Immanuel Kant

Early life

Immanuel Kant was born on 22 April 1724 into a Prussian German family of Lutheran faith in Königsberg in East Prussia (now Kaliningrad Oblast, Russia). His mother, Anna Regina Reuter, was born in Königsberg to a father from Nuremberg. Her surname is sometimes erroneously given as Porter. Kant's father, Johann Georg Kant, was a German harness-maker from Memel, at the time Prussia's most northeastern city (now Klaipėda, Lithuania). Kant believed his family to be of Scottish descent and that his paternal grandfather's name was originally "Cant", although this has not been verified by genealogical research.

Kant was baptized as Emanuel, changing 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. Immanuel Kant's early education was strict, punitive, and highly disciplinary, with an emphasis on Latin and religious instruction rather than mathematics and science.

In his later years, Kant lived a strictly ordered life. It was said that neighbors would set their watches by his daily walks. Kant considered marriage twice, first to a widow and then to a Westphalian woman, but on both occasions waited too long. Although he never married, he nevertheless had a rewarding social life; he was a popular teacher and a modestly successful author, even before commencing his major philosophical works.

Young scholar

Kant demonstrated an early aptitude for study. He first attended the Collegium Fridericianum (then directed by Franz Albert Schultz), 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 would later remain for the rest of his professional life. He studied the philosophy of Gottfried Leibniz and Christian Wolff under Martin Knutzen (Associate Professor of Logic and Metaphysics from 1734 until he died 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 negatively. 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 main publisher, Johann Friedrich Hartknoch, was also a Freemason.

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).

During the Russian occupation of Königsberg during the Seven Years' War (1758–1762), Kant's financial circumstances improved, as he obtained a number of well-paid tutoring assignments from Russian military officers and civil administrators stationed in the city. In December 1758, after the death of Johann David Kypke, Kant petitioned Empress Elizabeth for appointment to the vacant chair of logic and metaphysics at the University of Königsberg, but the position was awarded to another candidate.

Early work

Kant is best known for his work in the philosophy of ethics and metaphysics, but he also contributed significantly to other disciplines. In 1754, while contemplating a prize question by the Berlin Academy about the problem of Earth's rotation, he argued that the Moon's gravity would slow down the Earth's spin. 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 at 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 ("New Remarks toward an Elucidation of the Theory of Winds"), Kant laid out a qualitative insight into what is now called 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 had 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 devoted his efforts increasingly towards philosophical issues, even though he continued to write on the sciences throughout his life. In the early 1760s, he 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.

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 people know the mind only 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, printed by Johann Friedrich Hartknoch. 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. Perhaps the most direct contested matter was Hume's argument against any necessary connection between causal events, which Hume characterized as the "cement of the universe". In the Critique of Pure Reason, Kant argues for what he takes to be the a priori justification of such necessary connection.

Although now recognized as one of the greatest works in the history of philosophy, the 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 by itself instead of considering the process of reasoning within the context of language and one's entire personality. Similarly to Christian Garve and Johann Georg Heinrich Feder, he rejected Kant's position that space and time possess a form that can be analyzed. Garve and Feder also faulted the 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.

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 (1798).

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 Karl Leonhard Reinhold, Jakob Sigismund Beck, and Johann Gottlieb Fichte) transformed the Kantian position. The progressive stages of revision of Kant's teachings marked the emergence of German idealism. In what was one of his final acts expounding a stance on philosophical questions, Kant opposed these developments and publicly denounced Fichte in an open letter in 1799.

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 S. 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 in Königsberg on 12 February 1804, uttering Es ist gut ("It is good") before his death. 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. Heinrich Heine observed the magnitude of "his destructive, world-crushing thoughts" and considered him a sort of philosophical "executioner", comparing him to Maximilien 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.

Into the 21st century, 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, which was considered a politically-charged issue due to the residents having mixed feelings about its German past, was announced at a ceremony attended by Russian president Vladimir Putin and German chancellor Gerhard Schröder, and the university formed a Kant Society, dedicated to the study of Kantianism. In 2010, the university was again renamed to Immanuel Kant Baltic Federal University.

Philosophy

Like many of his contemporaries, Kant was greatly impressed with the scientific advances made by Sir Isaac Newton and others. This new evidence of the power of human reason called into question for many the traditional authority of politics and religion. 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." Kant's moral philosophy is further developed in the Groundwork of the Metaphysics of Morals, 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 of our affective experience of natural beauty and, more generally, the teleological organization of the natural world. In Religion within the Bounds of Mere Reason, Kant endeavors to complete his answer to this third question by arguing for a rationalist form of religion grounded on our practical (i.e., moral) lives.

