The subject of Insole’s immensely rich and well-researched book is Kant’s concept of the highest good. It serves the author as a fitting pretext for a fresh treatment of an encyclopedic range of topics, including freedom, morality, happiness and God, as they are developed by Kant from the pre-critical period of the 1760s–1770s to the mature critical period of the 1780s–1790s. The book challenges our understanding of both Kant’s ethics and his religious philosophy. Insole’s religious-philosophical approach to Kant’s ethics is unparalleled in the extent to which it takes seriously its metaphysical commitments. The result is an in-depth and sustained investigation of two concepts whose nature and systematic function have not yet been well understood in the literature, namely, the proper self and the moral world. Insole’s unique appreciation of what Kant’s radical conception of freedom as autonomy entails for his philosophical theology leads him to portray Kant as making a cleaner break with the Christian Pietist tradition than most interpreters are ready to admit. In taking Kant to be ‘philosophically committed to a conception of God’ (p. 156), Insole does not see him as trying and failing to be an orthodox Christian believer; far from it, he has no qualms in placing Kant squarely in the Shaftesburyan tradition of humanistic deism, counting him among those who venture to defend meaning and human values by means of some pagan, rationalist form of anti- or supra-naturalism.

Most generally, the book can be divided into a negative and a positive segment. The negative segment (the first five chapters) provides an account of Kant’s conception of the highest good in the 1750s–1760s, as it was passed down from the classical (Aquinian, Lutheran and Leibnizian) theological traditions, and considers the extent to which this conception began to be upended from the late 1760s onwards as a result of Kant’s dawning conviction that freedom requires autonomy. If we are to be free, our will must be by and for itself and not have God for either its unconditionally first cause or its unconditionally good object. If the will is to be unconditionally good, nothing else, not even God, can be unconditionally good at the same time.

Against this background, the positive segment (the remaining thirteen chapters) delivers a new interpretation of Kant’s ethics and religious philosophy. Insole explains its novelty in terms of what he calls ‘Kant’s non-Christian philosophical religiosity’ (p. 1). By this, he means ‘a religiosity grounded in what reason itself can bring us to, in relation to wisdom and the divine, without reliance upon revelation or Scripture’ (p. 156). It relates to a ‘transcendent dimension’ that finds expression in four areas of Kant’s critical system: transcendental idealism, the proper self, the moral world and the moral proof of God’s existence. As Insole sees it, freedom is the centre-point of the entire system. Granted that the natural mechanism of spatiotemporal objects threatens freedom, ‘if reality were spatial and temporal all the way down … then there would be no dimension of reality wherein freedom could be found’ (p. 158). If freedom is possible, there must be a dimension of reality ‘beyond, and prior to, space and time’ with which ‘the fate of morality is closely bound up’ (p. 230). Among the things we might think of as populating this transcendent dimension, we are, insofar as we are obligated by the moral law, warranted to think of a ‘proper self’ of ours, i.e. a self ‘conceived of outside of space and time, in its noumenal, transcendental freedom’ (p. 163), and think of it as inhabiting, or hoping to inhabit, a ‘moral world’, i.e. an ideal moral community where everyone acts as s/he is obligated by the moral law.

As God can no longer be our efficient and final cause, He is banished as it were to the outskirts of the Kantian scheme of things. Nevertheless, through the moral argument for God’s existence, God retains His role as guarantor of the proportionate distribution of happiness in accordance with morality. One of the more curious features of Insole’s interpretation is this: in setting out to show that the argument is ‘a far more holistic, powerful, and central element of Kant’s notion of freedom and autonomy than is often realized’ (p. 156), it ends up rendering God superfluous. At the heart of the interpretation is the thesis that ‘belief in freedom, and in a noumenal intelligible realm, is a crucial step towards, indeed the lynchpin of, Kant’s philosophical-religious hope’ (p. 264). Since upon believing in freedom, we affirm in thought (as opposed to cognition or knowledge) a proper self who lives, or hopes to live, in an ideal moral community or world in which the highest good is possible, it follows that to ‘conceive of a universe wherein it is possible to follow the moral law, is already to conceive of a universe wherein the harmony of purposive patterns of end-setting is the intrinsic goal, in that, if the project of universal end-setting were to unfold without hindrance, we would have a perfect and complete moral community’ (p. 237). Far from being a gratuitous ‘add-on’ to Kant’s ethical system, the moral argument is, Insole argues, very much an integral part of the system. But if the moral world is ‘so structured, that we could hope that being moral will be met with proportionate happiness’ (p. 322), it is hard see to what else is left for God to do. In a move remarkably reminiscent of the ‘atheism dispute’ of the late 1790s, Insole claims that God’s role as guarantor of the proportionate distribution of happiness in accordance with morality should collapse into that of ‘a sort of conceptual place-holder, for the stability of the moral world’ (p. 323).

