Immanuel Kant

**Immanuel Kant** (UK: /kænt/, US: /kɑːnt/; German: [ɪˈmaːnu̯eːl ˈkant, -nu̯ɛl -]; 22 April 1724 – 12 February 1804) was a German philosopher and one of the central Enlightenment thinkers. 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 that space and time are mere "forms of intuition" which structure all experience, and therefore that while "things-in-themselves" exist and contribute to experience, they are nonetheless distinct from the objects of experience. From this it follows that the objects of experience are mere "appearances", and that the nature of things as they are in themselves is consequently unknowable to us. In an attempt to counter the skepticism he found in the writings of philosopher David Hume, he wrote the *Critique of Pure Reason* (1781/1787), one of his most well-known works. In it, he developed his theory of experience to answer the question of whether synthetic *a priori* knowledge is possible, which would in turn make it possible to determine the limits of metaphysical inquiry. Kant drew a parallel to the Copernican revolution in his proposal that the objects of the senses must conform to our spatial and temporal forms of intuition, and that we can consequently have *a priori* cognition of the objects of the senses.

Kant believed that reason is also the source of morality, and that aesthetics arise from a faculty of disinterested judgment. Kant's views continue to have a major influence on contemporary philosophy, especially the fields of epistemology, ethics, political theory, and post-modern aesthetics. He attempted to explain the relationship between reason and human experience and to move beyond what he believed to be the failures of traditional philosophy and metaphysics. He wanted to put an end to what he saw as an era of futile and speculative theories of human experience, while resisting the skepticism of thinkers such as Hume. He regarded himself as showing the way past the impasse between rationalists and empiricists, and is widely held to have synthesized both traditions in his thought.

Kant was an exponent of the idea that perpetual peace could be secured through universal democracy and international cooperation, and that perhaps this could be the culminating stage of world history. The nature of Kant's religious views continues to be the subject of scholarly dispute, with viewpoints ranging from the impression that he shifted from an early defense of an ontological argument for the existence of God to a principled agnosticism, to more critical treatments epitomized by Schopenhauer, who criticized the imperative form of Kantian ethics as "theological morals" and the "Mosaic Decalogue in disguise", and Nietzsche, who claimed that Kant had "theologian blood" and was merely a sophisticated apologist for traditional Christian faith. Beyond his religious views, Kant has also been criticized for the racism presented in some of his lesser-known papers, such as "On the Use of Teleological Principles in Philosophy" and "On the Different Races of Man". Although he was a proponent of scientific racism for much of his career, Kant's views on race changed significantly in the last decade of his life, and he ultimately rejected racial hierarchies and European colonialism in *Perpetual Peace: A Philosophical Sketch* (1795).

Kant published other important works on ethics, religion, law, aesthetics, astronomy, and history during his lifetime. These include the *Universal Natural History* (1755), the *Critique of Practical Reason* (1788), the *Critique of Judgment* (1790), *Religion within the Bounds of Bare Reason* (1793), and the *Metaphysics of Morals* (1797).

## Contents

* 1Biography
	+ 1.1Young scholar
	+ 1.2Early work
	+ 1.3*Critique of Pure Reason*
	+ 1.4Later work
	+ 1.5Death and burial
* 2Philosophy
	+ 2.1Theory of perception
	+ 2.2Categories of the Faculty of Understanding
	+ 2.3Transcendental schema doctrine
	+ 2.4Moral philosophy
		- 2.4.1First formulation
		- 2.4.2Second formulation
		- 2.4.3Third formulation
		- 2.4.4*Religion within the Bounds of Bare Reason*
		- 2.4.5Idea of freedom
		- 2.4.6Categories of freedom
	+ 2.5Aesthetic philosophy
	+ 2.6Political philosophy
	+ 2.7Anthropology
		- 2.7.1Racism
* 3Influence
	+ 3.1Historical influence
	+ 3.2Influence on modern thinkers
* 4Bibliography
	+ 4.1List of major works
	+ 4.2Collected works in German
	+ 4.3External Link: *Elektronische Edition der Gesammelten Werke Immanuel Kants*. Volumes 1-23.
* 5See also
* 6Notes
* 7References
	+ 7.1Works cited
* 8Further reading
* 9External links