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) 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 in later 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 understand this claim, it is necessary to define some terms. First, Kant makes a distinction between two sources 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 between two kinds of judgements:

Analytic judgements: judgements in which the predicate concept is contained in the subject concept; e.g., "All bachelors are unmarried", or "All bodies are extended". These can also be called "judgments of clarification".

Synthetic judgements: judgements in which the predicate concept is not contained in the subject concept; e.g., "Some bachelors are alone", "All swans are white", or "All bodies have weight". These can also be called "judgments of amplification".

All analytic judgements are a priori since experience is not necessary for analyzing the content of a concept we already possess. By contrast, a synthetic judgement is one whose predicate concept contains something not in the subject concept. The most obvious examples of synthetic judgement are judgments grounded in empirical observations. The two kinds of knowledge and two kinds of judgment yield a fourfold table:

Kant believed that previous philosophers had neglected synthetic a priori judgments, and had paid attention only to analytic a priori and synthetic a posteriori judgments. David Hume, for example, believed that all knowledge is either of "relations of ideas" (which are analytic a priori) or "matters of fact" (which are synthetic a posteriori). Hume's taxonomy excludes the synthetic a priori. But by establishing the synthetic a priori as a third kind of judgment, Kant believes we can push back against Hume's skepticism about such matters as causation and metaphysical knowledge more generally. This is because, unlike merely a posteriori judgments, a priori judgments have "true or strict ... universality" and includes a claim of "necessity". And, unlike merely analytic claims, synthetic judgements extend our knowledge beyond the subject concept. This means that showing how synthetic a priori judgments are possible amounts to showing how substantive knowledge about necessary features of the world is possible.

Doctrine of transcendental idealism

In the section of the Critique entitled "The Transcendental Aesthetic", Kant argues for the doctrine of transcendental idealism. The doctrine is "transcendental" because it explains a necessary condition for the possibility of experience and is a form of "idealism" because those conditions are dependent on features of the mind. The details of the correct interpretation of transcendental idealism are controversial, but there is broad agreement on two basic theses. First, space and time are not things in themselves but are mere forms of intuition (space is the form of outer intuition, and time is the form of inner intuition). Second, we have knowledge only of appearances and not of things in themselves. The second thesis, Kant believes, follows from the first: because our a priori forms of intuition are necessary conditions of the possibility of experience, anything that fall outside what our sensible faculty can receive are unknowable. 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 is 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 Kant's doctrine is interpreted, he wished to distinguish his position from the subjective idealism of George Berkeley.

Paul Guyer, although critical of many of Kant's arguments in this section, 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."

One interpretation, known as the "two-aspect" (or "one-world") interpretation, takes transcendental idealism to be, most fundamentally, an epistemological thesis. On this reading of Kant, popularized especially by Henry E. Allison, the thing-in-itself and the phenomenal appearance are the same object, and transcendental idealism is a thesis about what is necessary for finite, discursive minds to consider objects as they are given to us by sensibility. Some commentators, while agreeing that there is just one set of objects, take transcendental idealism to be a thesis about the properties of those objects, some of which we have access to, and others of which are unknowable to us.

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.

The "Analytic of Concepts" argues for the universal and necessary validity of the pure concepts of the understanding, or the categories, for instance, 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 Paul Guyer and Allen W. 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, 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.

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.

Kant calls the basic concepts of metaphysics "ideas". They are different from the concepts of understanding in that they are not limited by the critical stricture limiting knowledge to the conditions of possible experience and its objects. "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.

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".

Nevertheless, experts largely agree that Kant's ethics predate in most of its central ideas the critical period.

In the Critique of Pure Reason, Kant distinguishes between the transcendental idea of freedom, which as a psychological concept is "mainly empirical" and refers to "whether a faculty of beginning a series of successive things or states from itself is to be assumed", and the practical concept of freedom as the independence of our will from the "coercion" or "necessitation through sensuous impulses". Kant finds it a source of difficulty that the practical idea of freedom is founded on the transcendental idea of freedom, but for the sake of practical interests uses the practical meaning, taking "no account of ... its transcendental meaning", which he feels was properly "disposed of" in the Third Antinomy, and as an element in the question of the freedom of the will is for philosophy "a real stumbling block" that has embarrassed speculative reason.

