundational work that focuses on Kant’s early critique of the Leibniz-Wolff system. England analyzes how Kant adopted logical strategies to reject the claims of traditional metaphysics regarding divine knowledge and replaced them with a novel metaphysical teleology grounded in moral purpose. This transformation represents a pivotal shift in Kant’s conception of God in the pre-critical phase. England’s analysis is closely aligned with the present paper’s interpretation of Kant’s first transformation: namely, the logical dismantling of dogmatic theology, marking Kant’s initial move away from classical metaphysical theism.

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Critical Period:

Allen W. Wood’s Kant and Religion (Wood 2020) marks his return to Kant’s religious philosophy after more than five decades. This comprehensive study spans all three periods of Kant’s thought and engages deeply with his major works, including the three Critiques and Religion within the Boundaries of Mere Reason. Wood emphasizes the necessity of God as a postulate of practical reason, and explores the structural role that faith plays in the development of Kant’s ethical rationalism. These insights resonate strongly with the current paper’s focus on Kant’s second transformation—the repositioning of God from epistemic object to moral postulate—as developed in the Critique of Practical Reason and related works. Wood’s work helps substantiate and further enrich this paper’s interpretation of God’s regulative function in Kant’s critical period.

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Post-Critical Period:

Two indispensable studies must be mentioned here: Michael Forster’s Kant’s Final Synthesis: An Essay on the Opus Postumum (2000), and Samuel Kahn’s Kant’s Post-1800 Disavowal of the Highest Good Argument for the Existence of God (2020). Forster argues that Kant’s Opus Postumum represents a comprehensive final synthesis of his entire philosophical project—including his religious philosophy—wherein Kant not only reconsiders certain earlier positions but also demonstrates a new tendency to address long-standing tensions (such as between freedom and necessity) within a unified theoretical structure. Kahn’s study, in contrast, challenges the continuity of Kant’s commitment to the postulate of God by questioning whether Kant after 1800 still affirmed the necessary connection between the highest good and the existence of God. Both works are thus deeply relevant to this paper: although they do not necessarily support the present thesis, they provide essential interpretive frameworks and raise critical questions that broaden the theoretical scope of the inquiry. Their inclusion extends the conversation beyond the bounds of doctrinal alignment and into a richer terrain of philosophical dialogue. Additionally, Allen Wood’s early work Kant’s Moral Religion (Wood 1970) did not directly address Kant’s conception of God, its emphasis on Kant’s philosophy of religion and its incisive analysis of Kant’s system of moral religion provided a critical support for this study.

Based on these, the purpose of this paper is to systematically sort out and summarize the evolution of Kant’s conception of God from the pre-critical period to the post-critical period, so as to clarify how Kant realized three pivotal transformations, i.e., the deconstruction of traditional theology, the reconstruction of rational theology, and the construction of moral religion through critique and self-critique, and finally analyzed and examined the internal roots of the transformations in Kant’s conception of God.

2. The First Transformation in Kant’s Conception of God: The Deconstruction of Traditional Theology in Kant’s Pre-Critical Period

The conception of God in Kant’s pre-critical period both inherited the rationalist tradition of dogmatic metaphysics which attempted to prove the existence of God through logical deduction, and stepped out of the dogmatism under the impact of the emerging skepticism; and it retained the traditional conception of scholastic philosophy, but also showed the tendency of Deism. This tension influenced Kant’s philosophical thinking on religion in his pre-critical period, prompting Kant to critique the Cartesian and Wolffian proofs of God’s existence and respond to the personified conception of God, and in doing so to complete the deconstruction of traditional theology and to realize the first pivotal transformation in his conception of God.

Specifically, Kant firstly epistemologically rejected the ontological mode of proof employed by dogmatic metaphysics. And at the cosmological level, he turned to a moderate form of Deism to negate radical pantheism and reconcile its conflict with personified theism. In The Only Possible Evidence for the Existence of God (hereafter referred to as Evidence) which was published in 1763, Kant focused his criticism on the Cartesian ontological proofs, attributing the error of this traditional way of proving the existence of God to its misuse and confusion of the concept of “existence”. Kant explicitly stated that “existence,” as a predicate, could only be regarded as a “logical predicate” and not a “real predicate.” The distinction between the two lies in the fact that a “logical predicate” merely establishes the relation between a concept and its empirical object without expanding the concept’s content, whereas a “real predicate” adds substantive attributes to the concept. During this period, Kant summarized the Cartesian ontological proof as follows: (1) God is a being with absolute perfection; (2) Existence is a perfection; (3) Therefore, God’s perfection includes existence, and thus God exists. It is evident that this line of argument directly contradicted Kant’s analysis of the concept of “existence”—namely, that Descartes treated existence as a “real predicate,” thereby expanding the content of the subject “God.” Consequently, Kant argued that the Cartesian ontological proof committed a logical error and thus remained untenable. However, Kant was not content with mere critique and negation, or rather he did not completely reject all forms of ontological proofs. After completing his critique of the Cartesian ontological proof, Kant put forward his own proof of the existence of God, that is, he attempted to re-examine the feasibility of the ontological proof from the point of view of the “conditions of possibility”. Specifically, by analyzing the concepts of necessity and possibility, Kant turned to the “the intrinsic possibility of things” in an attempt to find a different path from Descartes’ concept of “perfection”. This proof, which Kant regarded as “the only possible proof for the existence of God”, can be summarized as follows:

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The intrinsic possibility of everything presupposes the existence of something;

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It is impossible for nothing to exist;

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Things have intrinsic possibilities;

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An absolutely necessary Being is a thing that has an inherent possibility;

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This being which is the intrinsic possibility of all things presupposes precisely this absolute necessity of Being;

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Therefore, the absolutely necessary Being exists (see Kant 1905, AA 2, pp. 77–98).

Kant identified this absolutely necessary Being as singular, immutable, eternal, and simple (indivisible), thus attributing to its essence the nature of a spiritual substance. It reveals that Kant’s proposed ontological proof diverges from the Cartesian ontological proof in a critical respect: the former deduces God’s reality from the perfection inherent in conceptual attributes, constituting an analytic judgment, whereas the latter infers God’s existence as a necessary condition from the possibility of experience, thereby containing an ontological presupposition. Kant, at this stage, failed to recognize that this ontological proof based on “conditions of possibility” itself implied an ontological presupposition that remained unproven. The crux of this proof lies in bridging the leap from possibility to existence, for possibility, being a cognitive form, does not directly equate to existence; one cannot conclude the existence of a thing from its intrinsic possibility. Notably, despite their differing deductive paths, both proofs rely on conceptual-logical derivation and thus constitute a priori proofs. Thus, Kant’s proof based on conditions of possibility, while advancing beyond previous proofs of God’s existence to some extent, still does not completely escape from the logical framework of the Leibniz-Wolff system; it remains an a priori analysis based on concepts. Kant later further examined and criticized it in the Critique of Pure Reason. “Sein ist offenbar kein reales Prädikat, d. i. ein Begriff von irgend etwas, das zu dem Begriffe eines Dinges hinzukommen könnte. Es ist nur die Position eines Dinges, oder gewisser Bestimmungen an sich selbst.” (Being is obviously not a real predicate; that is, it is not a concept of something which could be added to the concept of a thing. It is merely the positing of a thing or of certain determinations in themselves.) (Kant 1911, AA 3:401) (Critique of Pure Reason). Just as Allison argued in Kant’s Theory of Freedom, Kant’s proof of God at this stage remained a ‘dogmatism in critical disguise’, whose innovativeness was confined to the methodological level without touching the foundation of metaphysics (see Allison 1990, pp. 230–36).