## Biography[edit]

Kant's mother, Anna Regina Reuter (1697–1737), was born in Königsberg (since 1946 the city of Kaliningrad, Kaliningrad Oblast, Russia) 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). Kant believed that his paternal grandfather Hans Kant was of Scottish origin. While scholars of Kant's life long accepted the claim, there is no evidence that Kant's paternal line was Scottish and it is more likely that the Kants got their name from the village of Kantwaggen (today part of Priekulė) and were of Curonian origin. Kant was the fourth of nine children (four of whom reached adulthood).

Kant was born on 22 April 1724 into a Prussian German family of Lutheran Protestant faith in Königsberg, East Prussia. Baptized Emanuel, he later changed the spelling of his name to Immanuel after learning Hebrew. He was brought up in a Pietist household that stressed religious devotion, humility, and a literal interpretation of the Bible.[*citation needed*] His education was strict, punitive and disciplinary, and focused on Latin and religious instruction over mathematics and science. Kant maintained Christian ideals for some time, but struggled to reconcile the faith with his belief in science. In his *Groundwork of the Metaphysic of Morals*, he reveals a belief in immortality as the necessary condition of humanity's approach to the highest morality possible. However, as Kant was skeptical about some of the arguments used prior to him in defence of theism and maintained that human understanding is limited and can never attain knowledge about God or the soul, various commentators have labelled him a philosophical agnostic.

Kant apparently lived a very strict and disciplined life; it was said that neighbors would set their clocks by his daily walks. He never married, but seemed to have a rewarding social life — he was a popular teacher and a modestly successful author even before starting on his major philosophical works. He had a circle of friends with whom he frequently met, among them Joseph Green, an English merchant in Königsberg.

Between 1750 and 1754 Kant worked as a tutor (*Hauslehrer*) in Judtschen (now Veselovka, Russia, approximately 20 km) and in Groß-Arnsdorf (now Jarnołtowo near Morąg (German: Mohrungen), Poland, approximately 145 km).

Many myths grew up about Kant's personal mannerisms; these are listed, explained, and refuted in Goldthwait's introduction to his translation of *Observations on the Feeling of the Beautiful and Sublime*.

### Young scholar[edit]

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.

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 1745–47).

### Early work[edit]

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 1757, Kant began lecturing on geography being one of the first people 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.
Kant's house in Königsberg
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 (though through usually false premises and fallacious reasoning, according to Bertrand Russell) 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. According to Thomas Huxley (1867), Kant also made contributions to geology in his *Universal Natural History*.[*citation needed*]

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 *Dreams of a Spirit-Seer* which dealt with the writings of Emanuel Swedenborg. The exact influence of Swedenborg on Kant, as well as the extent of Kant's belief in mysticism according to *Dreams of a Spirit-Seer*, remain controversial. 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.

The issue that vexed Kant was central to what 20th-century scholars called "the philosophy of mind". The flowering of the natural sciences had led to an understanding of how data reaches the brain. Sunlight falling on an object is reflected from its surface in a way that maps the surface features (color, texture, etc.). The reflected light reaches the human eye, passes through the cornea, is focused by the lens onto the retina where it forms an image similar to that formed by light passing through a pinhole into a camera obscura. The retinal cells send impulses through the optic nerve and then they form a mapping in the brain of the visual features of the object. The interior mapping is not the exterior object, and our belief that there is a meaningful relationship between the object and the mapping in the brain depends on a chain of reasoning that is not fully grounded. But the uncertainty aroused by these considerations, by optical illusions, misperceptions, delusions, etc., are not the end of the problems.