Kant calls practical "everything that is possible through freedom"; he calls the pure practical laws that are never given through sensuous conditions, but are held analogously with the universal law of causality, moral laws. Reason can give us only the "pragmatic laws of free action through the senses", but pure practical laws given by reason a priori dictate "what is to be done". Kant's categories of freedom function primarily as conditions for the possibility for actions (i) to be free, (ii) to be understood as free, and (iii) to be morally evaluated. For Kant, although actions as theoretical objects are constituted by means of the theoretical categories, actions as practical objects (objects of practical use of reason, and which can be good or bad) are constituted by means of the categories of freedom. Only in this way can actions, as phenomena, be a consequence of freedom, and be understood and evaluated as such.

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 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, than those proper to the lawful order as such."

Kant opposed "democracy", which at his time meant direct democracy, believing that majority rule posed a threat to individual liberty. He stated that "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."

Religious writings

Starting in the 20th century, commentators tended to see Kant as having a strained relationship with religion, although in the nineteenth century this had not been the prevalent view. Karl Leonhard Reinhold, whose letters helped make Kant famous, wrote: "I believe that I may infer without reservation that the interest of religion, and of Christianity in particular, accords completely with the result of the Critique of Reason." According to Johann Friedrich Schultz, who wrote one of the first commentaries on Kant: "And does not this system itself cohere most splendidly with the Christian religion? Do not the divinity and beneficence of the latter become all the more evident?" The reason for these views was Kant's moral theology and the widespread belief that his philosophy was the great antithesis to Spinozism, which was widely seen as a form of sophisticated pantheism or even atheism. As Kant's philosophy disregarded the possibility of arguing for God through pure reason alone, for the same reasons it also disregarded the possibility of arguing against God through pure reason alone.

Kant directs his strongest criticisms of the organization and practices of religious organizations at those that encourage what he sees as a religion of counterfeit service to God. Among the major targets of his criticism are external ritual, superstition, and a hierarchical church order. He sees these as efforts to make oneself pleasing to God in ways other than conscientious adherence to the principle of moral rightness in choosing and acting upon one's maxims. Kant's criticisms on these matters, along with his rejection of certain theoretical proofs for the existence of God that were grounded in pure reason (particularly the ontological argument) and his philosophical commentary on some Christian doctrines, have resulted in interpretations that see Kant as hostile to religion in general and to Christianity in particular. Other interpreters, nevertheless, consider that Kant was trying to mark off defensible from indefensible Christian belief.

Regarding Kant's conception of religion, some critics have argued that he was sympathetic to deism. Other critics have argued that Kant's moral conception moves from deism to theism (as moral theism), for example Allen W. Wood, as well as Merold Westphal. As for Kant's book Religion within the Bounds of Mere Reason, it was emphasized that Kant reduced religiosity to rationality, religion to morality, and Christianity to ethics; however, many interpreters, including Wood, alongside Lawrence Pasternack, now agree with Stephen Palmquist's claim that a better way of reading Kant's Religion is to see him as raising morality to the status of religion.

Aesthetics

Kant discusses the subjective nature of aesthetic qualities and experiences in Observations on the Feeling of the Beautiful and Sublime (1764). Kant's contribution to aesthetic theory is developed in the Critique of the Power of Judgment (1790), where he investigates the possibility and logical status of "judgments of taste". In the "Critique of Aesthetic Judgment", the first major division of the Critique of the Power of Judgment, Kant used the term "aesthetic" in a manner that resembles its modern sense. In the Critique of Pure Reason, to note essential differences between judgments of taste, moral judgments, and scientific judgments, Kant abandoned the term "aesthetic" as "designating the critique of taste", noting that judgments of taste could never be "directed" by "laws a priori". After Alexander Gottlieb Baumgarten, who wrote Aesthetica (1750–58), Kant was one of the first philosophers to develop and integrate aesthetic theory into a unified and comprehensive philosophical system, utilizing ideas that played an integral role throughout his philosophy. In the chapter "Analytic of the Beautiful" in the Critique of the Power of Judgment, Kant states that beauty is not a property of an artwork or natural phenomenon, but is instead consciousness of the pleasure that attends the 'free play' of the imagination and the understanding. Even though it appears that we are using reason to decide what is beautiful, the judgment is not a cognitive judgment, "and is consequently not logical, but aesthetical".

A pure judgement of taste is subjective since it refers to the emotional response of the subject and is based upon nothing but esteem for an object itself: it is a disinterested pleasure, and we feel that pure judgements of taste (i.e., judgements of beauty), lay claim to universal validity. This universal validity is not derived from a determinate concept of beauty but from common sense. Kant also believed that a judgment of taste shares characteristics with a moral judgment: both are disinterested, and we hold them to be universal. In the chapter "Analytic of the Sublime," Kant identifies the sublime as an aesthetic quality that, like beauty, is subjective, but unlike beauty, it refers to an indeterminate relationship between the faculties of the imagination and reason. It also shares the character of moral judgments in its engagement with reason. The feeling of the sublime, divided into two distinct modes (the mathematical and the dynamical sublime), describes two subjective moments that concern the relationship of the faculty of the imagination to reason. Some commentators argue that Kant's critical philosophy contains a third kind of the sublime, the moral sublime, which is the aesthetic response to the moral law or a representation, and a development of the "noble" sublime in Kant's theory of 1764.