In addition to proposing his own ontological proof, Kant also advanced a cosmological proof for God’s existence during his pre-critical period. In his 1755 work Universal Natural History and Theory of the Heavens, he described God as “the ultimate cause of the beauty and order of the cosmic edifice” and likened God to “the most skilled watchmaker,” thereby portraying “nature” as a precision instrument operating according to divinely ordained laws. Furthermore, in Evidence, Kant introduced an alternative approach to proving God’s existence distinct from the a priori path—namely, the “a posteriori path of cognition.” This epistemological route begins with the possibility of the empirical world to discern its universally necessary order, where the harmonious unity and perfect organization of the world unmistakably attest to the existence of God as its designer. However, it is crucial to recognize that this cosmological proof differs from occasionalism or the theory of pre-established harmony. Since God, as the “ultimate cause of cosmic order,” inherently possesses “transcendent wisdom,” any arbitrary intervention beyond universal laws becomes superfluous. In other words, God, in a single act, designed the laws governing all things in the universe and thereafter refrained from interfering with their natural operations, never displaying His wisdom or will capriciously. This cosmological proof unmistakably reveals Kant’s deistic4 leanings, enabling him to dissociate from radical pantheism while eliminating remnants of a personified God, thereby completing his shift toward a moderate form of Deism. Yet, Kant failed to recognize that both the cosmological proof he critiqued and the deistic proof he subsequently constructed fundamentally misuse the principle of causality—illegitimately extending a law applicable only to phenomena into the realm of divine concepts. For instance, the proof begins with the “contingency” of the cosmos but concludes with a “necessary being” as its endpoint, presupposing that “the possibility of things must have a real ground,” thereby conflating logical necessity with causal necessity. Thus, his critiques and reconstructions during this period never addressed the root flaws of cosmological proofs, including: (1) Misapplication of logical categories; (2) Circular reasoning; (3) Confusion of the empirical and the transcendent; (4) Equivocation between logical and causal necessity.

However, insofar as the pre-critical period is concerned, on the basis of his deconstructing of dogmatic metaphysics represented by the Leibniz-Wolff System and Cartesian ontological proofs, with presenting a strengthened ontological proof based on the “conditions of possibility” and a cosmological proof with an implicit tendency of Deism, Kant tentatively resolved two major contradictions confronting the philosophical system of his own pre-critical period—the opposition between the rationalist tradition of dogmatic metaphysics and skepticism, and the opposition between the personified theism of traditional theology and the rational theology as represented by Deism—and achieved a critique of traditional theology and completed the first transformation in his conception of God. This marked his initial deconstruction of traditional theology and the first transformation in Kant’s conception of God.

However, this critique and reorientation remained incomplete. Firstly, Kant failed to escape the dream of dogmatic metaphysics completely, and the new ontological proof he put forward are only variations of the “law of sufficient reason” of the Leibniz-Wolff System, whose essence was still tied to logical deduction and a priori analysis, which equated possibility with reality. Kant’s denial of the logical validity of the traditional way of proving was merely an attempt to replace it with a more sophisticated and superior logical method. Secondly, although Kant dissolved the personified conception of God by redefining divinity as the cosmic designer, this idea itself implied a remnant of moral teleology, in which the order of the world was attributed to a transcendent intelligence with divine rationality. The image of God here was split into two facets, an impersonal natural lawmaker on the one hand, and a moral legislator beyond human reason on the other. The resulting paradox is that God, as the institutor of natural laws, requires demonstration through logical deduction or empirical proof, demanding more explicit arguments for God’s reality. Whereas if God is the legislator of the moral order, His existence can be apprehended solely through faith without additional rational demonstration— yet this does not imply that God as moral legislator is inaccessible to reason.

Moreover, the conception of God of Deism requires that God does not intervene in the workings of nature, whereas God, as the legislator of the moral order, must reward and punish human beings for good and evil. Ultimately, during the pre-critical period, Kant had already begun to realize—under the shadow of skepticism—the limits of human reason. Therefore, he had to press forward to explore the boundaries of reason until he could divide the objects of knowledge into those accessible and inaccessible to human cognition. In this process, the idea of God was identified as a transcendental ideal beyond the reach of reason, and all epistemological expectations regarding God were abandoned—thus achieving a revolution in the epistemological sense. Therefore, the only way to make ground for faith is to scrutinize reason itself and re-establish the boundaries of knowledge. It should be said that the first critique and transformation were both a deconstruction of traditional theology, a prelude to the critical philosophy, and the final dirge of dogmatic metaphysics.

3. The Second Transformation in Kant’s Conception of God: The Reconstruction of Rational Theology in the Period of Kant’s Critical Philosophy

Nonetheless, Kant’s philosophical reflection on religion continued to face three unresolved issues: (1) The enhanced version of the ontological proof presented by Kant in the Evidence has still not completely escaped from the influence of dogmatic metaphysics and thus fully transcend its conceptual framework. (2) As previously discussed, Kant failed to completely reconcile the conflict between Deism and the personified theism, and the conception of God took on the dual orientation of designer of natural law and legislator of moral order. (3) The shadow of skepticism still hovered over human reason, the limits of which have yet to be further clarified. In 1770, Kant published On the Form and Principles of the Sensible and Intelligible World, which marked his formal entry into the period of his critical philosophy. It is in his critical philosophy, specifically in the Critique of Pure Reason, that Kant attempted to achieve a reconstruction of rational theology through critique.

