A painting of Immanuel Kant in his middle age
Immanuel Kant (April 22, 1724 – February 12, 1804) was a German philosopher from Prussia, generally regarded as one of Europe's most influential thinkers and the last major philosopher of the Enlightenment. He had a major impact on the Romantic and Idealist philosophies of the 19th century, and his work was the starting point for Hegel.
Kant is best known for his view — called transcendental idealism — that we bring innate forms and concepts to the raw experience of the world, which would otherwise be unknowable. We perceive the world by means of our senses and innate intuitions, he argued, and therefore the thing-in-itself cannot be known. Our objects of knowledge, filtered by our senses, are simply appearances.
His epistemology, or theory of knowledge, was an attempt to solve the conflict between the rationalists, who said that knowledge without experience is possible, and the empiricists, who argued that experience is all there is. Kant bridged the gap between these two positions with the opening statement of his Critique of Pure Reason: "But though all our knowledge begins with experience, it does not follow that it all arises out of experience." 
Kant was born, lived and died in Königsberg, the capital of East Prussia, a city which today is Kaliningrad in the Russian exclave of that name. His parents baptized him as Emanuel Kant, which he later, after learning Hebrew, changed to Immanuel. He spent much of his youth as a solid, albeit unspectacular, student. Contrary to the dour image of him promoted by early biographers, Kant as a young man was quite gregarious and enjoyed attending social events about town. He also regularly invited guests over for dinner, insisting that company and laughter were good for his constitution. It was only after befriending the English merchant Joseph Green, who instilled in Kant a respect for living according to strictly observed maxims of behavior, that Kant began living a very regulated life: according to some stories neighbors would set their clocks according to the time Green and Kant finished their daily get-togethers. A biography of Kant by Manfred Kuehn even suggests that Kant was philosophically inspired by Green, who not only recommended him to the philosophy of David Hume, but whose personal habits may have influenced Kant in formulating his idea of the categorical imperative.  Another influential view about the introduction of the works of Hume to Kant and other German philosophers, which finds its clearest expression in the works of Frederick C. Beiser, is that it was Johann Georg Hamann (1730-1788) who brought Hume's views to Germany. For the remainder of his life Kant remained unmarried and owned only one piece of art in his household, advocating the absence of passion in favor of logic. He never left Prussia and rarely stepped outside his own home town. He was a respected and competent university professor for most of his life, although he was in his late fifties before he did anything that would bring him historical repute.
He entered the local university in 1740, and studied the philosophy of Leibniz and Christian Wolff under Martin Knutsen, a follower of Wolff. He also studied the new mathematics of Sir Isaac Newton and, in 1746, wrote a paper on measurement, reflecting Leibniz's influence. In 1755, he became a private lecturer at the University, and while there published "Inquiry into the Distinctness of the Principles of Natural Theology and Morals", where he examined the problem of having a logical system of philosophy that connected with the world of natural philosophy, a concern typical of the period. In this paper, he proposed what later become known as the Kant-Laplace theory of planetary formation, wherein the planets formed from rotating protoplanetary disks of gas. Kant was also the first recorded scholar to postulate (as is true) that some of the faint nebulae one can see with a small telescope (or in one case, with the naked eye) were external galaxies or, as he called them, island universes. Kant's prescient remarks on island universes.
In 1763, he wrote The Only Possible Ground of Proof for a Demonstration of God's Existence, which questioned the ontological argument for God put forward by Saint Anselm of Canterbury in the 11th century, namely that the greatest of all possible ideas must include the attribute of existence, because if it does not, it is not the greatest of all possible ideas. Therefore, God, who by definition is the greatest of all possible ideas, must exist. Rene Descartes put forward a similar argument in the Fifth Meditation. Despite questioning this argument however, Kant in this piece defends a modified form of rational theology, which he subsequently rejected in his Critical work.
In 1766, he was appointed Second Librarian of the Royal Library, a prestigious government position. In 1770, he became a full professor at Königsberg. It was after this time that Hume's works began to have serious impact on his understanding of metaphysics though there is considerable evidence he had read Hume earlier and that it was only the breakdown of an early attempt at constructing a rationalist metaphysics that led him to see Hume's contribution to philosophy as decisive. Hume was fiercely empirical, scorned all metaphysics, and systematically debunked great quantities of it. His most famous thesis is that nothing in our experience can justify the assumption that there are "causal powers" inherent in things — that, for example, when one billiard ball strikes another, the second must move. Kant found Hume's conclusions unacceptable. "I wilfully admit that it was David Hume that woke me from my dogmatic slumber", he would later write.
