Kant's correspondence includes a short letter from a well-wisher named Bertram. The content of the letter is as harmless as it is uninteresting: Bertram invites Kant to visit his brother's estate. ‘Do come,’ he says, ‘because the weather is so beautiful and such travel so beneficial’ (10: 182). The interest of the letter is entirely exhausted by the date: 20 May 1775. For Kant used the letter to scribble down ideas, some suggestive of themes later to emerge in the first Critique. Similarity of handwriting and train of thought suggests that these scribbles are part of a whole bundle of papers collectively known as the Duisburg Nachlaβ (R4674-4684 in volume 17 of the Academy Edition). It was supposedly Kant's practice to use letters as scrap paper shortly after receiving them. If this is true, we can date the Bertram scribbles - and, in all likelihood, the bundle as a whole - to some time in 1775. That would make the Duisburg Nachlaβ one of the few pieces of philosophical writing in Kant's own hand to come down to us from the 1770s, and the only extended piece in his hand from the middle of the decade. It offers a rare glimpse of Kant at work on immediate ancestors of central ideas in the first Critique and might therefore be expected to shed light on an important chapter in Kant's philosophical development.

In recent times, a number of authors have systematically criticized Kant's 1768 ‘proof’ of the reality of absolute space. Peter Remnant may have been the first do to so, but many others have since joined him, either challenging the argument itself or showing how relationist conceptions of space can account for incongruent counterparts just as well as absolutist conceptions. In fact, Kant himself abandoned his main conclusion soon after publication, favouring instead the doctrine of transcendental idealism. I do not see how the 1768 proof can be saved, nor will I defend it here. However, in dismissing it some critics seem to have gone too far, and either failed to fully acknowledge Kant's contribution, or attributed to him thoughts he is unlikely to have had. Kant's treatment of incongruent counterparts in his Dissertation of 1770 has also met strong opposition. In particular, his claim that the difference between a pair of incongruent counterparts cannot be apprehended by means of concepts alone has been taken to be a mathematical falsehood. Indeed, incongruent counterparts have been shown to be mathematically distinguishable, with no intuitions needed for that purpose.

All duties are either duties of right (officia iuris), that is, duties for which external lawgiving is possible, or duties of virtue (officia virtutis s. ethica), for which external lawgiving is not possible. - Duties of virtue cannot be subject to external lawgiving simply because they have to do with an end which (or the having of which) is also a duty. No external lawgiving can bring about someone's setting an end for himself (because this is an internal act of the mind), although it may prescribe external actions that lead to an end without the subject making it his end. (Immanuel Kant, The Metaphysics of Morals)

Kant's description of an enlightened society as involving the free use of reason in public debate has received due attention in recent work on Kant. When thinking of Kant's view of Enlightenment, one now conjures up the image of free persons speaking their mind in what is now often called the ‘public sphere’. Jürgen Habermas is well known for taking Kant to be committed to wide participation of individuals in public debate. Kant's own suggestion for a motto for the Enlightenment, ‘Sapere aude’, seems to speak to all citizens when urging them to ‘Have courage to make use of your own understanding’ (8: 35).

In his Groundwork of the Metaphysics of Morals (1784), Kant explains that ethics, like physics, ‘will have its empirical part, but it will also have a rational part, … though here [in ethics] the empirical part might be given the special name practical anthropology’ (4: 388). In the Groundwork, Kant suggests that anthropology, or the ‘power of judgment sharpened by experience’, has two roles, ‘to distinguish in what cases [moral laws] are applicable’ and ‘to gain for [moral laws] access to the human will’ (4: 389). Twelve years later, the first function, of applying the categorical imperative to specifically human situations, is incorporated into Kant's Metaphysics of Morals (1797).

Kant rejected ‘theological morality’, insisting that no one, including God, can be the ‘author’ of the moral law because the moral law is a categorically necessary, non-positive law. Kant was also no religious enthusiast and clearly intended to rule out certain kinds of dependence of ethics on theology. Such considerations make it tempting to suggest that Kant was fully committed to what has been called the ‘autonomy of ethics’ from theology. Yet an observant reader of Kant's corpus is constantly confronted with passages in which Kant discusses philosophical theology, connections between moral philosophy and theology, and even argues that we should ‘recognize all our duties as divine commands’ (KpV, 5: 129).