Specifically speaking, regarding issues (1) and (3)—the thorough elimination of dogmatic residues within the philosophical system and the demarcation of human reason’s boundaries—Kant addressed these through his epistemological inquiry, culminating in the “Copernican Revolution” in epistemology as articulated in the Critique of Pure Reason. Kant recognized that the impasse of traditional epistemology lay in reason’s limited cognitive capacity. Inspired by natural science, Kant proposed that the center of epistemology should be shifted from the object to the subject, with asserting that “objects must conform to knowledge” rather than the traditional “knowledge conforming to objects”, thereby inverting the classical epistemological paradigm. Kant articulated this basic transformation as follows: “Bisher nahm man an, alle unsere Erkenntnis müsse sich nach den Gegenständen richten… Man versuche es daher einmal, ob wir nicht in den Aufgaben der Metaphysik damit besser fortkommen, daß wir annehmen, die Gegenstände müssen sich nach unserem Erkenntnis richten Es ist hiermit eben so, als mit den ersten Gedanken des Kopernikus bewandt… der, nachdem es mit der Erklärung der Himmelsbewegungen nicht gut fort wollte, wenn er annahm, das ganze Sternheer drehe sich um den Zuschauer, versuchte, ob es nicht besser gelingen möchte, wenn er den Zuschauer sich drehen ließ und dagegen die Sterne in Ruhe.” (Hitherto it has been assumed that all our knowledge must conform to objects… We must therefore make trial whether we may not have more success in the tasks of metaphysics, if we suppose that objects must conform to our knowledge… This would agree better with what is desired, namely, that it should be possible to have knowledge of objects a priori… Here then is a similar experiment to that of Copernicus… Failing of satisfactory progress in explaining the movements of the heavenly bodies on the supposition that they all revolved round the spectator, he tried whether he might not have better success if he made the spectator to revolve and the stars to remain at rest.) (Kant 1911, AA 3, pp. 12–13) (Critique of Pure Reason). The core task of this epistemological “Copernican Revolution” was to define the cognitive capacity of reason and to delimit its proper domain—two interrelated processes carried out simultaneously. What Kant calls the sensible world is the empirical domain grasped by the cognitive subject through the a priori forms of intuition provided by sensibility and the a priori categories provided by the understanding. In contrast, the intelligible world refers to the domain in which reason is incapable of producing valid knowledge. Traditional metaphysical concerns—such as God, freedom, the soul, and the cosmos—belong to this realm. By drawing clear boundaries for reason, Kant was thus able to liberate metaphysics from dogmatism and establish a secure foundation for a scientific metaphysics. This “Copernican Revolution,” by inverting the subject–object cognitive relation, redefined the subject as the legislator of knowledge and restructured humanity’s understanding of cognition. While creating conceptual space for natural science, it simultaneously reserved a domain for theological faith.

Building upon this foundation, Kant subjected the ontological method of proving God’s existence through “conditions of possibility,” as proposed in his pre-critical work the Evidence to meticulous scrutiny and critique. He further subdivided the traditional theological-metaphysical proofs for God’s existence to dismantle their foundations at a deeper level. In the Critique of Pure Reason—a pivotal text of his critical philosophy—Kant repudiated the reinforced ontological proof he had earlier advocated in the Evidence. By drawing selectively on his earlier critiques of other proofs, he systematically dismantled all remaining avenues for demonstrating God’s existence. Specifically, Kant redefined God in the Critique of Pure Reason as an unknowable “transcendental ideal”—a necessary idea of pure reason, an immaculate supreme ideal, inherently inaccessible to human experience. Such a conception of God lies beyond the bounds of human reason and cannot be known through rational cognition. Once God was excluded from the domain of human knowledge, all attempts to prove the existence of God through reason amounted to a transcendental overreach. The “conditions of possibility” approach employed in the pre-critical period was precisely such an overreach, as it conflated the distinction between logical possibility and real (ontological) possibility. Here, Kant refined the logical implications of “existence” by distinguishing between its role as a real predicate (adding determinate content to a concept) and a logical predicate (merely positing a concept’s relation to experience). He asserted that logical possibility required only the absence of conceptual contradiction, which did not entail real actuality. Kant famously illustrated this point with the example of a hundred thalers, i.e., the concept of a hundred thalers holds no greater logical significance than the actual hundred thalers, yet their existential implications differ entirely. Thus, while reason might coherently define God through the concept of supreme reality, such conceptual consistency could not confer actual existence. For Kant, God maybe remains a “mere fiction” or a “flawless pure ideal” not empirically real.

By constraining reason’s jurisdiction, Kant confined the transcendental ideal of God strictly within the intelligible world, prohibiting its illegitimate extension into the domain of objective actuality. This critique conclusively dismantled his earlier ontological proof from the Evidence. Regarding other proofs for God’s existence, Kant adopted a unified critical approach. He subsumed both deistic and cosmological proofs under the ontological framework, by arguing that all such attempts presupposed reason’s capacity to cognize the noumenal, thereby generating transcendental illusions. He further demonstrated that deistic proofs merely repackaged cosmological arguments, which themselves ultimately relied on ontological presuppositions. Consequently, Kant concluded that all proofs for God’s existence are fundamentally ontological in nature. Having already undermined the ontological proof’s foundations through his analysis of “existence” and the limits of reason, Kant thereby invalidated all dogmatic-metaphysical attempts to prove God’s existence.5

Regarding issue (2)—namely, the conflict between the dual aspects of the concept of God inherited from the pre-critical period, that is, between Deism and personified Theism—Kant divided the sensible world and the intelligible world, and redistributed God’s distinct functions across the domains of theoretical and practical reason. This strategic separation avoided a direct opposition between the two within his philosophical system and achieved a dialectical synthesis of God’s natural and moral attributes. As a result, God functioned simultaneously as the guarantor of teleological purposiveness in the realm of nature and of moral actuality in the domain of ethics. Specifically, in the Critique of Pure Reason, Kant regarded God as a “transcendental ideal” and excluded all knowledge of God from the scope of human cognition, thereby treating God purely as a “regulative principle of natural teleology.” This principle’s function is strictly limited to guiding natural science toward the pursuit of systematic unity. Although Kant inherited the methodological legacy of Deism, he retained only its heuristic value. In the Critique of Pure Reason, Kant denoted God to be a “transcendental ideal”—a regulative principle of natural teleology—whose role was strictly confined to guiding scientific inquiry toward systematic unity. While inheriting Deism’s methodological framework, Kant stripped it of ontological commitments, by relegating God to a heuristic device for organizing empirical knowledge. The concept of the “regulative principle” is a central methodological tool in Kant’s critical philosophy. Kant distinguishes between two modes of employing reason’s principles: “constitutive principles” and “regulative principles.” The latter do not construct empirical objects but serve as rational guidelines for organizing knowledge. As Kant makes clear: “Regulative Prinzipien … sind nicht objektiv, sondern bloß subjektiv gültig, d.h. sie geben kein Objekt an, sondern nur die Richtung, in welcher man es suchen soll, um die systematische Einheit der Erkenntnis zu erlangen.” (Regulative principles … are not objectively valid, but only subjectively valid, i.e., they do not pertain to the object, but only to the direction or rule in accordance with which a unity of experience can be brought about in our cognition.) (Kant 1911, AA 3, p. 657) (Critique of Pure Reason). Hence, ideas like God, which do not refer to empirical objects of knowledge, can still serve a guiding and organizing role within rational inquiry through the use of regulative principles. In Kant’s critical system, regulative principles play a key unifying function: they direct human cognition to regard objects as parts of a total system and thus facilitate the pursuit of systematicity. Through them, Kant regulates the legitimate and illegitimate uses of reason, explaining how transcendental ideas—though not empirically constructive—can nonetheless exert a positive influence on cognition. It is important to note that since regulative principles are not directly tied to empirical objects but are used as subjective maxims, they possess only subjective necessity rather than objective reality. In this way, Kant’s epistemological method is further clarified and refined. The antinomies of reason—including those concerning nature and freedom—can thus be resolved through this framework. Like God, understood as a “regulative principle of natural purposiveness,” other non-empirical ideas can similarly function to promote the coherence of rational knowledge and provide heuristic direction for empirical research. As Kant writes: “Denn ohne diese regulativen Prinzipien würden wir, wie wir noch zeigen werden, in der empirischen Untersuchung keinen Zusammenhang, keine systematische Einheit, also keinen Leitfaden zur empirischen Erkenntnis haben.” (For without these regulative principles we would have no guideline at all for empirical inquiry, and thus no connection of empirical cognitions into a whole, hence no systematic unity of empirical cognition, as we shall show later.) (Kant 1911, AA 3, p. 668) (Critique of Pure Reason).

