Immanuel Kant

Section 26: About Immanuel Kant

Immanuel Kant (22 April 1724 – 12 February 1804) was a German philosopher (a native of the Kingdom of Prussia) and one of the central Enlightenment thinkers. Born in Königsberg, Kant’s comprehensive and systematic works in epistemology, metaphysics, ethics, and aesthetics have made him one of the most influential figures in modern Western philosophy. In his doctrine of transcendental idealism, Kant argued space and time are mere “forms of intuition” that structure all experience and that the objects of experience are mere “appearances”. The nature of things as they are in themselves is unknowable to us. In an attempt to counter the philosophical doctrine of skepticism, he wrote the Critique of Pure Reason (1781/1787), his most well-known work. Kant drew a parallel to the Copernican revolution in his proposal to think of the objects of experience as conforming to our spatial and temporal forms of intuition and the categories of our understanding, so that we have a priori cognition of those objects. Kant believed that reason is the source of morality, and that aesthetics arises from a faculty of disinterested judgment. Kant’s religious views were deeply connected to his moral theory. Their exact nature, however, remains in dispute. He hoped that perpetual peace could be secured through universal democracy and international cooperation. His cosmopolitan reputation, however, is called into question by his promulgation of scientific racism for much of his career, even though he changed those views in the last decade of his life.


Immanuel Kant was born on 22 April 1724 into a Prussian German family of Lutheran Protestant faith in Königsberg, East Prussia (since 1946 the Russian city of Kaliningrad). His mother, Anna Regina Reuter (1697–1737), was born in Königsberg to a father from Nuremberg. Her surname is sometimes erroneously given as Porter. Kant’s father, Johann Georg Kant (1682–1746), was a German harness-maker from Memel, at the time Prussia’s most northeastern city (now Klaipėda, Lithuania). It is possible that Kants got their name from the village of Kantvainiai (German: Kantwaggen – today part of Priekulė) and were of Kursenieki origin. Baptized Emanuel, Kant later changed the spelling of his name to Immanuel after learning Hebrew. He was the fourth of nine children (six of whom reached adulthood). The Kant household stressed the pietist values of religious devotion, humility, and a literal interpretation of the Bible. The young Immanuel’s education was strict, punitive and disciplinary, and focused on Latin and religious instruction over mathematics and science. In his later years, Kant lived a strictly ordered life. It was said that neighbors would set their clocks by his daily walks. He never married but seems to have had a rewarding social life; he was a popular teacher as well as a modestly successful author, even before starting on his major philosophical works.

Young scholar

Kant showed a great aptitude for study at an early age. He first attended the Collegium Fridericianum from which he graduated at the end of the summer of 1740. In 1740, aged 16, he enrolled at the University of Königsberg, where he spent his whole career. He studied the philosophy of Gottfried Leibniz and Christian Wolff under Martin Knutzen (Associate Professor of Logic and Metaphysics from 1734 until his death in 1751), a rationalist who was also familiar with developments in British philosophy and science and introduced Kant to the new mathematical physics of Isaac Newton. Knutzen dissuaded Kant from the theory of pre-established harmony, which he regarded as “the pillow for the lazy mind”. He also dissuaded Kant from idealism, the idea that reality is purely mental, which most philosophers in the 18th century regarded in a negative light. The theory of transcendental idealism that Kant later included in the Critique of Pure Reason was developed partially in opposition to traditional idealism. Kant had contacts with students, colleagues, friends and diners who frequented the local Masonic lodge. His father’s stroke and subsequent death in 1746 interrupted his studies. Kant left Königsberg shortly after August 1748; he would return there in August 1754. He became a private tutor in the towns surrounding Königsberg, but continued his scholarly research. In 1749, he published his first philosophical work, Thoughts on the True Estimation of Living Forces (written in 1745–1747).

Early work

Kant is best known for his work in the philosophy of ethics and metaphysics, but he made significant contributions to other disciplines. In 1754, while contemplating on a prize question by the Berlin Academy about the problem of Earth’s rotation, he argued that the Moon’s gravity would slow down Earth’s spin and he also put forth the argument that gravity would eventually cause the Moon’s tidal locking to coincide with the Earth’s rotation. The next year, he expanded this reasoning to the formation and evolution of the Solar System in his Universal Natural History and Theory of the Heavens. In 1755, Kant received a license to lecture in the University of Königsberg and began lecturing on a variety of topics including mathematics, physics, logic, and metaphysics. In his 1756 essay on the theory of winds, Kant laid out an original insight into the Coriolis force. In 1756, Kant also published three papers on the 1755 Lisbon earthquake. Kant’s theory, which involved shifts in huge caverns filled with hot gases, though inaccurate, was one of the first systematic attempts to explain earthquakes in natural rather than supernatural terms. In 1757, Kant began lecturing on geography making him one of the first lecturers to explicitly teach geography as its own subject. Geography was one of Kant’s most popular lecturing topics and, in 1802, a compilation by Friedrich Theodor Rink of Kant’s lecturing notes, Physical Geography, was released. After Kant became a professor in 1770, he expanded the topics of his lectures to include lectures on natural law, ethics, and anthropology, along with other topics. In the Universal Natural History, Kant laid out the Nebular hypothesis, in which he deduced that the Solar System had formed from a large cloud of gas, a nebula. Kant also correctly deduced that the Milky Way was a large disk of stars, which he theorized formed from a much larger spinning gas cloud. He further suggested that other distant “nebulae” might be other galaxies. These postulations opened new horizons for astronomy, for the first time extending it beyond the solar system to galactic and intergalactic realms.