For the next 10 years, he worked on the architecture of his own philosophy. In 1781, he released the Critique of Pure Reason, one of the most influential, widely cited, and widely disputed works in Western philosophy. He followed this with Groundwork of the Metaphysics of Morals, then in 1788, the Critique of Practical Reason and in 1790, the Critique of Judgement. The effect was immediate in the German-speaking world, with readership including Ludwig van Beethoven and Johann Wolfgang von Goethe. But the attention was far from universally approving: on the contrary, almost every aspect of his writing was attacked and criticized fiercely, particularly his ideas on categories, the place of free will and determinism, and whether we can have knowledge of external reality. His early critics included Johann Schaumann , Friedrich Heinrich Jacobi and Hermann Pistorius . Pistorius' criticisms were particularly influential and are still cited today.
The Critique of Practical Reason dealt with morality, or action, in the same way that the first Critique dealt with knowledge, and the Critique of Judgement dealt with the various uses of our mental powers that neither confer factual knowledge nor determine us to action, such as aesthetic judgement, for example of the beautiful and sublime, and teleological judgment, that is, construing things as having "purposes". As Kant understood them, aesthetic and teleological judgment connected our moral and empirical judgments to one another, unifying his system. Two shorter works, the Prolegomena to any Future Metaphysics and the Groundwork to the Metaphysics of Morals treated the same matter as the first and second critiques respectively, in a more cursory form — assuming the answer and working backward, so to speak. They serve as his introductions to the critical system.
The epistemological material of the first Critique was put into application in the Metaphysical Foundations of Natural Science; the ethical dictums of the second were put into practice in Metaphysics of Morals. His work on moral philosophy is best known for its formulation of a basic tenet of ethics, sometimes falsely assumed to be an extension of the Golden Rule, which Kant called the categorical imperative: "Act only on that maxim whereby thou canst at the same time will that it should become a universal law."
Kant also wrote a number of semi-popular essays on history, politics, and the application of philosophy to life. When he died in 1804, he was working on an incomplete manuscript that has been published as Opus Postumum .
His tomb and its pillared enclosure outside the cathedral in Königsberg is one of the few artifacts of German times preserved by the Soviets after they conquered East Prussia in 1945. A replica of a statue of Kant that stood in front of the university was donated by a German entity in 1991 and placed on the original pediment. The inscription near his tomb, in German and Russian, reads:
- Two things fill the mind with ever new and increasing admiration and awe, the more often and perseveringly my thinking engages itself with them: the starry heavens above me and the moral law within me.
The Critique of Pure Reason
Kant's most widely read and most influential book is Critique of Pure Reason  (1781) - his attempt to work past what he saw as the unacceptable conclusions of David Hume. Kant wanted to find the limitations of Reason, and its application to such important philosophical questions as whether there is a God, the immortality of the soul, and freedom. A person who studies Kant's Critique of Pure Reason, should also study Hume's Enquiry Concerning Human Understanding in order to understand what caused Kant to become so interested in writing his three Critiques.
Hume's conclusions, Kant realized, rested on the premise that knowledge is empirical at its root. The problem that Hume identified was that basic principles like cause and effect cannot be empirically derived. Kant's goal, then, was to find some way to derive cause and effect without relying on empirical knowledge. Kant rejects analytical methods for this, arguing that analytic reasoning can't tell you anything that isn't already self-evident. Instead, Kant argued that we would need to use synthetic reasoning. But this posed a new problem - how can one have synthetic knowledge that is not based on empirical observation - that is, how can we have synthetic a priori truths. Kant's famous quote from the first third of the book is, “thoughts without content [are] empty, and intuitions without concepts [are] blind.”
Kant did not have any trouble showing that we do have synthetic a priori truths. After all, he reasoned, geometry and Newtonian physics are synthetic a priori knowledges and are fundamentally true. The issue was showing how one could ground synthetic a priori knowledge for a study of metaphysics. This led to his most influential contribution to metaphysics - the abandonment of the quest to try to know the world in itself, instead acknowledging that there is no way to determine whether something is experienced the way it is because that's the way it is, or because the faculties we have with which to perceive and experience are constructed such that we experience it in a given way. He demonstrated this with a thought experiment, showing that we cannot meaningfully conceive of an object that exists outside of time and has no spatial components. Although we cannot conceive of such an object, Kant argues, there is no way of showing that such an object does not exist. Therefore, Kant says, metaphysics must not try to talk about what exists, but instead about what is perceived, and how it is perceived.