In the Critique of Practical Reason, Kant presented God as “a supreme rationality legislating moral law.” Although expelled from the domain of knowledge and relegated to the status of a transcendental ideal beyond the reach of human cognition, this did not render the concept of God meaningless or dispensable. On the contrary, while epistemologically inert, God plays a crucial role in the domain of practical reason, where He becomes a necessary postulate. Kant argued that practical reason’s pursuit of the highest good (summum bonum)—the unity of virtue and happiness—requires the postulates of God’s existence, free will, and the immortality of the soul in order to make the realization of moral ends possible. Even in the Critique of Practical Reason, these three postulates are not treated as objects of knowledge subject to rational proof, but as necessary assumptions made by the moral law for the sake of its own fulfillment. Thus, although God functions here as a “moral legislator” who secures the ultimate realization of moral goals, He is neither personified nor intervenes in the empirical world. Rather, God remains a theoretical construct that ensures the meaningfulness of moral action, without being assigned objective reality. In this way, God, though banished from epistemology, finds a rightful place within moral practice. In the Critique of Pure Reason, Kant had already revealed through the third antinomy the conflict between freedom and natural necessity. In the Critique of Practical Reason, he reassigns God the role of mediator between the two, affirming God’s practical function while denying His ontological status. In doing so, Kant achieves a balance across distinct functional domains—God remains unknowable in theory, yet indispensable in ethics. Just as Kant said: “Ich mußte also das Wissen aufheben, um zum Glauben Platz zu bekommen.” (I had to deny knowledge in order to make room for faith.) (Kant 1911, AA 3, p. 19) (Critique of Pure Reason) Thus, God’s bifurcated identity—natural teleologist and moral guarantor—could be found having a kind of equilibrium: exiled from epistemology, God was resurrected in ethics, by securing both the intelligibility of nature and the meaningfulness of moral action.

Overall, by defining the cognitive capacity of human reason, Kant first carried out the epistemological “Copernican Revolution,” overturning the paradigm of cognition. On this foundation, he deepened his critique of dogmatic metaphysics and traditional theology, thereby fully disentangling his philosophy from the entanglements of both dogmatism and skepticism. Ultimately, by distinguishing the functions of God within the theoretical and practical domains of reason, Kant reconstructed a conception of divinity that synthesizes the moral essence of traditional theology with the scientific rationality of the Enlightenment, thereby completing the second revolutionary transformation in his conception of God and reconstructing a dialectically unified rational theology. This reconstruction of rational theology and the reorientation of the critical philosophy represented both a luminous achievement of Enlightenment reason and the logical starting point for the internalization of faith in modern religious philosophy. It embodied the grand spirit of Kant’s philosophical critique and self-critique, which permeated his entire intellectual project—a testament to the enduring power of reason to interrogate its own limits while forging new horizons for human understanding.

4. The Third Transformation in Kant’s Conception of God: The Construction of Moral Religion in Kant’s Post-Critical Period

While Kant’s critical philosophy achieved the reconstruction of rational theology, it fell short of realizing his ideal of scientific metaphysics, particularly the “Copernican Revolution” in his philosophy of religion. Generally speaking, three unresolved issues remained: (1) Fragmented divinity: Though God’s dual roles were allocated to theoretical and practical reason, the conception remained fundamentally divided: in the theoretical domain, God was reduced to a “merely regulative ideal”; in the practical realm, elevated to a “necessary postulate.” This schism lacked a unifying foundation, fracturing divinity between the epistemic and ethical domains; (2) The irreconcilability between the realm of freedom and the realm of nature renders free will and natural necessity fundamentally incompatible, thereby calling into question the very foundation of morality based on the freedom of the will; (3) Instrumentalized faith: Kant’s practical postulation of God risked reducing religion to a moral instrument—a conditional guarantee for ethical practice—thereby diluting theology’s transcendent dimensions into pragmatic instrumentalization. To resolve these tensions, Kant embarked on a third self-critique, fully subsuming religion under moral architecture and transitioning from rational theology to moral religion. This transformation marked the culmination of his religious-philosophical project, forging a necessary path toward reconciling reason, ethics, and faith.6