From then on, Kant turned increasingly to philosophical issues, although he continued to write on the sciences throughout his life. In the early 1760s, Kant produced a series of important works in philosophy. The False Subtlety of the Four Syllogistic Figures, a work in logic, was published in 1762. Two more works appeared the following year: Attempt to Introduce the Concept of Negative Magnitudes into Philosophy and The Only Possible Argument in Support of a Demonstration of the Existence of God. By 1764, Kant had become a notable popular author, and wrote Observations on the Feeling of the Beautiful and Sublime; he was second to Moses Mendelssohn in a Berlin Academy prize competition with his Inquiry Concerning the Distinctness of the Principles of Natural Theology and Morality (often referred to as “The Prize Essay”). In 1766 Kant wrote a critical piece on Emanuel Swedenborg’s Dreams of a Spirit-Seer.

On 31 March 1770, aged 45, Kant was finally appointed Full Professor of Logic and Metaphysics (Professor Ordinarius der Logic und Metaphysic) at the University of Königsberg. In defense of this appointment, Kant wrote his inaugural dissertation (Inaugural-Dissertation) De Mundi Sensibilis atque Intelligibilis Forma et Principiis (On the Form and Principles of the Sensible and the Intelligible World). This work saw the emergence of several central themes of his mature work, including the distinction between the faculties of intellectual thought and sensible receptivity. To miss this distinction would mean to commit the error of subreption, and, as he says in the last chapter of the dissertation, only in avoiding this error does metaphysics flourish. It is often claimed that Kant was a late developer, that he only became an important philosopher in his mid-50’s after rejecting his earlier views. While it is true that Kant wrote his greatest works relatively late in life, there is a tendency to underestimate the value of his earlier works. Recent Kant scholarship has devoted more attention to these “pre-critical” writings and has recognized a degree of continuity with his mature work.

Publication of The Critique of Pure Reason

At age 46, Kant was an established scholar and an increasingly influential philosopher, and much was expected of him. In correspondence with his ex-student and friend Markus Herz, Kant admitted that, in the inaugural dissertation, he had failed to account for the relation between our sensible and intellectual faculties. He needed to explain how we combine what is known as sensory knowledge with the other type of knowledge – that is, reasoned knowledge – these two being related, but having very different processes. Kant also credited David Hume with awakening him from a “dogmatic slumber” in which he had unquestioningly accepted the tenets of both religion and natural philosophy. Hume, in his 1739 Treatise on Human Nature, had argued that we only know the mind through a subjective, essentially illusory series of perceptions. Ideas such as causality, morality, and objects are not evident in experience, so their reality may be questioned. Kant felt that reason could remove this skepticism, and he set himself to solving these problems. Although fond of company and conversation with others, Kant isolated himself, and resisted friends’ attempts to bring him out of his isolation. When Kant emerged from his silence in 1781, the result was the Critique of Pure Reason. Kant countered Hume’s empiricism by claiming that some knowledge exists inherently in the mind, independent of experience. He drew a parallel to the Copernican revolution in his proposal that worldly objects can be intuited a priori, and that intuition is consequently distinct from objective reality. He acquiesced to Hume somewhat by defining causality as a “regular, constant sequence of events in time, and nothing more”.

Although now uniformly recognized as one of the greatest works in the history of philosophy, this Critique disappointed Kant’s readers upon its initial publication. The book was long, over 800 pages in the original German edition, and written in a convoluted style. Kant was quite upset with its reception. His former student, Johann Gottfried Herder criticized it for placing reason as an entity worthy of criticism instead of considering the process of reasoning within the context of language and one’s entire personality. Similar to Christian Garve and Johann Georg Heinrich Feder, he rejected Kant’s position that space and time possessed a form that could be analyzed. Additionally, Garve and Feder also faulted Kant’s Critique for not explaining differences in perception of sensations. Its density made it, as Herder said in a letter to Johann Georg Hamann, a “tough nut to crack”, obscured by “all this heavy gossamer”. Its reception stood in stark contrast to the praise Kant had received for earlier works, such as his Prize Essay and shorter works that preceded the first Critique. Recognizing the need to clarify the original treatise, Kant wrote the Prolegomena to any Future Metaphysics in 1783 as a summary of its main views. Shortly thereafter, Kant’s friend Johann Friedrich Schultz (1739–1805), a professor of mathematics, published Explanations of Professor Kant’s Critique of Pure Reason (Königsberg, 1784), which was a brief but very accurate commentary on Kant’s Critique of Pure Reason.