This insight allows Kant to set up a distinction between phenomena and noumena - phenomena being that which can be experienced, and noumena being things that are beyond the possibility of experience - things in themselves. Nothing can be truly experienced or else you would experience the noumenon itself. The phenomenon is only the representation of the object/noumenon that a person receives through their sensibilities. The phenomenon is a representation of an object not the object itself, nothing more. Kant then discussed and expanded on the faculties of experience we have, and thus was able to come up with a system of metaphysics that applied to the world as we perceive it.
Kant termed his critical philosophy "transcendental idealism." While the exact interpretation of this phrase is contentious, one way to start to understand it is through Kant's comparison in the second preface to the "Critique of Pure Reason" of his critical philosophy to Copernicus' revolution in astronomy. Kant writes: "Hitherto it has been assumed that all our knowledge must conform to objects. But all attempts to extend our knowledge of objects by establishing something in regard to them a priori, by means of concepts, have, on this assumption, ended in failure. 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" [Bxvi]. Just as Copernicus revolutionized astronomy by changing the point of view, Kant's critical philosophy asks what the a priori conditions for our knowledge of objects in the world might be. Transcendental idealism describes this method of seeking the conditions of the possibility of our knowledge of the world.
Kant's "transcendental idealism" should be distinguished from idealistic systems such as Berkeley's. While Kant claimed that phenomena depend upon the conditions of sensibility, space and time, this thesis is not equivalent to mind-dependence in the sense of Berkeley's idealism. For Berkeley, something is an object only if it can be perceived. For Kant, on the other hand, perception does not provide the criterion for the existence of objects. Rather, the conditions of sensibility - space and time - provide the "epistemic conditions", to borrow a phrase from Henry Allison, required for us to know objects in the phenomenal world.
Kant had wanted to discuss metaphysical systems but discovered "the scandal of philosophy" — you cannot decide what the proper terms for a metaphysical system are until you have defined the field, and you cannot define the field until you have defined the limit of the field of physics first.
'Physics' in this sense means, roughly, the discussion of the perceptible world.
Kant's idea that Judgment cannot be taught
As stated in Immanuel Kant’s, “Critique of Pure Reason,” “A person can have tremendous understanding of the sciences, but that does not mean they will have the correct judgment to rightfully apply the understanding.” The judgment cannot be taught, it can only be sharpened through experience. According to Kant, “Thus, it is evident that the understanding is capable of being instructed by rules, but that the judgment is a peculiar talent, which does not, and cannot require tuition, but only exercise. This faculty is therefore the specific quality of the so-called mother wit, the want of which no scholastic discipline can compensate. For although education may furnish, and, as it were engraft upon a limited understanding of rules borrowed from other minds, yet the power of employing these rules correctly must belong to the pupil himself; and no rule which we can prescribe to him with this purpose is , in the absence or deficiency of this gift of nature, secure from misuse. A physician therefore, a judge or a statesman, may have in his head many admirable pathological, juridical, or political rules, in a degree that may enable him to be a profound teacher in his particular science, and yet in the application of these rules he may very possibly blunder-either because he is wanting in natural judgment (though not in understanding) and, whilst he can comprehend the general in abstracto, cannot distinguish whether a particular case in concreto ought to rank under the former; or because his faculty of judgment has not been sufficiently exercised by example and real practice. Indeed, the grand and only use of examples is to sharpen the judgment. (Kant, Critique of Pure Reason, Of the Transcendental Faculty of Judgment in General).”
Kant's Postulates in the Transcendental Analytic
In the Transcendental Analytic Kant presents the three postulates: the possible, actual, and necessity. Kant states that the postulate of the possibility of things requires that the concept of the things should agree with the formal conditions of an experience, with the conditions of intuition and concepts, in general (Kant, A220). What agrees with the formal conditions of experience is possible, and everything that does not agree with it is not possible; experience validates concepts. Kant states that an empty concept is that which contains a synthesis and is not related to any object, if this synthesis does not belong to experience either as derived from it, in which case it is an empirical concept, or as being on a prior condition upon which experience in general in its formal aspects rest, in which case it is a pure concept.
