In order to be able to pass an accurate judgement on this new product of the Kantian genius—which is more than a mere reworking of the Groundwork of the Metaphysics of Morals—and on its relation to the doctrines of other philosophers, it is necessary to uncover the main principles on which the author builds, and by means of which he proceeds, and to accompany them individually with comments. In order to make the occasionally necessary reference to them easier, I will number them.

Johann Friedrich Flatt (1759–1821) was a lecturer in theoretical philosophy in Tübingen from 1785–1791. As the resident Kant expert, during this time Flatt was responsible for reviewing both pro- and anti-Kantian works in the local academic journal, the Tübingische gelehrte Anzeigen. Flatt also reviewed Kant’s works themselves, including the Groundwork, translated into English in this chapter for the first time. The main theme of the review is Kant’s inconsistency, but Flatt also makes a claim that is repeated by other early critics, such as Tittel and Pistorius, namely that Kant’s own examples reveal that the categorical imperative cannot determine concrete duties without referring to experience, despite what Kant might say to the contrary. We have good reason to believe that Kant read Flatt’s review of the Groundwork, and Kant likely has Flatt in mind at 5:4.28–37n and 5:5.24–6.11 when discussing various alleged inconsistencies in his writings.

What thelematology is. Before I turn to the guide to living rationally itself, it is necessary that I issue the doctrine of the human will as preparation in advance, without which one cannot possibly succeed in the following. For, since the guide to a rational life includes solely those rules that are prescribed to the will, and which must therefore be derived, for the most part, from the constitution of the will, it is easy to see that one must first know how the will is constituted and works by nature before one can sufficiently explain how it ought to be. One can justifiably call this doctrine thelematology or the doctrine of the will, a name by which I mean nothing other than a theoretical science of the properties, powers, and effects of the human will. The idea is therefore that we here seek out, as far as possible, the causes [4] of that which we perceive in the will through experience with the intention of learning to both better recognize and judge good and evil as well as promote the former and eradicate and hinder the latter. Why it is treated here. I believe that this is the correct place to treat this important subject. It is indeed known that many tend to include it in metaphysics. It seems to me, however, that this is not done correctly, in that metaphysics must without a doubt lose all determinate boundaries if one is also permitted to treat contingent truths in it, concerning which one has no assurance that they cannot be otherwise in a different world, and which one cannot know a priori on the basis of the necessary essence of a thing or of a world in general. Nonetheless, one can simply grant each scholar their own freedom on this matter.

Christian Wolff (1679–1754) was a profoundly important philosopher during the eighteenth century. ‘Wolffianism,’ broadly defined as adherence to Wolff’s teachings, was taught and promoted at all the major German universities for decades. Kant was educated and began his career within an environment that was dominated by discussion between proponents of and opponents to Wolff’s philosophy. This chapter contains a complete translation of Chapter 1 of Part 1 of Wolff’s ‘German Ethics’ (1720), in which Wolff gives a general overview of almost all the core features of his ‘universal practical philosophy.’ The translation contained in this chapter therefore serves as a concise introduction to Wolff’s ethics in general, and one that is especially helpful for better understanding Kant’s explicit reference to Wolff’s principle of perfection in the second Critique (see 5:40), among other things.

In this work the author further elaborates on the ideas, to which he had given an introduction in his Groundwork of the Metaphysics of Morals, and which at the same time can serve as a brief outline of his doctrine of morals, insofar as he here thoroughly deals with the following questions: whether and in what way pure reason is practical, whether it has any relation to the faculty of desire, what kind of relation this is, and how we can conceive of the relation as possible and actual.

One of the most significant philosophical events during the final decades of the eighteenth century was the so-called ‘pantheism controversy.’ An important event during the controversy was the initially anonymous publication of Thomas Wizenmann’s 1786 book entitled The Results of the Jacobian and Mendelssohnian Philosophy, Critically Examined by A Neutral Party. Kant responds to this book in his essay ‘What does it mean to orient oneself in thinking?’. This chapter contains a complete translation of Wizenmann’s subsequent response to the ‘Orientation’ essay, written in the form of an open letter to Kant. The most important claim of the letter is Wizenmann’s example of the lover who infers the existence of their beloved’s reciprocal love, simply because the lover needs this to be the case. Kant responds to Wizenmann, and this example, primarily in the second Critique’s chapter ‘On Assent from A Need of Pure Reason’ (5:142–6)

I come to the final and, indeed, most important aid [Hülfsmittel] of patience, which is related to the preceding one—conviction of its accord with duty—in the most precise way. This aid is religious virtue, resignation to the divine will, which emerges from belief [Glauben] in God and from the hope of a better future.