Kant’s reputation gradually rose through the latter portion of the 1780s, sparked by a series of important works: the 1784 essay, “Answer to the Question: What is Enlightenment?”; 1785’s Groundwork of the Metaphysics of Morals (his first work on moral philosophy); and, from 1786, Metaphysical Foundations of Natural Science. But Kant’s fame ultimately arrived from an unexpected source. In 1786, Karl Leonhard Reinhold published a series of public letters on Kantian philosophy. In these letters, Reinhold framed Kant’s philosophy as a response to the central intellectual controversy of the era: the pantheism controversy. Friedrich Jacobi had accused the recently deceased Gotthold Ephraim Lessing (a distinguished dramatist and philosophical essayist) of Spinozism. Such a charge, tantamount to atheism, was vigorously denied by Lessing’s friend Moses Mendelssohn, leading to a bitter public dispute among partisans. The controversy gradually escalated into a debate about the values of the Enlightenment and the value of reason. Reinhold maintained in his letters that Kant’s Critique of Pure Reason could settle this dispute by defending the authority and bounds of reason. Reinhold’s letters were widely read and made Kant the most famous philosopher of his era.

Later work

Kant published a second edition of the Critique of Pure Reason in 1787, heavily revising the first parts of the book. Most of his subsequent work focused on other areas of philosophy. He continued to develop his moral philosophy, notably in 1788’s Critique of Practical Reason (known as the second Critique), and 1797’s Metaphysics of Morals. The 1790 Critique of the Power of Judgment (the third Critique) applied the Kantian system to aesthetics and teleology. In 1792, Kant’s attempt to publish the Second of the four Pieces of Religion within the Bounds of Bare Reason, in the journal Berlinische Monatsschrift, met with opposition from the King’s censorship commission, which had been established that same year in the context of the French Revolution. Kant then arranged to have all four pieces published as a book, routing it through the philosophy department at the University of Jena to avoid the need for theological censorship. This insubordination earned him a now-famous reprimand from the King. When he nevertheless published a second edition in 1794, the censor was so irate that he arranged for a royal order that required Kant never to publish or even speak publicly about religion. Kant then published his response to the King’s reprimand and explained himself in the preface of The Conflict of the Faculties.

He also wrote a number of semi-popular essays on history, religion, politics, and other topics. These works were well received by Kant’s contemporaries and confirmed his preeminent status in eighteenth-century philosophy. There were several journals devoted solely to defending and criticizing Kantian philosophy. Despite his success, philosophical trends were moving in another direction. Many of Kant’s most important disciples and followers (including Reinhold, Beck, and Fichte) transformed the Kantian position. The progressive stages of revision of Kant’s teachings marked the emergence of German idealism. Kant opposed these developments and publicly denounced Fichte in an open letter in 1799. It was one of his final acts expounding a stance on philosophical questions. In 1800, a student of Kant named Gottlob Benjamin Jäsche (1762–1842) published a manual of logic for teachers called Logik, which he had prepared at Kant’s request. Jäsche prepared the Logik using a copy of a textbook in logic by Georg Friedrich Meier entitled Excerpt from the Doctrine of Reason, in which Kant had written copious notes and annotations. The Logik has been considered of fundamental importance to Kant’s philosophy, and the understanding of it. The great 19th-century logician Charles Sanders Peirce remarked, in an incomplete review of Thomas Kingsmill Abbott’s English translation of the introduction to Logik, that “Kant’s whole philosophy turns upon his logic.” Also, Robert Schirokauer Hartman and Wolfgang Schwarz wrote in the translators’ introduction to their English translation of the Logik, “Its importance lies not only in its significance for the Critique of Pure Reason, the second part of which is a restatement of fundamental tenets of the Logic, but in its position within the whole of Kant’s work”.