In order to be valid a concept, it is indeed a necessary logical condition that a concept of the possible must not contain any contradiction. This idea of a concept not having a contradiction is very important due to Kant's use of it in developing a morality and ethics; an example will be given later in this essay as a demonstration. Even if a concept does not have a contradiction this by itself is not sufficient to make the concept valid nor by any means sufficient to determine objective reality of a concept. An example of a concept that contains no contradiction but is not valid is the concept of a figure enclosed within two straight lines, although it contains no contradiction it is not valid (Kant, A221). As Kant states the impossibility arises in the connection with its construction in space.
Having stated postulate #1, Kant then explains what happens if we do not stick to his definition of it. Kant explains that if we should seek to frame quite new concepts of substances, forces, reciprocal actions, from the material which perception presents to us, without experience itself yielding the example of their connection, we should be occupying ourselves with mere fancies, of whose possibility there is no criterion since we have neither borrowed these concepts directly from experience, nor have taken experience as our instructress in their formation (Kant, A222). An example of a concept commonly held by intellectuals during his time, and still held by contemporaries, would be those of psychic and remote viewing. Kant defines these two concepts as a substance which would be permanently present in space, but without filling it (like that mode of existence intermediate between matter and thinking being which some would seek to introduce), or a special ultimate mental power of intuitively anticipating the future (and not merely inferring it), or lastly a power of standing in community of thought with other men, however distant they may be-are concepts the possibility of which is altogether groundless, as they cannot be based on experience and its known laws as the example of Immanuel Sweden Borg (Kant, B270). Kant ends his discussion of the possibility postulate by stating that in order to think inconcreto, you must call experience to you aid.
After defining the postulate of the possible Kant then explains the postulate of actuality. Kant states that in order for a concept to be actual it does not demand immediate perception (and therefore, sensation of which we are conscious) of the object whose existence is to be known. Kant states that if a concept precedes perception this signifies the concept mere possibility, in order to be actual perception must supply the content to the concept for its sole mark of actuality. An example of a concept that has fulfilled the actuality postulate would be magnetism. Kant states that thus from the perception of the attracted iron filings we know of the existence of a magnetic matter pervading all bodies, although the constitution of our organs cuts us off from all immediate perception of this medium (Kant, A226). Another example of a concept that fulfills the actuality postulate would be gravity.
Kant rejects material idealism which states that the existence of objects in space outside of us either to be merely doubtful and indemonstrable (Descartes) or to be false and impossible (Berkley). Problematic Idealism, lead by Descartes, states that the only empirical assertion that is certain is “I am.” Kant states that in order to overcome problematic idealism a proof must show that we have experience, not merely an imagination of things. Dogmatic Idealism, lead by Bishop Berkley, states that things in space are imaginary entities, and Kant claims that he already refuted this claim in the Transcendental Aesthetic.
The thesis Kant uses to refute idealism states that the mere, but empirically determined, consciousness of my own existence proves the existence of objects in space outside me. (1.) In order to prove the existence of objects outside of him he states that he is conscious of his own existence a determined in time. (2.) All determinations of time presuppose something permanent in perception. (3) The permanent cannot be in me, since it is only through the permanent that my existence in time can itself be determined. Kant concludes by stating that, “Thus perception of this permanent is possible only through a thing outside me and not through the mere representation of a thing outside me; and consequently the determination of my existence in time is possible only through the existence of an actual thing which I perceive outside me.”
Kant states that the “game of idealism” has been turned against itself. Idealism, he states, assumes that only immediate experience is inner experience, and from it we can only infer outer thing only in an untrustworthy manner, so the cause of the representation, which we ascribe, perhaps falsely to outer things may be in ourselves. For Kant outer experience is immediate through time determination. Although it is immediate experience it does not immediately include any knowledge of subject no empirical knowledge. For Kant inner experience is itself possible only relating through out experience.
Kant's third postulate is the material necessity in existence. He states that objects of the senses cannot be known completely a priori, but only comparatively a priori. He states that concepts which in its connection with the actual is determined in accordance with the universal conditions of experience, is (that is, exist as) necessary. Kant argues that nothing happens through blind chance. He claims that no necessity in nature is blind, but always conditional and intelligibly necessary. Nature also forbids any leap on the senses of appearance, and forbids any gap of cleft between appearances.