Kant saw that the mind could not function as an empty container that simply receives data from outside. Something must be giving order to the incoming data. Images of external objects must be kept in the same sequence in which they were received. This ordering occurs through the mind's intuition of time. The same considerations apply to the mind's function of constituting space for ordering mappings of visual and tactile signals arriving via the already described chains of physical causation.

It is often claimed that Kant was a late developer, that he only became an important philosopher in his mid-50s 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.

### *Critique of Pure Reason*[edit]

Main article: 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—i.e. reasoned knowledge—these two being related but having very different processes.
Portrait of philosopher David Hume
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* ('beforehand'), 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. It received few reviews, and these granted it no significance.[*citation needed*] Kant's 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. These well-received and readable tracts include one on the earthquake in Lisbon that was so popular that it was sold by the page. Prior to the change in course documented in the first Critique, his books had sold well. Kant was disappointed with the first Critique's reception. 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) (professor of mathematics) published *Erläuterungen über des Herrn Professor Kant Critik der reinen Vernunft* (Königsberg, 1784), which was a brief but very accurate commentary on Kant's *Critique of Pure Reason*.
Engraving of Immanuel Kant
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 Dispute. 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[edit]

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 Judgment* (the third *Critique*) applied the Kantian system to aesthetics and teleology. It was in this critique where Kant wrote one of his most popular statements: "it is absurd to hope that another Newton will arise in the future who will make comprehensible to us the production of a blade of grass according to natural laws".

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*.
Kant with friends, including Christian Jakob Kraus, Johann Georg Hamann, Theodor Gottlieb von Hippel and Karl Gottfried Hagen
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 18th-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 into increasingly radical forms of idealism. 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 *Auszug aus der Vernunftlehre*, 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[edit]

Kant's health, long poor, worsened and 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. Was Kant's forehead shaped this way in these images because he was a philosopher, or, to follow the implications of Lavater's system, was he a philosopher because of the intellectual acuity manifested by his forehead? Kant and Johann Kaspar Lavater were correspondents on theological matters, and Lavater refers to Kant in his work "Physiognomic Fragments, for the Education of Human Knowledge and Love of People" (Leipzig & Winterthur, 1775–1778).
Kant's tomb in Kaliningrad, Russia
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 conquered and annexed 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 stood in German times 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.

In late November 2018, his tomb and statue were vandalized with paint by unknown assailants, who also scattered leaflets glorifying Rus' and denouncing Kant as a "traitor". The incident is apparently connected with a recent vote to rename Khrabrovo Airport, where Kant was in the lead for a while, prompting Russian nationalist resentment.

## Philosophy[edit]

Main article: Kantianism

In Kant's essay "Answering the Question: What is Enlightenment?", he defined the Enlightenment as an age shaped by the Latin motto *Sapere aude* ("Dare to be wise"). Kant maintained that one ought to think autonomously, free of the dictates of external authority. His work reconciled many of the differences between the rationalist and empiricist traditions of the 18th century. He had a decisive impact on the Romantic and German Idealist philosophies of the 19th century. His work has also been a starting point for many 20th century philosophers.

Kant asserted that, because of the limitations of argumentation in the absence of irrefutable evidence, no one could really know whether there is a God and an afterlife or not. For the sake of morality and as a ground for reason, Kant asserted, people are justified in believing in God, even though they could never know God's presence empirically.
Immanuel Kant by Carle Vernet (1758–1836)
The sense of an enlightened approach and the critical method required that "If one cannot prove that a thing *is,* he may try to prove that it is *not.* If he fails to do either (as often occurs), he may still ask whether it is in his *interest* to *accept* one or the other of the alternatives hypothetically, from the theoretical or the practical point of view. Hence the question no longer is as to whether perpetual peace is a real thing or not a real thing, or as to whether we may not be deceiving ourselves when we adopt the former alternative, but we must *act* on the supposition of its being real." The presupposition of God, soul, and freedom was then a practical concern, for

Kant drew a parallel between the Copernican revolution and the epistemology of his new transcendental philosophy, involving two interconnected foundations of his "critical philosophy":

* the epistemology of transcendental idealism and
* the moral philosophy of the autonomy of practical reason.