Death and burial

Kant’s health, long poor, worsened. He died at Königsberg on 12 February 1804, uttering “Es ist gut” (It is good) before expiring. His unfinished final work was published as Opus Postumum. Kant always cut a curious figure in his lifetime for his modest, rigorously scheduled habits, which have been referred to as clocklike. However, Heinrich Heine noted the magnitude of “his destructive, world-crushing thoughts” and considered him a sort of philosophical “executioner”, comparing him to Robespierre with the observation that both men “represented in the highest the type of provincial bourgeois. Nature had destined them to weigh coffee and sugar, but Fate determined that they should weigh other things and placed on the scales of the one a king, on the scales of the other a god.” When his body was transferred to a new burial spot, his skull was measured during the exhumation and found to be larger than the average German male’s with a “high and broad” forehead. His forehead has been an object of interest ever since it became well known through his portraits: “In Döbler’s portrait and in Kiefer’s faithful if expressionistic reproduction of it – as well as in many of the other late eighteenth- and early nineteenth-century portraits of Kant – the forehead is remarkably large and decidedly retreating.”

Kant’s mausoleum adjoins the northeast corner of Königsberg Cathedral in Kaliningrad, Russia. The mausoleum was constructed by the architect Friedrich Lahrs and was finished in 1924, in time for the bicentenary of Kant’s birth. Originally, Kant was buried inside the cathedral, but in 1880 his remains were moved to a neo-Gothic chapel adjoining the northeast corner of the cathedral. Over the years, the chapel became dilapidated and was demolished to make way for the mausoleum, which was built on the same location.

The tomb and its mausoleum are among the few artifacts of German times preserved by the Soviets after they captured the city. Today, many newlyweds bring flowers to the mausoleum. Artifacts previously owned by Kant, known as Kantiana, were included in the Königsberg City Museum. However, the museum was destroyed during World War II. A replica of the statue of Kant that in German times stood in front of the main University of Königsberg building was donated by a German entity in the early 1990s and placed in the same grounds. After the expulsion of Königsberg’s German population at the end of World War II, the University of Königsberg where Kant taught was replaced by the Russian-language Kaliningrad State University, which appropriated the campus and surviving buildings. In 2005, the university was renamed Immanuel Kant State University of Russia. The name change was announced at a ceremony attended by President Vladimir Putin of Russia and Chancellor Gerhard Schröder of Germany, and the university formed a Kant Society, dedicated to the study of Kantianism. The university was again renamed in the 2010s, to Immanuel Kant Baltic Federal University.


Like many of his contemporaries, Kant was greatly impressed with the scientific advances made by Newton and others. This new evidence of the power of human reason, however, called into question the traditional authority of politics and religion. Although this was in some respects liberatory, it was in other respects threatening. In particular, the modern mechanistic view of the world called into question the very possibility of morality; for, if there is no agency, there cannot be any responsibility. The aim of Kant’s critical project is to secure human autonomy, the basis of religion and morality, from this threat of mechanism—and to do so in a way that preserves the advances of modern science.

In the Critique of Pure Reason, Kant summarizes his philosophical concerns in the following three questions:

What can I know?

What should I do?

What may I hope?

The Critique of Pure Reason focuses upon the first question and opens a conceptual space for an answer to the second question. It argues that even though we cannot, strictly know that we are free, we can – and for practical purposes, must – think of ourselves as free. In Kant’s own words, “I had to deny knowledge in order to make room for faith.” Our rational faith in morality is further developed in The Groundwork of the Metaphysics of Morals and The Critique of Practical Reason. The Critique of the Power of Judgment argues we may rationally hope for the harmonious unity of the theoretical and practical domains treated in the first two Critiques on the basis, not only of its conceptual possibility, but also on the basis of our affective experience of natural beauty and, more generally, the organization of the natural world. In Religion within the Bounds of Mere Reason, Kant endeavors to complete his answer to this third question. These works all place the active, rational human subject at the center of the cognitive and moral worlds. In brief, Kant argues that the mind itself necessarily makes a constitutive contribution to knowledge, that this contribution is transcendental rather than psychological, and that to act autonomously is to act according to rational moral principles.

Kant’s critical project

Kant’s 1781 (revised 1787) book the Critique of Pure Reason has often been cited as the most significant volume of metaphysics and epistemology in modern philosophy. In the first Critique, and later on in other works as well, Kant frames the “general” and “real problem of pure reason” in terms of the following question: “How are synthetic judgments a priori possible?”

To parse this claim, it is necessary to define some terms. First, Kant makes a distinction in terms of the source of the content of knowledge:

Cognitions a priori: “cognition independent of all experience and even of all the impressions of the senses”.

Cognitions a posteriori: cognitions that have their sources in experience—that is, which are empirical.

Second, he makes a distinction in terms of the form of knowledge: Analytic proposition: a proposition whose predicate concept is contained in its subject concept; e.g., “All bachelors are unmarried”, or “All bodies take up space”. These can also be called “judgments of clarification”. Synthetic proposition: a proposition whose predicate concept is not contained in its subject concept; e.g., “All bachelors are alone”, or “All bodies have weight”. These can also be called “judgments of amplification”.