Kant's moral philosophy
Kant developed his moral philosophy in three works: Groundwork of the Metaphysic of Morals  (1785), Critique of Practical Reason  (1788), and Metaphysics of Morals  (1798).
Kant is known for his theory that there is a single moral obligation, which he called the Categorical Imperative, from which all other moral obligations are generated. He believed that the moral law must be a principle of reason itself, and could not be based on contingent facts about the world (e.g., what would make us happy). Accordingly, he believed that moral obligation applies to all and only rational agents.
A categorical imperative is an unconditional obligation; that is, it has the force of an obligation regardless of our will or desires. (Contrast this with hypothetical imperative.) Kant's categorical imperative was formulated in three ways, which he believed to be roughly equivalent (although many commentators do not):
- The first formulation (Formula of Universal Law) says: "Act only in accordance with that maxim through which you can at the same time will that it become a universal law."
- The second formulation (Formula of Humanity) says: "Act that you use humanity, whether in your own person or in the person of any other, always at the same time as an end, never merely as a means."
- The third formulation (Formula of Autonomy) is a synthesis of the first two. It says that we should so act that we may think of ourselves as legislating universal laws through our maxims. We may think of ourselves as such autonomous legislators only insofar as we follow our own laws.
Example of the first formulation: The most popular interpretation of the first formulation is called the "universalizability test." An agent's maxim, according to Kant, is his "subjective principle of volition" — that is, what the agent believes is his reason to act. The universalizability test has five steps:
1. Find the agent's maxim.
2. Imagine a possible world in which everyone in a similar position to the real-world agent followed that maxim.
3. Decide whether any contradictions, or irrationalities, arise in the possible world as a result of following the maxim.
4. If a contradiction or irrationality arises, acting on that maxim is not allowed in the real world.
5. If there is no contradiction, then acting on that maxim is permissible, and in some instances required.
There are two types of contradiction that Kant thinks may arise with impermissible maxims. The first type he calls "contradictions in conception." Kant uses the example of a false promise to illustrate this. His imagined agent has the maxim: "I am going to lie so that someone will lend me money, because I am in need." Kant argues that universalizing this maxim would lead to a contradiction — that is, if everyone were to follow this maxim, and were to lie whenever in need, promises would mean nothing. So it would be contradictory or irrational to make a false promise to secure money, since your promise would simply be laughed at. Thus, acting on such a maxim is impermissible, which means we have a duty not to make false promises just to satisfy our needs. Incidentally, Kant believed that any maxim involving lying would lead to a contradiction, leading to his commitment to the view that we have a perfect (i.e. inviolable) duty not to lie.
The second type of contradiction Kant calls "contradictions in will," which arise when a universalized maxim would contradict something the agent would have to will as a rational being. Kant's example involves a self-reliant person who thinks everybody should mind their own business, and thus acts on the maxim: "Don't help others." In the imagined world where this is universalized, Kant thinks that this would necessarily contradict something any rational agent must will, namely that if one is in great need and could easily be helped by another, as a rational being he would have to will that the other person help him — but this universalized maxim contradicts that, thus leading to a contradiction in will, and showing that the policy, "Don't help others" is impermissible.
Example of the second formulation: If I steal a book from you, I am treating you as a means only (to obtain a book). If I ask to have your book, I am respecting your right to say no, and am thereby treating you as an end-in-yourself, not as a means to an end.
Kant's applied his categorical imperative to the issue of suicide in Groundwork of the Metaphysic of Morals, writing that:
[I]f a man is reduced to despair by a series of misfortunes and feels wearied of life, but is still so far in possession of his reason that he can ask himself whether it would not be contrary to his duty to himself to take his own life, he should ask himself a question. He should inquire whether the maxim of his action could become a universal law of nature. His maxim is: From self-love I adopt it as a principle to shorten my life when its longer duration is likely to bring more evil than satisfaction. It is asked then simply whether this principle founded on self-love can become a universal law of nature. Now we see at once that a system of nature of which it should be a law to destroy life by means of the very feeling whose special nature it is to impel to the improvement of life would contradict itself, and therefore could not exist as a system of nature; hence the maxim cannot possibly exist as a universal law of nature, and consequently would be wholly inconsistent with the supreme principle of all duty.