Regarding issue (1)—the lack of a unified foundation for God’s fragmented roles in theoretical and practical reason—Kant resolved this issue through a transformation from natural teleology to moral teleology in the Critique of Judgment. In the Critique of Pure Reason, God functions merely as a “regulative concept” guiding the systematization of knowledge without practical efficacy, whereas in the Critique of Practical Reason, God as a “postulate” guaranteeing the summum bonum lacks natural grounding. The Critique of Judgment bridges this divide by demonstrating through “moral teleology” that natural purposes must subordinate their ultimate end to humanity’s moral purpose. This framework elevates God beyond the status of either an epistemological concept or a practical guarantee, unifying Him in the human being as the highest end—a synthesis achieved precisely through reflective judgment’s presentation of natural purposiveness as progressing toward morality. This constitutes the essential distinction of the third Critique’s position from the first two. To elaborate, the fragmentation of God’s functions fundamentally mirrors the inherent duality of human nature: as finite natural beings, humans obey natural laws in the phenomenal realm, while as rational agents, they are bound by moral laws in the noumenal realm. Thus, God in theoretical reason served merely as a regulative principle of nature, while in practical reason, God was a postulate securing the meaning of moral action, with no substantive connection between these roles. Here, God in theoretical reason cannot intervene in human phenomenal activities, while God in practical reason operates only as a regulative ideal for moral conduct—the two remain fundamentally disconnected without the mediating role of teleological judgment. By establishing the moral law as a fact of reason, Kant endowed God with subjective reality. “In Religion Within the Boundaries of Mere Reason, Kant no longer argues for moral theology but systematically expounds its already-demonstrated principles, establishing a rational religion.” (Deng 2008, p. 5). The key to understanding Kant’s moral-theological synthesis lies in the Critique of Judgment. Within the Critique of Judgment, Kant identified three faculties of the human mind: cognition, feeling, and desire. Only the faculty of feeling (embodied in judgment) can mediate between the phenomenal and noumenal dimensions of humanity. Judgment manifests itself as determinative judgment governed by the understanding and reflective judgment which operated in teleology. And reflective judgment was further divided into esthetic judgment which pursues purposiveness without purpose in subjective form and teleological judgment which seeks purposiveness with purpose in objective matter, and interprets nature as a hierarchical system progressing toward ends. Kant unequivocally identified moral humanity—not “natural humanity”—as the ultimate purpose of this system through teleological judgment, Kant interpreted nature as if progressing toward ends. Crucially, he argued that this perspective necessarily leads reason to presuppose moral humanity—not natural humanity—as the ultimate purpose. Only moral agents, endowed with legislative autonomy grounded in freedom, can unify nature and morality. The idea of freedom thus extends across the sensible and intelligible worlds, bridging the realms of nature and morality. with reconciling God’s roles as “legislator of nature” and “legislator of freedom”, and establishing a unified basis for divinity across theoretical and practical domains. Simultaneously, God’s existence as a postulate guaranteed the highest good which is validated through moral teleology. Because moral teleology views the entire external world as a totality aimed at realizing human moral ends, the ultimate goal—the highest good—manifests as the pursuit of virtue in the realm of freedom and the pursuit of happiness in the realm of nature. The coincidence of virtue and happiness, that is, the highest good, thus achieves a harmony between freedom and nature. The realization of the highest good, in turn, retroactively justifies and confers subjective reality upon the existence of God, which reflects Kant’s post-period shift toward the subjectivisation of religion. Here, the human-God relationship underwent an inversion: humanity, as the ultimate purpose of nature and freedom, transformed the question of God’s existence from a theoretical inquiry into the practical necessity of guaranteeing the supersensible grounding of the highest good—the necessary harmony of virtue and happiness as required by moral law. At this point, the God of theoretical reason and the God of practical reason no longer needed to fulfill their respective original roles. The dual existence of the human being within the framework of moral teleology assumed those functions. As a finite natural being, the human subject organizes systematic knowledge of nature through cognition, thereby exercising the regulative role. As a finite rational being, the human subject realizes freedom through moral action, embodying the ultimate end itself and thereby fulfilling the function of a postulate. In this way, God’s dual functions found their unification in the moral subject, once again highlighting humanity’s sovereign role in “legislating for nature.” As Paul Guyer observed in Kant and the Experience of Freedom: Essays on Aesthetics and Morality, the concept of God in Kant’s critical philosophy is not a metaphysical absolute but a practical necessity, whose significance revolves around human moral needs—this is the core of his “anthropocentric teleology” (see Guyer 1993, pp. 304–35).

Regarding issue (2), The opposition between the realm of freedom and the realm of nature likewise finds its reconciliation in the human being conceived as an end. This tension originated from Kant’s epistemic distinction between objects as appearances (phenomena) and things as they are in themselves (noumena)—a distinction of perspectives, not segregated realities. Crucially, this framework necessitates mediation not because the realms are disconnected, but because finite rational beings must operate across both perspectives: (1) As natural beings bound by causal laws (phenomenal); (2) As free agents bound by moral law (noumenal). Kant’s resolution centered on humanity’s unique capacity for practical self-determination, which bridges the perspectives through moral action. As previously established, finite rational beings manifest itself by dual identities: (1) In the phenomenal realm, humans are natural beings governed by natural causality; (2) In the noumenal realm, they are free beings bound by moral law. In the Critique of Judgment, Kant posited teleological judgment—a mode of reflective judgment—as the mediating link between freedom and necessity. Humanity legislated unconditionally over nature without being subordinated to any higher purpose, for as the ultimate end, humans cannot exist for the sake of anything else (including God). The highest end, by definition, cannot itself have a further purpose. The dual-natured humanity, while subject to natural laws in the phenomenal realm, simultaneously orients those laws toward moral ends. As both thing-in-itself (noumenon) and empirical being (phenomenon), humans transcend heteronomy imposed by external conditions, achieving autonomy through self-legislated moral will. Human autonomy becomes the very source of moral law, with rejecting all instrumentalization or objectification of human value. Consequently, the natural order necessarily serves moral ends, and natural causality transforms into the enabling condition for moral freedom. Therefore, the establishment of a moral-religious system centered on the human being marks the construction of a bridge between freedom and necessity, thereby dissolving their mechanistic opposition. Yet, this “unity” is not to be understood as the “dual-aspect fusion” advocated in the Groundwork of the Metaphysics of Morals—a position Kant explicitly abandoned in the Critique of Practical Reason in favor of the “fact of reason.” Moreover, any ontological fusion of noumenon and phenomenon within the moral subject would violate Kant’s fundamental epistemological commitments. The unity Kant achieves here is realized through the praxis of the moral subject: in the Critique of Judgment, the duality of the moral agent is integrated through a purposive-reflective standpoint, wherein natural necessity and moral freedom become congruent in meaning. This is a regulative—not ontological—unity, and it constitutes a significant advance beyond earlier theoretical attempts at reconciliation. It should be noted that although Kant demonstrates a “compatibilist” inclination throughout the Critique of Pure Reason and indeed his entire philosophical system, there exist substantive distinctions within his compatibilist views across different periods. In the first Critique, Kantian compatibilism manifests as treating the noumenal and phenomenal as two modes of cognition regarding the same object, thereby constructing a bridge between theoretical and practical reason, nature and freedom. Nevertheless, it fails to demonstrate how freedom can manifest within the natural order, remaining merely an abstract logical possibility. By contrast, in the third Critique, through the mediating function of teleological justification, Kant arrives at the actualization mechanism for realizing freedom: (1) At the individual level: Moral disposition shapes the empirical world—transforming phenomenal actions into moral acts through intentionality. As when the demand for honesty manifests as causality in the phenomenal realm, yet constitutes a moral imperative in the noumenal realm; (2) At the historical level: Civilizational progress serves as the vehicle for moral advancement, wherein humanity’s ethical development embodies natural purposiveness evolving toward moral ends.