An analytic proposition is true by nature of strictly conceptual relations. All analytic propositions are a priori (it is analytically true that no analytic proposition could be a posteriori). By contrast, a synthetic proposition is one the content of which includes something new. The truth or falsehood of a synthetic statement depends upon something more than what is contained in its concepts. The most obvious form of synthetic proposition is a simple empirical observation. Philosophers such as David Hume believed that these were the only possible kinds of human reason and investigation, which he called “relations of ideas” and “matters of fact”. Establishing the synthetic a priori as a third mode of knowledge would allow Kant to push back against Hume’s skepticism about such matters as causation and metaphysical knowledge more generally. This is because, unlike a posteriori cognition, a priori cognition has “true or strict…universality” and includes a claim of “necessity”. Kant himself regards it as uncontroversial that we do have synthetic a priori knowledge—most obviously, that of mathematics. That 7 + 5 = 12, he claims, is a result not contained in the concepts of seven, five, and the addition operation. Yet, although he considers the possibility of such knowledge to be obvious, Kant nevertheless assumes the burden of providing a philosophical proof that we have a priori knowledge in mathematics, the natural sciences, and metaphysics. It is the twofold aim of the Critique both to prove and to explain the possibility of this knowledge.

Before turning to Kant’s arguments in the body of the Critique, there are two more distinctions from its introductory sections that must be introduced. “There are”, Kant says, “two stems of human cognition, which may perhaps arise from a common but to us unknown root, namely sensibility and understanding, through the first of which objects are given to us, but through the second of which they are thought.” Kant’s term for the object of sensibility is intuition, and his term for the object of the understanding is concept. In general terms, the former is a non-discursive representation of a particular object, and the latter is a discursive (or mediate) representation of a general type of object. The conditions of possible experience require both intuitions and concepts, that is, the affection of the receptive sensibility and the actively synthesizing power of the understanding. Thus the statement: “Thoughts without content are empty, intuitions without concepts are blind.” Kant’s basic strategy in the first half of his book will be to argue that some intuitions and concepts are pure—that is, are contributed entirely by the mind, independent of anything empirical. Knowledge generated on this basis, under certain conditions, can be synthetic a priori. This insight is known as Kant’s “Copernican revolution”, because, just as Copernicus advanced astronomy by way of a radical shift in perspective, so Kant here claims do the same for metaphysics. The second half of the Critique is the explicitly critical part. In this “transcendental dialectic”, Kant argues that many of the claims of traditional rationalist metaphysics violate the criteria he claims to establishing the first, “constructive” part of his book. As Kant observes, “human reason, without being moved by the mere vanity of knowing it all, inexorably pushes on, driven by its own need to such questions that cannot be answered by any experiential use of reason”. It is the project of “the critique of pure reason” to establish the limits as to just how far reason may legitimately so proceed.

The doctrine of transcendental idealism

The section of the Critique entitled “The transcendental aesthetic” advances Kant’s famous thesis of transcendental idealism. Something is “transcendental” if it is a necessary condition for the possibility of experience, and “idealism” denotes some form of mind-dependence that must be further specified. (The correct interpretation of Kant’s own specification remains controversial). The thesis, then, states that human beings only experience and know appearances, not things-in-themselves, because space and time are nothing but the subjective forms of intuition that we ourselves contribute to experience. Nevertheless, although Kant says that space and time are “transcendentally ideal” – the pure forms of human sensibility, rather than part of nature or reality as it exists in-itself – he also claims that they are “empirically real”, by which he means “that ‘everything that can come before us externally as an object’ is in both space and time, and that our internal intuitions of ourselves are in time”. However, we may interpret Kant’s doctrine, he clearly wishes to distinguish his position from the subjective idealism of Berkeley. Paul Guyer, although critical of many of Kant’s arguments in this section, nevertheless writes of the “Transcendental Aesthetic” that it “not only lays the first stone in Kant’s constructive theory of knowledge; it also lays the foundation for both his critique and his reconstruction of traditional metaphysics. It argues that all genuine knowledge requires a sensory component, and thus that metaphysical claims that transcend the possibility of sensory confirmation can never amount to knowledge”.

Interpretive disagreements

One interpretation, known as the “two-world” interpretation, regards Kant’s position as a statement of epistemological limitation, that we are not able to transcend the bounds of our own mind, meaning that we cannot access the “thing-in-itself”. However, Kant also speaks of the thing in itself or transcendent object as a product of the (human) understanding as it attempts to conceive of objects in abstraction from the conditions of sensibility. Following this line of thought, some interpreters have argued that the thing in itself does not represent a separate ontological domain but simply a way of considering objects by means of the understanding alone; this is known as the “two-aspect” view.

