Immanuel Kant was born in 1724 in Königsberg, Prussia (since 1946 the city of Kaliningrad, Kaliningrad Oblast, Russia). His mother, Anna Regina Reuter (1697–1737), was born in Nuremberg. His 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's paternal grandfather, Hans Kant, had emigrated from Scotland to East Prussia, and his father still spelled their family name "Cant". Kant was the fourth of nine children (four of them reached adulthood). Baptized 'Emanuel', he changed his name to 'Immanuel' after learning Hebrew.
Young Kant was a solid, albeit unspectacular, student. He was brought up in a Pietist household that stressed religious devotion, humility, and a literal interpretation of the Bible. His education was strict, punitive and disciplinary, and focused on Latin and religious instruction over mathematics and science. Despite his religious upbringing and maintaining a belief in God, Kant was skeptical of religion in later life; various commentators have labelled him agnostic.
Common myths about Kant's personal mannerisms are listed, explained, and refuted in Goldthwait's introduction to his translation of Observations on the Feeling of the Beautiful and Sublime. It is often held that Kant lived a very strict and predictable life, leading to an oft-repeated story 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.
A common myth is that Kant never traveled more than 10 miles (16 km) from Königsberg his whole life. In fact, between 1750 and 1754 he worked as a tutor (Hauslehrer) in Judtschen (now Veselovka, Russia, approximately 20 km) and in Groß-Arnsdorf (now near Elbląg, Poland, approximately 105 km).
Kant showed a great aptitude for study at an early age. He first attended the Collegium Fridericianum. 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, 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 developed in the Critique of Pure Reason is not traditional idealism and the Critique's second part even argues against traditional idealism.)
His father's stroke and subsequent death in 1746 interrupted his studies. Kant became a private tutor in the towns surrounding Königsberg, but continued his scholarly research. In 1747, he published his first philosophical work, Thoughts on the True Estimation of Living Forces.
Kant is best known for his work in the philosophy of ethics and metaphysics, but he made significant contributions to other disciplines. He made an important astronomical discovery about the nature of Earth's rotation, for which he won the Berlin Academy Prize in 1754.
According to Lord Kelvin:
"Kant pointed out in the middle of last century, what had not previously been discovered by mathematicians or physical astronomers, that the frictional resistance against tidal currents on the earth's surface must cause a diminution of the earth's rotational speed. This immense discovery in Natural Philosophy seems to have attracted little attention—indeed to have passed quite unnoticed—among mathematicians, and astronomers, and naturalists, until about 1840, when the doctrine of energy began to be taken to heart."—Lord Kelvin, physicist, 1897
According to Thomas Huxley:
"The sort of geological speculation to which I am now referring (geological aetiology, in short) was created as a science by that famous philosopher, Immanuel Kant, when, in 1775 , he wrote his General Natural History and Theory of the Celestial Bodies; or, an Attempt to Account for the Constitutional and Mechanical Origin of the Universe, upon Newtonian Principles."—Thomas H. Huxley, 1869
In the General History of Nature and Theory of the Heavens (Allgemeine Naturgeschichte und Theorie des Himmels) (1755), Kant laid out the Nebular hypothesis, in which he deduced that the Solar System formed from a large cloud of gas, a nebula. Thus he tried to explain the order of the solar system, which Isaac Newton had explained as imposed from the beginning by God. Kant also correctly deduced that the Milky Way was a large disk of stars, which he theorized also formed from a (much larger) spinning cloud of gas. He further suggested that other nebulae might also be similarly large and distant disks of stars. These postulations opened new horizons for astronomy: for the first time extending astronomy beyond the solar system to galactic and extragalactic 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. In 1764, Kant wrote Observations on the Feeling of the Beautiful and Sublime and then 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 1770, aged 45, Kant was finally appointed Professor of Logic and Metaphysics at the University of Königsberg. Kant wrote his inaugural dissertation in defense of this appointment. 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.
The silent decade
At age 46, Kant was an established scholar and an increasingly influential philosopher. 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 sensory knowledge with reasoned knowledge, these being related but very different processes. He also credited David Hume with awakening him from "dogmatic slumber" (circa 1771). Hume had stated that experience consists only of sequences of feelings, images or sounds. Ideas such as "cause", goodness, or objects were not evident in experience, so why do we believe in the reality of these? Kant felt that reason could remove this skepticism, and he set himself to solving these problems. He did not publish any work in philosophy for the next 11 years.
Although fond of company and conversation with others, Kant isolated himself. He resisted friends' attempts to bring him out of his isolation. In 1778, in response to one of these offers by a former pupil, Kant wrote:
"Any change makes me apprehensive, even if it offers the greatest promise of improving my condition, and I am persuaded by this natural instinct of mine that I must take heed if I wish that the threads which the Fates spin so thin and weak in my case to be spun to any length. My great thanks, to my well-wishers and friends, who think so kindly of me as to undertake my welfare, but at the same time a most humble request to protect me in my current condition from any disturbance."
When Kant emerged from his silence in 1781, the result was the Critique of Pure Reason. Although now uniformly recognized as one of the greatest works in the history of philosophy, this Critique was largely ignored 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. 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 which 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 sold well, and by the time he published Observations on the Feeling of the Beautiful and Sublime in 1764 he had become a notable popular author. 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 ūber des Herrn Professor Kant Critik der reinen Vernunft (Kōnigsberg, 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 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.
Kant published a second edition of the Critique of Pure Reason (Kritik der reinen Vernunft) 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.
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 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 (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 Freidrich 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."
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 wrote a book discussing his theory of virtue in terms of independence which he believed was "a viable modern alternative to more familiar Greek views about virtue". This book is often criticized for its hostile tone and for not articulating his thoughts about autocracy comprehensibly. In the self-governance model of Aristotelian virtue, the non-rational part of the soul can be made to listen to reason through training. Although Kantian self-governance appears to involve "a rational crackdown on appetites and emotions" with lack of harmony between reason and emotion, Kantian virtue denies requiring "self-conquest, self-suppression, or self-silencing". They dispute that "the self-mastery constitutive of virtue is ultimately mastery over our tendency of will to give priority to appetite or emotion unregulated by duty, it does not require extirpating, suppressing, or silencing sensibility in general".