The theory that we have universal duties, which hold despite one's own inclinations or the desire to pursue one's own happiness instead, is known as deontological ethics.
Kant is often cited as the most important source of this strand of ethical theory; in particular, of the theory of conduct, also known as the theory of obligation.
Kant's moral philosophy has come under criticism as his lectures on anthropology have been further examined. Critics have argued that statements such as "All races will die out except for that of the whites," and that Africans are born for slavery, indicate that he does not consider non-whites to be persons in any meaningful ethical sense. This interpretation is by no means dominant. The standard account is that Kant's universalism is at times marred by incorrect empirical views of non-whites, rather than by a developed philosophical doctrine of white supremacy.
Kant's most famous works are his critiques, particularly his Critique of Pure Reason, which respond to the problem of the scandal of reality, and are rooted in his reactions to David Hume and Rene Descartes, as well as Leibniz and Christian Wolff. The works of these writers forms a useful background to Kant's world and work. The work of Kant's student Fichte is also useful in understanding the process by which Kant's work was made accessible to others at that time, and for a basis for the schools of interpretation of Kant's work.
The body of literature on Kant continues to grow.
Often, the best places to start are the introductions of his translated works. Modern translations usually suggest a variety of secondary literature, the purpose of which is both to explain and to interpret Kant's philosophy.
For an example, see Christine Korsgaard's introduction to Mary Gregor 's translation of the Groundwork, which not only provides a concise overview of Kant's moral philosophy, but also places his ethics within the framework of the larger critical system. Kant wrote for an audience that was familiar with medieval philosophy and the philosophy of Leibniz. The reader of today who happens not to be familiar with these parts of the philosophical tradition can be greatly hampered by lacking an adequate knowledge of technical vocabulary and historical context. Another well regarded work is Kant's Metaphysics and Theory of Science by Gottfried Martin. The English translation was published by the University of Manchester, University Press, 1955.
Contemporary historian Christine Korsgaard has published Creating the Kingdom of Ends, which provides an exigesis of Kant's view with respect to such moral systems as presented by Aristotle, Hume, and Hegel. A shorter defense and interpretation of Kant's theories is can be seen in Barbara Herman 's collection of essays, The Practice of Moral Judgement. Both Korsgaard and Herman were students of John Rawls, who helped to re-invigorate Kantian ethics in the 20th century.
John Rawls' own book of published lecture notes, titled Lectures on the History of Moral Philosophy, is an excellent starting point for someone who is reading Kant for the first time. The work is particularly useful in its investigation of Kant's moral philosophy within the vicissitudes of ethical systems from Hume to Leibniz to Hegel.
Two other important scholars of Kant are Henry Allison and Onora O'Neill. Both authors have written books about Kant's moral philosophy.
For an introductory account to many aspects of Kant's theoretical and practical philosophy, see The Cambridge Companion to Kant, ed. Paul Guyer . Henry Allison 's book, Kant's Transcendental Idealism, provides a thorough and sympathetic account of Kant's theoretical philosophy, arguing for the centrality of "transcendental idealism" for understanding Kant. Beatrice Longuenesse 's Kant and the Capacity to Judge, provides a careful, well-argued, though difficult, argument for the importance of the metaphysical deduction of the categories as well as reinterpretations of many of the central doctrines of the first Critique.
Kant's ideas have achieved some prominence in applied ethics. For example, Norman Bowie 's book, Business Ethics: A Kantian Perspective, focuses on the requirement for social cooperation in a business, in which people, conceived collectively, are to be treated as a "kingdom of ends." Another example is to be found in Michael E. Berumen's book, Do No Evil: Ethics with Applications to Economic Theory and Business, which adopts a Kantian approach to making exceptions to basic moral rules, and also offers several practical examples of how ethical problems in business might be solved using Kantian analysis.
Works and links to texts, in English and German
- Immanuel Kant (1902) Reflexionen zur anthropologie. In Gesammelte Schriften., volume XV, pages 55-899. Hrsg. von der Königlich-Preussischen Akademie der Wissenschaften zu Berlin, Berlin, 1902-
- Brigitte Sassen (2000), ed., Kant's Early Critics: The Empiricist Critique of the Theoretical Philosophy
- Kuehn, Manfred. Kant: A Biography. Cambridge University Press, 2002 ISBN 0521524067
- "Meet Mr Green", The Economist, May 3, 2001, retrieved March 19, 2005