Kant’s theory of judgment

Following the “Transcendental Analytic” is the “Transcendental Logic”. Whereas the former was concerned with the contributions of the sensibility, the latter is concerned, first, with the contributions of the understanding (“Transcendental Analytic”) and, second, with the faculty of reason as the source of both metaphysical errors and genuine regulatory principles (“Transcendental Dialectic”). The “Transcendental Analytic” is further divided into two sections. The first, “Analytic of Concepts”, is concerned with establishing the universality and necessity of the pure concepts of the understanding (i.e., the categories). This section contains Kant’s famous “transcendental deduction”. The second, “Analytic of Principles”, is concerned with the application of those pure concepts in empirical judgments. This second section is longer than the first and is further divided into many sub-sections.

Transcendental deduction of the categories of the understanding

The “Analytic of Concepts” argues for the universal and necessary validity of the pure concepts of the understanding, or the categories, e.g., the concepts of substance and causation. These twelve basic categories define what it is to be a thing in general—that is, they articulate the necessary conditions according to which something is a possible object of experience. These, in conjunction with the a priori forms of intuition, are the basis of all synthetic a priori cognition. According to Guyer and Wood, “Kant’s idea is that just as there are certain essential features of all judgments, so there must be certain corresponding ways in which we form the concepts of objects so that judgments may be about objects”. Kant provides two central lines of argumentation in support of his claims about the categories. The first, known as the “metaphysical deduction”, proceeds analytically from a table of the Aristotelian logical functions of judgment. As Kant was aware, however, this assumes precisely what the skeptic rejects, namely, the existence of synthetic a priori cognition. For this reason, Kant also supplies a synthetic argument that does not depend upon the assumption in dispute.

This argument, provided under the heading “Transcendental Deduction of the Pure Concepts of the Understanding”, is widely considered to be both the most important and the most difficult of Kant’s arguments in the Critique. Kant himself said that it is the one that cost him the most labor. Frustrated by its confused reception in the first edition of his book, he rewrote it entirely for the second edition. The “Transcendental Deduction” gives Kant’s argument that these pure concepts apply universally and necessarily to the objects that are given in experience. According to Guyer and Wood, “He centers his argument on the premise that our experience can be ascribed to a single identical subject, via what he calls the ‘transcendental unity of apperception,’ only if the elements of experience given in intuition are synthetically combined so as to present us with objects that are thought through the categories”. Kant’s principle of apperception is that “The I think must be able to accompany all my representations; for otherwise something would be represented in me that could not be thought at all, which is as much as to say that the representation would either be impossible or else at least would be nothing for me.” The necessary possibility of the self-ascription of the representations of self-consciousness, identical to itself through time, is an a priori conceptual truth that cannot be based on experience. This, however, is only a bare sketch of one of the arguments that Kant presents.

Principles of pure understanding

Kant’s deduction of the categories in the “Analytic of Concepts”, if successful, demonstrates its claims about the categories only in an abstract way. The task of the “Analytic of Principles” is to show both that they must universally apply to objects given in actual experience (i.e., manifolds of intuition) and how it is they do so. In the first book of this section on the “schematism”, Kant connects each of the purely logical categories of the understanding to the temporality of intuition to show that, although non-empirical, they do have purchase upon the objects of experience. The second book continues this line of argument in four chapters, each associated with one of the category groupings. In some cases, it adds a connection to the spatial dimension of intuition to the categories it analyzes. The fourth chapter of this section, “The Analogies of Experience”, marks a shift from “mathematical” to “dynamical” principles, that is, to those that deal with relations among objects. Some commentators consider this the most significant section of the Critique. The analogies are three in number:

Principle of persistence of substance: Kant is here concerned with the general conditions of determining time-relations among the objects of experience. He argues that the unity of time implies that “all change must consist in the alteration of states in an underlying substance, whose existence and quantity must be unchangeable or conserved”.

Principle of temporal succession according to the law of causality: Here Kant argues that “we can make determinate judgments about the objective succession of events, as contrasted to merely subjective successions of representations, only if every objective alteration follows a necessary rule of succession, or a causal law.” This is Kant’s most direct rejoinder to Hume’s skepticism about causality.

Principle of simultaneity according to the law of reciprocity or community: The final analogy argues that “determinate judgments that objects (or states of substance) in different regions of space exists simultaneously are possible only if such objects stand in mutual causal relation of community or reciprocal interaction.” (This is Kant’s rejoinder to Leibniz’s thesis in the Monadology.)

The fourth section of this chapter, which is not an analogy, deals with the empirical use of the modal categories. That was the end of the chapter in the A edition of the Critique.