Having beheaded Deism, Kant not only demolished the foundations of theological metaphysics and negated all epistemological possibilities of knowing God, but also reduced divinity in the practical realm to a mere “postulate” ensuring the realizability of human morality. One might argue that he abolished religion’s transcendence over philosophy and faith’s primacy over reason. God, in this framework, serves as both a “servant” to rational demands and a logical supplement to moral law. In 1799, Friedrich Schleiermacher sharply criticized this approach in his On Religion: Speeches to Its Cultured Despisers, accusing Kant of subordinating religion to morality and eroding its autonomy, arguing that Kant merely defended moral law’s independence while collapsing religious distinctiveness. He explicitly stated: “Were it the case, morality and genius apart would be only fragments of the ruins of religion, or its corpse when it is dead. Religion was then higher than both, the true divine life itself.” (Schleiermacher 1958, p. 29) Yet, Kant never intended to instrumentalize theology nor deny religion’s transcendent dimension. Rather, he internalized faith within human moral law through the subjectivisation and moralization of religion, constructing a firmer foundation for belief than traditional theology could offer. In his rational theology, Kant dismantled speculative theology, replacing it with moral theology of modern significance. Here, God ceases to be an object of knowledge—cognizable through sensibility or understanding—and becomes a moral necessity of practical reason, subjective yet inescapable. Traditional theological approaches to God, Kant argued, inevitably lead to mysticism or skepticism, whereas moral religion, by answering the question “Was ist der Mensch?” affirms God’s existence through the anthropological turn in theology. By grounding theology in morality—transitioning from religious morality to moral religion—Kant inverted the relationship between ethics and faith without diminishing divine sanctity. His theological “Copernican Revolution” reoriented the human-divine dynamic, offering Enlightenment thinkers a novel framework to reconcile faith with reason. Though Kant stated in Die Religion Innerhalb der Grenzen der bloβen Vernunft (hereafter Religion): “Die Moral bedarf also zum Behuf ihrer selbst (sowohl objektiv, was das Wollen, als subjektiv, was das Königen angeht) keiner Religion, sondern vermöge der reinen praktischen Vernunft ist sie sich selbst genug.” (Thus morality in no way needs religion (whether objectively, with respect to willing, or subjectively, with respect to ability) for its own sake; by virtue of pure practical reason, morality is self-sufficient.) (Kant 1914, AA 6, p. 3) (Religion within the Bounds of Bare Reason), he simultaneously asserted that morality inevitably led to religion: “Der rechte Weg ist nicht von der Gnade zur Tugend, sondern von der Tugend zur Gnade.” (The right way is from virtue to grace, not from grace to virtue.) (Kant 1914, AA 6, p. 47) (Religion within the Bounds of Bare Reason). For Kant, morality suffices as an end in itself, requiring no divine grounding, yet it perpetually directs humanity toward God. This reconfiguration secures a sanctuary for divinity within the moral world anchored solely in the moral conscience. “When confronted with their moral conscience, people find God’s existence necessary—a bridge from earthly ethics to transcendent felicity, a necessary demand (though not ground) of moral duty” (Zhao 2012, p. 30). Crucially, while affirming the transcendence of God or religion, Kant systematically explicates the relationship between ends and means in the Critique of Judgment to avoid instrumentalizing faith. Here, he emphasizes treating humanity as an end in itself while simultaneously recognizing morality as its own ultimate end. Within this teleological framework, God is not an instrumental guarantee for aligning virtue with happiness, but rather the a priori necessary condition that makes the summum bonum possible. God’s status and function remain indispensable in this system, while moral action as an end in itself inherently incorporates faith as constitutive of autonomy—both ultimately converge on the necessity of treating faith itself as an end. Finally, in Religion within the Boundaries of Mere Reason, Kant dedicates extensive critique to institutionalized religion’s “counterfeit service”, exposing it as fetishism, while defining the “true service” of God solely as fulfilling moral duties and embracing a virtuous way of life—with no other prerequisites. We may conclude that the religion, faith, and theology Kant champions derive their piety precisely from this practical significance. By rejecting the external forms of faith—dogma and ritual—Kant affirms its intrinsic transcendence. Although the highest end of teleological judgment is humanity itself and its freedom (not God), God as the holy moral legislator is presupposed in this reflection as the existential meaning of moral autonomy. It must be emphasized that when faith’s transcendence no longer depends on God’s external authority or requires revelation for its recognition, but instead originates from the sublime moral law, it truly transcends individual experience and contingency. Internalized as the necessity of moral law, it achieves a far more profound foundation than traditional theology—a testament to religion as the consummation of practical reason.

The completion of Kant’s self-critique of rational theology marks the third revolutionary transformation in his conception of God—the establishment of a moral-religious system that consummates his project of scientific metaphysics. The essence of Kant’s moral religion is not merely theological but anthropological: without religion’s spiritual dimension, anthropology lacks transcendence; without anthropological praxis, religion forfeits actuality. Moral religion stands as both the pinnacle of Kant’s critical philosophical system and the highest achievement of Enlightenment rationality. It negated traditional religious authority while preserving space for faith, critically mediating the tensions between reason and faith, morality and religion, freedom and grace. Through relentless self-limitation and critique, it liberated metaphysics from its servile role as “the handmaid of theology,” redefining God not as an object of knowledge but as a guarantee for moral fulfillment, and religion not as a collection of dogmas but as an expression of reason. While Kant’s philosophy may leave unresolved questions for posterity, moral religion represents his definitive answer to the core task of his philosophical project—a synthesis of incalculable systematic value. Yet, the interplay between the conception of God and the question “Was ist der Mensch?” continued to inspire thinkers who follow in his footsteps to probe the essence of the divine–human relationship, inaugurating modernity’s secularization and emotionalization of religion. In this way, Kant’s moral religion not only concluded his critical journey but also opened new horizons for reimagining faith in a post-metaphysical age.

5. The Intrinsic Internal Roots Underlying Kant’s Three Pivotal Transformations in His Conception of God

A comprehensive examination of Kant’s three pivotal transformations in the conception of God reveals his philosophy not as a fragmented patchwork of contradictions but as a coherent, self-correcting system. Just as Henry Allison observes in Kant’s Transcendental Idealism, Kant’s critical philosophy is a dynamic process of self-correction, and the transformation of the concept of God exemplifies this methodological consistency (see Allison 1983, pp. 405–10). While these transformations appear externally as responses to internal systemic contradictions through critique and self-critique, their driving force must be sought not externally but within the philosophical architecture itself. The logical necessity (rather than historical) of these transformations arises from four internal roots that collectively propel the logical evolution of Kant’s philosophy of religion: (1) Methodological Foundation: The Development of Critical Philosophy; (2) Systematic Goal: The Establishment of Scientific Metaphysics; (3) Axiological Orientation: The Secularization of Theology into Anthropological Theology; (4) Practical Culmination: The Extension of Pure Moral Philosophy. These four dimensions—methodological, teleological, axiological, and practical—operate synergistically to drive both the systematic construction of Kant’s philosophy of religion and the logical progression of his conception of God.

(1)

Methodological Foundation: The Development of Critical Philosophy: The evolution of Kant’s critical-philosophical method constitutes the methodological cornerstone for the transformations in his conception of God. At the core of critical philosophy lies the determination of knowledge’s limits through “critique of reason”, a method Kant rigorously applied across epistemology, ontology, teleology, and moral philosophy to drive three pivotal transformations of his conception of God. Specifically, in the pre-critical period, Kant initially employed this method to revise dogmatism within the Leibniz-Wolff System for rejecting traditional cosmological and teleological proofs of God’s existence. In the period of the critical philosophy, by launching the “Copernican Revolution” in epistemology, Kant radically overturned methodological assumptions with expelling the question about God entirely from the cognitive domain and invalidating all a priori demonstrations of divine existence. Yet, Kant preserved God’s status as a “pure ideal” of practical reason, laying the groundwork for subsequent transformations. And in the post-critical period, by extending the critical method to teleology and ethics, Kant expanded the question about God from the epistemic to the practical realm, with achieving a unified critical framework spanning epistemology and moral philosophy.