These teachings placed the active, rational human subject at the center of the cognitive and moral worlds. Kant argued that the rational order of the world as known by science was not just the accidental accumulation of sense perceptions.

Conceptual unification and integration is carried out by the mind through concepts or the "categories of the understanding" operating on the perceptual manifold within space and time. The latter are not concepts, but are forms of sensibility that are *a priori* necessary conditions for any possible experience. Thus the objective order of nature and the causal necessity that operates within it depend on the mind's processes, the product of the rule-based activity that Kant called, "synthesis." There is much discussion among Kant scholars about the correct interpretation of this train of thought.

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 *transcendental 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.

The notion of the "thing in itself" was much discussed by philosophers after Kant. It was argued that because the "thing in itself" was unknowable, its existence must not be assumed. Rather than arbitrarily switching to an account that was ungrounded in anything supposed to be the "real," as did the German Idealists, another group arose to ask how our (presumably reliable) accounts of a coherent and rule-abiding universe were actually grounded. This new kind of philosophy became known as Phenomenology, and its founder was Edmund Husserl.

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. This necessitates practical self-reflection in which we universalize our reasons.

These ideas have largely framed or influenced all subsequent philosophical discussion and analysis. The specifics of Kant's account generated immediate and lasting controversy. Nevertheless, his theses – that the mind itself necessarily makes a constitutive contribution to its knowledge, that this contribution is transcendental rather than psychological, that philosophy involves self-critical activity, that morality is rooted in human freedom, and that to act autonomously is to act according to rational moral principles – have all had a lasting effect on subsequent philosophy.

### Theory of perception[edit]

Main article: Critique of Pure Reason

Kant defines his theory of perception in his influential 1781 work the *Critique of Pure Reason*, which has often been cited as the most significant volume of metaphysics and epistemology in modern philosophy. Kant maintains that understanding of the external world had its foundations not merely in experience, but in both experience and *a priori* concepts, thus offering a *non-empiricist critique of rationalist philosophy*, which is what has been referred to as his Copernican revolution.

Firstly, Kant distinguishes between analytic and synthetic propositions:

1. **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."
2. **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."

An analytic proposition is true by nature of the meaning of the words in the sentence — we require no further knowledge than a grasp of the language to understand this proposition. On the other hand, a synthetic statement is one that tells us something about the world. The truth or falsehood of synthetic statements derives from something outside their linguistic content. In this instance, weight is not a necessary predicate of the body; until we are told the heaviness of the body we do not know that it has weight. In this case, experience of the body is required before its heaviness becomes clear. Before Kant's first Critique, empiricists (cf. Hume) and rationalists (cf. Leibniz) assumed that all synthetic statements required experience to be known.

Kant contests this assumption by claiming that elementary mathematics, like arithmetic, is synthetic *a priori*, in that its statements provide new knowledge not derived from experience. This becomes part of his over-all argument for transcendental idealism. That is, he argues that the possibility of experience depends on certain necessary conditions — which he calls *a priori* forms — and that these conditions structure and hold true of the world of experience. His main claims in the "Transcendental Aesthetic" are that mathematic judgments are synthetic *a priori* and that space and time are not derived from experience but rather are its preconditions.

Once we have grasped the functions of basic arithmetic, we do not need empirical experience to know that 100 + 100 = 200, and so it appears that arithmetic is analytic. However, that it is analytic can be disproved by considering the calculation 5 + 7 = 12: there is nothing in the numbers 5 and 7 by which the number 12 can be inferred. Thus "5 + 7" and "the cube root of 1,728" or "12" are not analytic because their reference is the same but their sense is not — the statement "5 + 7 = 12" tells us something new about the world. It is self-evident, and undeniably *a priori*, but at the same time it is synthetic. Thus Kant argued that a proposition can be synthetic and *a priori*.