Anthropology

Kant lectured on anthropology, the study of human nature, for twenty-three years. His Anthropology from a Pragmatic Point of View was published in 1798. Transcripts of Kant's lectures on anthropology were published for the first time in 1997 in German. Kant was among the first people of his time to introduce anthropology as an intellectual area of study, long before the field gained popularity, and his texts are considered to have advanced the field. His point of view was to influence the works of later philosophers such as Martin Heidegger and Paul Ricœur.

Kant was the first to suggest using a dimensionality approach to human diversity. He analyzed the nature of the Hippocrates-Galen four temperaments and plotted in two dimensions "what belongs to a human being's faculty of desire":

"his natural aptitude or natural predisposition" and "his temperament or sensibility". Cholerics were described as emotional and energetic, phlegmatics as balanced and weak, sanguines as balanced and energetic, and melancholics as emotional and weak. These two dimensions reappeared in all subsequent models of temperament and personality traits. Kant viewed anthropology in two broad categories: (1) the physiological approach, which he referred to as "what nature makes of the human being"; and (2) the pragmatic approach, which explores the things that a human "can and should make of himself".

Kant's theory of race and his prejudicial beliefs are among the most contentious areas of recent Kant scholarship. While few, if any, dispute the overt racism and chauvinism present in his work, a more contested question is the degree to which it degrades or invalidates his other contributions. His most severe critics assert that Kant intentionally manipulated science to support chattel slavery and discrimination. Others acknowledge that he lived in an era of immature science, with many erroneous beliefs, some racist, all appearing decades before evolution, molecular genetics, and other sciences that today are taken for granted. Kant was one of the most notable Enlightenment thinkers to defend racism. The philosopher Charles W. Mills is unequivocal: "Kant is also seen as one of the central figures in the birth of modern 'scientific' racism. Whereas other contributors to early racial thought like Carolus Linnaeus and Johann Friedrich Blumenbach had offered only 'empirical' (scare-quotes necessary!) observation, Kant produced a full-blown theory of race."

Influence and legacy

Kant's influence on Western thought has been profound. Although the basic tenets of Kant's transcendental idealism (i.e., that space and time are a priori forms of human perception rather than real properties and the claim that formal logic and transcendental logic coincide) have been claimed to be falsified by modern science and logic, and no longer set the intellectual agenda of contemporary philosophers, Kant is credited with having innovated the way philosophical inquiry has been carried on at least up to the early nineteenth century. This shift consisted of several closely related innovations that, although highly contentious in themselves, have become important in subsequent philosophy and in the social sciences broadly construed:

The human subject seen as the center of inquiry into human knowledge, such that it is impossible to philosophize about things as they exist independently of human perception or of how they are "for us";

the notion that is possible to discover and systematically explore the inherent limits of the human ability to know entirely a priori;

the notion of the "categorical imperative", an assertion that people are naturally endowed with the ability and obligation toward right reason and acting. Perhaps his most famous quote is drawn from the Critique of Practical Reason: "Two things fill my mind with ever new and increasing admiration and reverence ... : the starry heavens above me and the moral law within me";

the concept of "conditions of possibility", as in his notion of "the conditions of possible experience"; that is, that things, knowledge, and forms of consciousness rest on prior conditions that make them possible, so that, to understand or to know them, several conditions must be understood:

the claim that objective experience is actively constituted or constructed by the functioning of the human mind;

the concept of moral autonomy as central to humanity; and

the assertion of the principle that human beings should be treated as ends rather than as mere means.