The B edition, however, includes one more short section, “The Refutation of Idealism”. In this section, by analysis of the concept of self-consciousness, Kant argues that his transcendental idealism is a “critical” or “formal” idealism that does not deny the existence of reality apart from our subjective representations. The final chapter of “The Analytic of Principles” distinguishes phenomena, of which we have can have genuine knowledge, from noumena, a term which refers to objects of pure thought that we cannot know, but to which we may still refer “in a negative sense”. An Appendix to the section further develops Kant’s criticism of Leibnizian-Wolffian rationalism by arguing that its “dogmatic” metaphysics confuses the “mere features of concepts through which we think things…[with] features of the objects themselves”. Against this, Kant reasserts his own insistence upon the necessity of a sensible component in all genuine knowledge.

Critique of metaphysics

The second of the two Divisions of “The Transcendental Logic”, “The Transcendental Dialectic”, contains the “negative” portion of Kant’s Critique, which builds upon the “positive” arguments of the preceding “Transcendental Analytic” to expose the limits of metaphysical speculation. In particular, it is concerned to demonstrate as spurious the efforts of reason to arrive at knowledge independent of sensibility. This endeavor, Kant argues, is doomed to failure, which he claims to demonstrate by showing that reason, unbounded by sense, is always capable of generating opposing or otherwise incompatible conclusions. Like “the light dove, in free flight cutting through the air, the resistance of which it feels”, reason “could get the idea that it could do even better in airless space”. Against this, Kant claims that, absent epistemic friction, there can be no knowledge. Nevertheless, Kant’s critique is not entirely destructive. He presents the speculative excesses of traditional metaphysics as inherent in our very capacity of reason. Moreover, he argues that its products are not without some (carefully qualified) regulative value.

On the concepts of pure reason

Kant calls the basic concepts of metaphysics “ideas”. They are different from the concepts of understanding in that they are not limited by the stricture of possible experience. “Transcendental illusion” is Kant’s term for the tendency of reason to produce such ideas. Although reason has a “logical use” of simply drawing inferences from principles, in “The Transcendental Dialectic”, Kant is concerned with its purportedly “real use” to arrive at conclusions by way of unchecked regressive syllogistic ratiocination. The three categories of relation, pursued without regard to the limits of possible experience, yield the three central ideas of traditional metaphysics:

The soul: the concept of substance as the ultimate subject;

The world in its entirety: the concept of causation as a completed series; and

God: the concept of community as the common ground of all possibilities.

Although Kant denies that these ideas can be objects of genuine cognition, he argues that they are the result of reason’s inherent drive to unify cognition into a systematic whole.

Leibnizian-Wolffian metaphysics was divided into four parts: ontology, psychology, cosmology, and theology. Kant replaces the first with the positive results of the first part of the Critique. He proposes to replace the following three with his later doctrines of anthropology, the metaphysical foundations of natural science, and the critical postulation of human freedom and morality.

The dialectical inferences of pure reason

In the second of the two Books of “The Transcendental Dialectic”, Kant undertakes to demonstrate the contradictory nature of unbounded reason. He does this by developing contradictions in each of the three metaphysical disciplines that he contends are, in fact, pseudo-sciences. This section of the Critique is long and Kant’s arguments are extremely detailed. In this context, it not possible to do much more than enumerate the topics of discussion. The first chapter addresses what Kant terms the paralogisms—i.e., false inferences—that pure reason makes in the metaphysical discipline of rational psychology. He argues that one cannot take the mere thought of “I” in the proposition “I think” as the proper cognition of “I” as an object. In this way, he claims to debunk various metaphysical theses about the substantiality, unity, and self-identity of the soul.

The second chapter, which is the longest, takes up the topic Kant calls the antinomies of pure reason—that is, the contradictions of reason with itself—in the metaphysical discipline of rational cosmology. (Originally, Kant had thought that all transcendental illusion could be analyzed in antinomic terms) He presents four cases in which he claims reason is able to prove opposing theses with equal plausibility:

That “reason seems to be able to prove that the universe is both finite and infinite in space and time”;

that “reason seems to be able to prove that matter both is and is not infinitely divisible into ever smaller parts”;

that “reason seems to be able to prove that free will cannot be a causally efficacious part of the world (because all of nature is deterministic) and yet that it must be such a cause”; and,

that “reason seems to be able to prove that there is and there is not a necessary being (which some would identify with God)”. Kant further argues in each case that his doctrine of transcendental idealism is able to resolve the antinomy. The third chapter examines fallacious arguments about God in rational theology under the heading of the “Ideal of Pure Reason”. (Whereas an idea is a pure concept generated by reason, an ideal is the concept of an idea as an individual thing) Here Kant addresses and claims to refute three traditional arguments for the existence of God: the ontological argument, the cosmological argument, and the physio-theological argument (i.e., the argument from design). The results of the transcendental dialectic so far appear to be entirely negative. In an Appendix to this section, however, Kant rejects such a conclusion. The ideas of pure reason, he argues, have an important regulatory function in directing and organizing our theoretical and practical inquiry. Kant’s later works elaborate upon this function at length and in detail.