Kant asserts that experience is based on the perception of external objects and *a priori* knowledge. The external world, he writes, provides those things that we sense. But our mind processes this information and gives it order, allowing us to comprehend it. Our mind supplies the conditions of space and time to experience objects. According to the "transcendental unity of apperception", the concepts of the mind (Understanding) and perceptions or intuitions that garner information from phenomena (Sensibility) are synthesized by comprehension. Without concepts, perceptions are nondescript; without perceptions, concepts are meaningless. Thus the famous statement: "Thoughts without content are empty, intuitions [perceptions] without concepts are blind."

Kant also claims that an external environment is necessary for the establishment of the self. Although Kant would want to argue that there is no empirical way of observing the self, we can see the logical necessity of the self when we observe that we can have different perceptions of the external environment over time. By uniting these general representations into one global representation, we can see how a transcendental self emerges. "I am therefore conscious of the identical self in regard to the manifold of the representations that are given to me in an intuition because I call them all together **my** representations, which constitute **one**."

### Categories of the Faculty of Understanding[edit]

See also: Category (Kant)
Kant statue in the School of Philosophy and Human Sciences (FAFICH) in the Federal University of Minas Gerais (UFMG), Belo Horizonte, Brazil
Kant deemed it obvious that we have some objective knowledge of the world, such as, say, Newtonian physics. But this knowledge relies on synthetic, *a priori* laws of nature, like causality and substance. How is this possible? Kant's solution was that the subject must supply laws that make experience of objects possible, and that these laws are synthetic, *a priori* laws of nature that apply to all objects before we experience them. To deduce all these laws, Kant examined experience in general, dissecting in it what is supplied by the mind from what is supplied by the given intuitions. This is commonly called a transcendental deduction.

To begin with, Kant's distinction between the *a posteriori* being contingent and particular knowledge, and the *a priori* being universal and necessary knowledge, must be kept in mind. If we merely connect two intuitions together in a perceiving subject, the knowledge is always subjective because it is derived *a posteriori,* when what is desired is for the knowledge to be objective, that is, for the two intuitions to refer to the object and hold good of it for anyone at any time, not just the perceiving subject in its current condition. What else is equivalent to objective knowledge besides the *a priori* (universal and necessary knowledge)? Before knowledge can be objective, it must be incorporated under an *a priori* category of *understanding*.

For example, if a subject says, "The sun shines on the stone; the stone grows warm," all he perceives are phenomena. His judgment is contingent and holds no necessity. But if he says, "The sunshine causes the stone to warm," he subsumes the perception under the category of causality, which is not found in the perception, and necessarily synthesizes the concept sunshine with the concept heat, producing a necessarily universally true judgment.

To explain the categories in more detail, they are the preconditions of the construction of objects in the mind. Indeed, to even think of the sun and stone presupposes the category of subsistence, that is, substance. For the categories synthesize the random data of the sensory manifold into intelligible objects. This means that the categories are also the most abstract things one can say of any object whatsoever, and hence one can have an *a priori* cognition of the totality of all objects of experience if one can list all of them. To do so, Kant formulates another transcendental deduction.

Judgments are, for Kant, the preconditions of any thought. Man thinks via judgments, so all possible judgments must be listed and the perceptions connected within them put aside, so as to make it possible to examine the moments when *the understanding* is engaged in constructing judgments. For the categories are equivalent to these moments, in that they are concepts of intuitions in general, so far as they are determined by these moments universally and necessarily. Thus by listing all the moments, one can deduce from them all of the categories.

One may now ask: How many possible judgments are there? Kant believed that all the possible propositions within Aristotle's syllogistic logic are equivalent to all possible judgments, and that all the logical operators within the propositions are equivalent to the moments of the understanding within judgments. Thus he listed Aristotle's system in four groups of three: quantity (universal, particular, singular), quality (affirmative, negative, infinite), relation (categorical, hypothetical, disjunctive) and modality (problematic, assertoric, apodeictic). The parallelism with Kant's categories is obvious: quantity (unity, plurality, totality), quality (reality, negation, limitation), relation (substance, caus