(2)

Systematic Goal: The Establishment of Scientific Metaphysics: Kant’s philosophical ambition extended beyond critiquing traditional dogmatic metaphysics to establishing a new scientific metaphysics. His reform of traditional metaphysics fundamentally aimed to reconstruct theology from the “pinnacle of special metaphysics” into a “practical component of scientific metaphysics.” In the Wolffian system, God as the “most perfect being” constituted the apex of ontology. Kant thus subsumed theology within the framework of rational critique, with liberating metaphysics from its subservient role as “theology’s handmaid” and transforming God into a “postulate of moral teleology”—a nexus connecting nature and freedom. Kant recognized that traditional theology’s fundamental error lay in situating the conception of God within the cognitive domain. Consequently, through methodological evolution, he relocated the God-concept to the practical realm, redefining it from an “object of knowledge” to a “practical postulate”. This transformation allowed him to (a) transcend traditional theological paradigms; (b) evade skeptical critiques; (c) respond to deistic challenges; and (d) ultimately lay the foundation for scientific metaphysics—precisely the goal set for moral religion. As Paul Guyer stated in Kant and the Claims of Knowledge, Kant’s aim was to transform theology from a dogmatic authority into a rational faith, making it a component of scientific metaphysics (see Guyer 1987, pp. 19–20).

(3)

Axiological Orientation: The Secularization of Theology into Anthropological Theology: Kant consistently framed his philosophical inquiries around four questions: “Was kann ich wissen? Was soll ich tun? Was darf ich hoffen? Was ist der Mensch?” (Kant 1922, AA 11, p. 429). The answer to the first three questions, he asserted, are footnotes to the fourth—“Was ist der Mensch?”—a query that permeated Kant’s entire philosophy, underscoring its intrinsic anthropological imperative. Dissatisfied with the external antagonism between theology and anthropology, Kant sought to internalize theological questions within an anthropological framework, fundamentally reconstructing theology’s discursive system. This reconstruction stems from Kant’s profound insight into humanity’s dual nature as both “finite natural beings” (subject to natural causality) and “finite rational beings” (moral agents). Human reason, as a cognitive faculty, is limited—incapable of knowing God’s noumenal existence through theoretical reason. Yet, as moral subjects, humans necessarily strive to transcend natural determinism, pursuing the highest good (summum bonum) as their ultimate end. This tension extends to God as the absolute infinite being, transforming into the problem of how finite beings may aspire to the infinite. To resolve this, Kant argued for the necessity of positing God as a moral postulate. As Heine jokingly stated in his Zur Geschichte der Religion und Philosophie in Deutschland, after driving God out the front door through theoretical critique, Kant welcomed Him back through the back door as a moral necessity (see Heine 1955, pp. 70–71). Yet, these two “Gods” are fundamentally distinct: the expelled deity is the ontological God (an absolute being), while the reintroduced one is the moral God—a “pure ideal” devoid of theoretical cognition but indispensable to practical reason. This inversion reconfigured the divine-human relationship for completing theology’s anthropological transformation. “In Kant’s philosophy, all questions ultimately relate to the human condition in varying forms and perspectives, with becoming facets of anthropological inquiry.” (Xie 1997, p. 24).

(4)

Practical Culmination: The Extension of Pure Moral Philosophy: Kant’s moral philosophy centers on “pure practical reason”—a form of reason that expresses itself through a universally and necessarily valid moral law, functioning via moral autonomy and requiring the direct identity of the will with the law in practical action. Kant recognized that this universally binding moral law encounters a fundamental difficulty in practice: as finite natural beings, humans struggle to fulfill the moral demand for the highest good (summum bonum), understood as the unity of virtue and happiness, within the empirical world. In order to maintain the internal consistency of practical reason, Kant introduces the postulates of “God’s existence” and “the immortality of the soul” as necessary assumptions of reason, designed to prevent moral purposiveness from lapsing into utopian speculation. These postulates are not grounded in any inevitable moral progress in time, but rather serve as purposive constructs aimed at preserving the universal validity of the moral law. This formulation ensures that rational moral agents do not lose their commitment to moral obligation in the face of injustice or unrealized ideals, thereby safeguarding the motivational and binding force of the “ought” within reason itself. So, as Kant points out in the Religion, the moral-religious system does not require the existence of God. Yet, morality necessarily extends into the religious domain through the internalization of faith—a faith that emerges precisely from the aim inherent in morality itself. This moral aim inevitably requires positing the existence of God as the logical condition for the possibility of the highest good. Accordingly, religion in Kant’s system no longer serves as the foundation of morality but becomes a necessary faith-form generated from within pure morality. In this final synthesis, Kant transforms religion from an external metaphysical framework into an internal moral structure: it is not faith that gives rise to morality, but the moral idea that intrinsically points toward a religious form. Faith, in this sense, becomes the rational extension of pure practical reason, marking the final integration of Kant’s philosophy of religion.

In summary, these four motivations—progressively layered—necessitated the three pivotal transformations in Kant’s conception of God. The methodological evolution demanded by the system of the critical philosophy provided instrumental safeguards for establishing scientific metaphysics, while the foundation of scientific metaphysics set the agenda for Kant’s philosophy of religion, with compelling him to scrutinize theology within the framework of reason. Simultaneously, the anthropological axiological orientation inherent in Kant’s human-centric philosophy led to the secularization of theology into anthropology of both the conception of God and theology itself. Finally, through the logical culmination of pure morality, faith was fully internalized, coalescing into an internally unified and distinctive moral-religious system that inaugurated a new epoch of Christian faith. This deep mutual corroboration reveals that the tension between reason and faith in Kant’s philosophy of religion is not an inherent flaw but a manifestation of its systemic dynamism.

6. Conclusions

Generally speaking, Kant’s critical process of critique and self-critique—centered on the conception of God and addressing the fundamental tension between reason and faith as manifested differently across his philosophical periods—culminated in three revolutionary transformations in his conception of God. (1) First transformation (in Kant’s pre-critical period): deconstruction of traditional theology. Marked by the critique of traditional theological-metaphysical proofs for God’s existence in the Evidence, Kant proposed a novel ontological proof based on “conditions of possibility”, rejecting dogmatic logical deduction while mediating the conflict between personal theism and pantheism through deistic arguments. Yet, God’s image remained fragmented in Kant’s system, necessitating further critique. (2) Second transformation (in the period of the system of Kant’s critical philosophy): reconstruction of rational theology. Marking the boundary of reason through the epistemological “Copernican Revolution” launched by his critical philosophy, Kant denied the possibility of knowing God through epistemic means and transferred the idea of God into the domain of moral practice. In doing so, he curtailed the potential escalation of conflict between reason and faith over the issue of God. However, this suppression of contradictions did not resolve them but merely concealed their persistence. (3) Third transformation (in Kant’s post-critical period): construction of moral religion. Only in this final phase did Kant fully reconcile the reason–faith antagonism within his conception of God. Through the anthropological turn, Kant unified God’s disparate aspects under the principle of “humanity as an end”. Whether as divine legislator, benevolent ruler, or just judge, God ceased to wield transcendent authority, becoming instead the subjectivized universal law of moral autonomy—a sanctuary for divinity within human ethical practice. Having completed these transformations, Kant reconfigured God from a cosmic sovereign or natural legislator into a guarantee for moral fulfillment and a necessary condition for morality. Dogmatic authority and religious sanctity were transfigured into rational faith and moral transcendence, for securing an irreducible place for God amid the Enlightenment’s rationalist currents.