Hermann Andreas Pistorius (1730–1798) was a pastor and frequent contributor to the Allgemeine deutsche Bibliothek, an important journal of the German Enlightenment. Pistorius reviewed nearly every one of Kant’s major works for the journal as well as many texts by both Kant’s defenders and critics. This chapter contains Pistorius’ review of Johann Schultz’s Elucidations of Herr Professor Kant’s Critique of Pure Reason, the first book-length commentary on the first Critique. In the review, Pistorius uses Schultz’s Elucidations as the occasion for examining some of Kant’s own doctrines directly, such as his theory of space and time and the distinction between appearances and things in themselves. Particularly relevant to the second Critique are Pistorius’ criticism of Kant’s solution to the third antinomy, his claim that the first Critique is inconsistent with the Groundwork, and the claim that Kant is illegitimately biased towards moral ideas.

The third and final review authored by Pistorius in this volume is his review of the second Critique. The review completes a fascinating exchange between Pistorius and Kant that begins with the former’s early review of Schultz’s Elucidations and the Groundwork, among others, continues with Kant’s responses to these reviews in the second Critique, and ends here with Pistorius’ review of the second Critique. In the review, Pistorius returns to some of the same points made in his previous reviews, such as the ‘priority of the good’ objection, the charge of empty formalism, and Kant’s conception of freedom. A major theme of the review is Pistorius’ inability to accept Kant’s distinction between the empirical and intelligible character of human beings, and other topics include a discussion of the highest good and Kant’s relationship to Stoic moral philosophy.

I consign myself to a new investigation of some of my statements, not to even further disturb the spirit of the philosophical Israelite, nor to reignite a conflict that burned so brightly once already, but solely and entirely with the intention of discharging a duty of deference that I owe. I had resolved to keep myself out of this affair from that time onwards, and to question in silence what I had justly or unjustly been accused of. For, I too am convinced that every truth must and will support itself, and even I could [117] not expect to be understood as I wanted, given so many different interests of so many different parties, even after many explanations. Unfortunately, my weak health supported this decision strongly enough and I would have stuck to it had you, venerable Kant!, not spoken out against me.

Kant did not initially intend to write the Critique of Practical Reason, let alone three Critiques. It was primarily the reactions to the Critique of Pure Reason and the Groundwork of the Metaphysics of Morals that encouraged Kant to develop his moral philosophy in the second Critique. In this brief introduction I outline some of the major events that took place in Kant’s development between the first and second Critiques. I illustrate that the story of the Critique of Practical Reason’s origin reveals that it is especially suited to being accompanied by certain background source materials that help illuminate its aims and contents.

On what kind of human action and omission is treated here. We find it grounded in experience that both some thoughts of the soul and some movements of the body stem from the will of the soul. Others, on the other hand, are not subject to the will (§325 Met.). For example: it is based on my [2] will that I now direct my thoughts to considering the good deeds of God, which he has shown me on previous occasions, but not that I see the person who encounters me or hear the shrieks of someone making noise (§219, 786 Met.), nor that I think of those things that occur to me in such circumstances (§238 Met.). No less does it stand under my will whether I now want to stand or sit, but not whether I digest the meal I have eaten or not (§519 Met.). What ranks among the actions of human beings. Since what stems from our will has its ground in the will (§29 Met.) and thus in us (§197 Met.), and similarly the movements of the body that are subject to the will have their ground in the state [Zustand]1 of the body (§878, 882 Met.), both the thoughts of the soul as well as the movements of the body that stem from the will rank among our actions (§104 Met.). Which are free. And since the will has a freedom to choose among possible things that which pleases us the most (§510 Met.), so are such human actions free, and therefore receive the name of free actions. To be precise, the movements of the body, by means of which the desires of the soul are fulfilled, are free with respect to the soul (§884, 885 Met.). On the other hand, since we encounter no freedom independently of the will (§492, 519 Met.), so is there also [3] no freedom in human action, whether it consists in thoughts of the soul or movements of the body, if it is not subjected to the will. Which are necessary. The action in such cases is necessary and therefore receives the name of a necessary action. Here we are only concerned with the free actions of human beings and in no way with those that are necessary.

August Wilhelm Rehberg (1757–1836) was a civil servant in Hanover, but he also made several important contributions to the philosophical debates of his time. This chapter contains the first English translation of Rehberg’s review of the second Critique, which was highly influential and read by figures such as Reinhold and possibly Fichte as well. In the review, Rehberg doubts that pure reason can be practical. One of the most important statements of the review is Rehberg’s claim that the feeling of respect must be something sensible and, as such, must contain an element of pleasure, despite what Kant says. Kant was aware of the review and is thought to have responded to it in later works such as the third Critique.

That it is neither unnecessary nor superfluous to elucidate Herr Prof. Kant’s Critique of Pure Reason, by means of which the content of this important but difficult to comprehend work is disclosed to those readers who lack the leisure time and patience, even if they are not entirely lacking in ability, to delve into the system of the deep-thinking philosopher, and disclose it in such a way that such readers are now able to understand its content with little effort and are able to busy their philosophical reflection with it, this, it seems to me, has been admitted by all experts and half-experts who have to some degree expressed themselves about it by complaining about the obscurity of the work. Herr second court chaplain Schulze has therefore done an agreeable and important service to philosophy and her devotees with these Elucidations, in that he has provided us with this clear commentary, approved by Herr Prof.