Moral thought

Kant developed his ethics, or moral philosophy, in three works: Groundwork of the Metaphysics of Morals (1785), Critique of Practical Reason (1788), and Metaphysics of Morals (1797). With regard to morality, Kant argued that the source of the good lies not in anything outside the human subject, either in nature or given by God, but rather is only the good will itself. A good will is one that acts from duty in accordance with the universal moral law that the autonomous human being freely gives itself. This law obliges one to treat humanity—understood as rational agency, and represented through oneself as well as others—as an end in itself rather than (merely) as means to other ends the individual might hold. Kant is known for his theory that all moral obligation is grounded in what he calls the “categorical imperative”, which is derived from the concept of duty. He argues that the moral law is a principle of reason itself, not based on contingent facts about the world, such as what would make us happy; to act on the moral law has no other motive than “worthiness to be happy”.

The categorical imperative

In his Groundwork, Immanuel Kant introduced the categorical imperative: “Act only in accordance with that maxim through which you at the same time can will that it become a universal law.”

Kant makes a distinction between categorical and hypothetical imperatives. A hypothetical imperative is one that we must obey to satisfy contingent desires. A categorical imperative binds us regardless of our desires: for example, everyone has a duty to not lie, regardless of circumstances, even though it is sometimes in our narrowly selfish interest to do so. These imperatives are morally binding because they are based on reason, rather than contingent facts about an agent. Unlike hypothetical imperatives, which bind us insofar as we are part of a group or society which we owe duties to, we cannot opt out of the categorical imperative, because we cannot opt out of being rational agents. We owe a duty to rationality by virtue of being rational agents; therefore, rational moral principles apply to all rational agents at all times. Stated in other terms, with all forms of instrumental rationality excluded from morality, “the moral law itself, Kant holds, can only be the form of lawfulness itself, because nothing else is left once all content has been rejected”.

Political philosophy

In Towards Perpetual Peace: A Philosophical Project, Kant listed several conditions that he thought necessary for ending wars and creating a lasting peace. They included a world of constitutional republics. His classical republican theory was extended in the Doctrine of Right, the first part of the Metaphysics of Morals (1797). Kant believed that universal history leads to the ultimate world of republican states at peace, but his theory was not pragmatic. The process was described in Perpetual Peace as natural rather than rational: What affords this guarantee (surety) is nothing less than the great artist nature (natura daedala rerum) from whose mechanical course purposiveness shines forth visibly, letting concord arise by means of the discord between human beings even against their will; and for this reason nature, regarded as necessitation by a cause the laws of whose operation are unknown to us, is called fate, but if we consider its purposiveness in the course of the world as the profound wisdom of a higher cause directed to the objective final end of the human race and predetermining this course of the world, it is called providence. Kant’s political thought can be summarized as republican government and international organization: “In more characteristically Kantian terms, it is doctrine of the state based upon the law (Rechtsstaat) and of eternal peace. Indeed, in each of these formulations, both terms express the same idea: that of legal constitution or of ‘peace through law”. “Kant’s political philosophy, being essentially a legal doctrine, rejects by definition the opposition between moral education and the play of passions as alternate foundations for social life. The state is defined as the union of men under law. The state rightly so called is constituted by laws which are necessary a priori because they flow from the very concept of law. A regime can be judged by no other criteria nor be assigned any other functions, then those proper to the lawful order as such”.

He opposed “democracy”, which at his time meant direct democracy, believing that majority rule posed a threat to individual liberty. He stated, “democracy in the strict sense of the word is necessarily a despotism because it establishes an executive power in which all decide for and, if need be, against one (who thus does not agree), so that all, who are nevertheless not all, decide; and this is a contradiction of the general will with itself and with freedom.” As with most writers at the time, he distinguished three forms of government—namely, democracy, aristocracy, and monarchy—with mixed government as the most ideal form of it. Although Kant published this as a “popular piece”, Mary J. Gregor points out that two years later, in The Metaphysics of Morals, Kant claims to demonstrate systematically that “establishing universal and lasting peace constitutes not merely a part of the doctrine of right, but rather the entire final end of the doctrine of right within the limits of mere reason”. The Doctrine of Right, published in 1797, contains Kant’s most mature and systematic contribution to political philosophy. It addresses duties according to law, which are “concerned only with protecting the external freedom of individuals” and indifferent to incentives. (Although we do have a moral duty “to limit ourselves to actions that are right, that duty is not part of [right] itself”.) Its basic political idea is that “each person’s entitlement to be his or her own master is only consistent with the entitlements of others if public legal institutions are in place”.