To further deepen the present study’s account of the evolution of Kant’s conception of God, it is necessary to include his late, major manuscript, Opus Postumum, within the scope of discussion. The main trajectory of this paper is to trace the development of Kant’s religious philosophy through the transformation of his concept of God across distinct periods. Accordingly, the tripartite division employed here—pre-critical, critical, and post-critical—follows the dominant methodological phases of Kant’s critical philosophy. Opus Postumum, strictly speaking, does not fully conform to this periodization. Its philosophical method and aims arguably transcend even the post-critical agenda that Kant sought to complete. Nonetheless, as Michael Forster has emphasized in Kant’s Final Synthesis: An Essay on the Opus Postumum, this work represents Kant’s final attempt at a “synthesis” of his system—a structural integration of the theoretical, practical, and aesthetic architectures laid out in the Critique of Pure Reason, Critique of Practical Reason, and Critique of the Power of Judgment (Forster 2000). For this reason, the Opus Postumum constitutes a significant extension of the theoretical horizon of this study and cannot be overlooked.

In Opus Postumum, Kant famously declares: “Das Ich setzet sich selbst, aber es ist auch das Subjekt aller Realität” (The I posit itself, but it is also the subject of all reality.) (Kant 1936–1942, AA 21, p. 15) (Opus Postumum)—“Then I posit itself and is also the subject of all reality.” This proposition signals a novel understanding of the self in Kant’s late philosophy: no longer merely the analytic ground of pure reason, the self becomes the active integrator of nature and freedom. This shift directly engages key theses in this study—such as the human subject’s role in “legislating for nature” and the regulative function of morality. In this manuscript, Kant reconfigures the relationship between God, the postulates, and practical reason. God is no longer treated simply as a hypothetical postulate invoked by practical reason for the realization of the highest good (as in the Critique of Practical Reason) but is increasingly understood as a conceptual precondition for the unity of the system as a whole. This transformation does not entail a return to metaphysical theology in the traditional sense. Rather, Kant—while adhering to the boundaries of reason—constructs a triadic structure of “humanity–nature–morality” that gives critical philosophy its highest architectonic unity. For example, Kant writes that “Die Natur wird als ein System gedacht, nicht bloß nach mechanischen Gesetzen, sondern auch als ein zweckmäßiges Ganzes, das durch Freiheit in einem moralischen Sinne möglich gemacht wird.” (Nature is conceived as a system, not merely according to mechanical laws, but also as a purposive whole made possible by freedom in a moral sense.) (Kant 1936–1942, AA 21, pp. 27–35) (Opus Postumum), thus departing from the earlier view of nature as a merely mechanistic system and reconfiguring it as the domain of moral realization. This notion is closely aligned with this paper’s argument concerning the bidirectional structural support between knowledge and morality afforded by regulative principles. Similarly, Kant insists that “Die systematische Einheit der Natur ist keine Erfahrungstatsache, sondern eine Forderung der Vernunft.” (The systematic unity of nature is not a fact of experience, but a demand of reason.) (Kant 1936–1942, AA 21, pp. 28–29) (Opus Postumum), reaffirming the essential function of ideas such as God, the postulates, and purposiveness—not as objects of knowledge, but as necessary conditions for systematic completeness within the Kantian framework. Forster’s methodological interpretation of the Opus Postumum substantially complements this paper’s approach. He maintains that Kant, in this final work, moves beyond relegating God and the soul to the domain of the unknowable, and instead articulates a project of “rational self-integration”—a transformation of rational faith into an internal structure through moral praxis. This integrative strategy of the post-critical period directly addresses longstanding criticisms regarding internal tensions in Kant’s system. It not only provides a philosophical foundation for the ultimate destination of Kant’s concept of God but also substantiates the thesis that “God, exiled from the realm of knowledge,” ultimately finds a legitimate home within moral practice.

On the whole, the profundity of Kant’s three pivotal transformations in the conception of God lies not only in their systemic significance for his philosophy but also in their resolution of modern religion’s fundamental dilemma: how to preserve a space for faith’s transcendence in an increasingly rationalized world while grounding sanctity within an ever-secularizing religious landscape. Kant’s answer is two-folds: (1) God ceases to be the starting point of faith and becomes the necessary presupposition of morality—a condition for humanity’s moral perfection; and (2) religion no longer serves as the guarantor of ethics but emerges as the institutionalized expression of rational praxis. In this sense, we may regard Kant’s moral religion as the paradigmatic culmination of Enlightenment rationality, while his conception of religion fundamentally constitutes an anthropological turn in political philosophy (see Fu 2015, pp. 247–69). The three pivotal transformations in Kant’s philosophy of religion—achieved through relentless critique and self-critique—represent the apex of the Enlightenment and the ultimate manifestation of his dialectical spirit. Nevertheless, Kant’s solutions are imperfect; they inaugurated new problematics and methodologies for modern philosophy and Christian faith. Traditional theology’s foundations were dismantled, yet the internalization of faith bequeathed an intellectual legacy for later theologians like Schleiermacher to reexamine faith’s legitimacy and humanity’s profound existential needs—a legacy that continues, like a torch, to guide thinkers navigating the interplay of reason and faith. Just as Kant said in the Critique of Practical Reason: “Zwei Dinge erfüllen das Gemüt mit immer neuer und zunehmender Bewunderung und Ehrfurcht, je öfter und anhaltender sich das Nachdenken damit beschäftigt: Der bestirnte Himmel über mir, und das moralische Gesetz in mir.” (Two things fill the mind with ever new and increasing admiration and awe, the more often and steadily we reflect upon them: the starry heavens above me and the moral law within me.) (Kant 1913, AA 5, p. 161) (Critique of Practical Reason). In a disenchanted world where the conception of God fluctuates between eclipse and resurgence, the challenge of embracing sanctity under reason’s illumination has become a quintessential modern existential quandary. Kant’s response resounds: sanctity resides not in a transcendent God but in immanent humanity. This, perhaps, is his profoundest philosophical insight: true Enlightenment rationality does not negate or expel the sacred, nor does it replace divinity with humanity. Rather, it seeks meaning through critique and self-critique, witnessing the sublime in the very act of moral self-legislation.