Historical influence

During his own life, much critical attention was paid to Kant's thought. He influenced Reinhold, Fichte, Schelling, Hegel, and Novalis during the 1780s and 1790s. Samuel Taylor Coleridge was greatly influenced by Kant and helped to spread awareness of him, and of German Idealism generally, in the UK and the US. In his Biographia Literaria (1817), he credits Kant's ideas in coming to believe that the mind is not a passive, but an active agent in the apprehension of reality. Hegel was one of Kant's first major critics. In Hegel's view the entire project of setting a "transcendental subject" (i.e., human consciousness) apart from the living individual as well as from nature, history, and society was fundamentally flawed, although parts of that very project could be put to good use in a new direction. Similar concerns motivated Hegel's criticisms of Kant's concept of moral autonomy, to which Hegel opposed an ethic focused on the "ethical life" of the community. In a sense, Hegel's notion of "ethical life" is meant to subsume, rather than replace, Kantian ethics. And Hegel can be seen as trying to defend Kant's idea of freedom as going beyond finite "desires", by means of reason. Thus, in contrast to later critics like Nietzsche or Russell, Hegel shares some of Kant's concerns.

Kant's thinking on religion was used in Britain by philosophers such as Thomas Carlyle to challenge the nineteenth-century decline in religious faith. British Catholic writers, notably G. K. Chesterton and Hilaire Belloc, followed this approach. Criticisms of Kant were common in the realist views of the new positivism at that time. Arthur Schopenhauer was strongly influenced by Kant's transcendental idealism. Like Friedrich Heinrich Jacobi, Salomon Maimon, Gottlob Ernst Schulze, and Fichte before him, Schopenhauer was critical of Kant's theory of the thing-in-itself. Things-in-themselves, they argued, are neither the cause of what we observe, nor are they completely beyond our access. Ever since the Critique of Pure Reason, philosophers have been critical of Kant's theory of the thing-in-itself. Many have argued that, if such a thing exists beyond experience, then one cannot posit that it affects us causally, since that would entail stretching the category "causality" beyond the realm of experience.

With the success and wide influence of Hegel's writings, Kant's own influence began to wane, but a re-examination of his ideas began in Germany in 1865 with the publication of Kant und die Epigonen by Otto Liebmann, whose motto was "Back to Kant". There proceeded an important revival of Kant's theoretical philosophy, known as neo-Kantianism. Kant's notion of "critique" has been more broadly influential. The early German Romantics, especially Friedrich Schlegel in his "Athenaeum Fragments", used Kant's reflexive conception of criticism in their Romantic theory of poetry. Also in aesthetics, Clement Greenberg, in his classic essay "Modernist Painting", uses Kantian criticism, what Greenberg refers to as "immanent criticism", to justify the aims of abstract painting, a movement Greenberg saw as aware of the key limitation—flatness—that makes up the medium of painting. The French philosopher Michel Foucault was also greatly influenced by Kant's notion of "critique" and wrote several pieces on Kant for a re-thinking of the Enlightenment as a form of "critical thought". He went so far as to classify his own philosophy as a "critical history of modernity, rooted in Kant".

Influence on modern thinkers

With his Perpetual Peace, Kant is considered to have foreshadowed many of the ideas that have come to form the democratic peace theory, one of the main controversies in political science. More concretely, constructivist theorist Alexander Wendt proposed that the anarchy of the international system could evolve from the "brutish" Hobbesian anarchy understood by realist theorists, through Lockean anarchy, and ultimately a Kantian anarchy in which states would see their self-interests as inextricably linked to the well being of other states, thus transforming international politics into a far more peaceful form.

Prominent recent Kantians include the British philosophers P. F. Strawson, Onora O'Neill, and Quassim Cassam, and the American philosophers Wilfrid Sellars, Lewis White Beck and Christine Korsgaard. Due to the influence of Strawson and Sellars, among others, there has been a renewed interest in Kant's view of the mind. Central to many debates in philosophy of psychology and cognitive science is Kant's conception of the unity of consciousness.

Jürgen Habermas and John Rawls are two significant political and moral philosophers whose work is strongly influenced by Kant's moral philosophy. They have argued against relativism, supporting the Kantian view that universality is essential to any viable moral philosophy. Mou Zongsan's study of Kant has been cited as a highly crucial part in the development of Mou's personal philosophy, namely New Confucianism. Widely regarded as the most influential Kant scholar in China, Mou's rigorous critique of Kant's philosophy—having translated all three of Kant's critiques—served as an ardent attempt to reconcile Chinese and Western philosophy whilst increasing pressure to Westernize in China.

Because of the thoroughness of Kant's paradigm shift, his influence extends well beyond this to thinkers who neither specifically refer to his work nor use his terminology. Kant's influence extended to the social, behavioral, and physical sciences—as in the sociology of Max Weber, the psychology of Jean Piaget, and Carl Jung. Kant's work on mathematics and synthetic a priori knowledge is also cited by the theoretical physicist Albert Einstein as an early influence on his intellectual development, although it was one which he later criticized and rejected. In the 2020s, there was a renewed interest in Kant's theory of mind from the point of view of formal logic and computer science.