To be clear, Insole is not contending that Kant holds the latter view of God’s role, but that he should, especially given his principle of methodological parsimony, have held it. Insole’s core thesis is that belief in freedom is the lynchpin of our religious hopes, the belief from which every other belief follows. He makes his case by drawing attention to the unduly neglected fact that belief in a moral world goes hand-in-hand with belief in freedom and unpacking what belief in the moral world implies for the highest good. Since (belief in) the moral world amounts to (belief in) a world in which the highest good is possible, (belief in) freedom already encompasses (belief in) the highest good’s possibility. The latter is no less a part of Kant’s ethical system than the former. And since the moral world is a world in which happiness follows necessarily from morality, Insole concludes that God is rendered redundant in His role as guarantor of the proportionate distribution of happiness in accordance with morality in it.

The natural worry for this line of argument is that (belief in) freedom is made to do too much work. We might grant Insole that, upon believing in freedom, we believe in a moral world of which our proper self is a part; we might also grant him that the moral world is a world in which the highest good is possible. My question is whether the concept of a moral world of which our proper self is a part eo ipso entails that of a world in which the highest good is possible, so that we cannot think the former without thinking the latter. It is not clear, to say the least, that the concept of the moral world does not undergo development in the course of its exposition. In chapter 11, Insole explains how, in the second Critique, the moral world is deduced from the practical antinomy in the Dialectic of Practical Reason, where the argument involves considerations of how morality and happiness are combined in the highest good. But the moral world is first introduced in the Analytic of Practical Reason with no such consideration. Instead, it is introduced there in terms of our ‘existence as determinable in an intelligible order of things’ (AA, 5: 42) – a clear allusion to our proper self. Here we seem to have an instance of the concept of a moral world of which our proper self is a part that does not eo ipso entail that of a world in which the highest good is possible.

The same worry can be raised from a different angle, in terms of how morality and happiness are combined in the highest good. In chapter 13, Insole argues that the happiness that goes into making up the highest good is nothing over and above the happiness that ensues upon the moral perfection we are to expect of every member of the moral world. This lays the groundwork for Insole’s argument in chapter 16 that God’s role as guarantor of the proportionate distribution of happiness in accordance with morality is reducible to that of a place-holder for the moral world’s stability. His overarching argument is that since, inasmuch as we believe in freedom, we already believe ourselves to be a member of the moral community in which happiness is (or will be) distributed in accordance with morality, there is no need for us to further believe in God’s existence in order for us to believe in the highest good’s possibility. To show that membership in the moral community already guarantees happiness, Insole employs a battery of Kant’s Reflections from the 1760/1770s that putatively assert that morality of itself gives rise to happiness (see p. 267). In doing so, he is not, he stresses, arguing that Kant identifies morality with happiness. As he recognizes, Kant is clear that morality and happiness are two distinct components of the highest good – happiness, for instance, is something more than Stoic moral contentment. Nevertheless, Insole claims, Kant sees morality as the ground (or cause) of happiness in the sense of being a sufficient condition for it. However, given the distinctness of morality and happiness, there is, as far as I can see, nothing unthinkable or inconceivable about a system of actions that coordinate, support and harmonize with each other in a way that is in accordance with morality without coordinating, supporting and harmonizing with each other in a way that guarantees the proportionate distribution of happiness in accordance with morality.

In support of his claim that morality of itself suffices for happiness in the moral world, Insole cites the Canon of Pure Reason, where Kant writes that ‘such a system of happiness proportionately combined with morality can also be thought as necessary, since freedom partly moved and partly restricted by moral laws, would itself be the cause of the general happiness, and rational beings, under the guidance of such principles, would themselves be the authors of their own enduring welfare and at the same time that of others’ (A809/B837). However, Kant might be read here as expounding the moral world in two steps: first, morality presupposes ‘a special kind of systematic unity, namely, the moral’ (A807/B835); second, this moral systematic unity ‘can also be thought’ as a ‘system of self-rewarding morality’ (A809/B837). Read in this way, the concept of a moral world inferred in the first step does not entail that of a proportionate combination of happiness with morality introduced in the second step. Such a reading aligns more neatly with the separation Kant wants to maintain between acknowledgement of the moral law’s validity and affirmation of the highest good’s possibility and God’s existence. As he writes, the moral argument

Back in the Canon, Kant adds shortly after the quoted passage that ‘the necessary connection of the hope of being happy with the unremitting effect to make oneself worthy of happiness that has been adduced … may be hoped for only if it is at the same time grounded in a highest reason’ (A810/B838). Read in this larger context, the claim that morality suffices for happiness in the moral world turns out to be based upon an unspoken assumption of divine mediation.

Insole’s point that God’s role as guarantor of the proportionate distribution of happiness in accordance with morality is more poignantly couched in terms of a place-holder for the stability of the moral world is well-taken. But in view of the distinctness of this sense of the moral world from the sense of the moral world that is presupposed by freedom, the moral argument’s conclusion is not as trivial as Insole would have it. In other words, (belief in) the highest good’s possibility follows from (belief in) freedom and a moral world not immediately – but (belief in) some unknown being guarantees the proportionate distribution of happiness in accordance with morality in the moral world.