German philosopher, professor of logic and metaphysics, whose masterpiece, The Critique of Pure Reason, appeared in 1781 and then in a substantially revised edition in 1787. The work was an answer to Descartes's skepticism about knowledge. Kant's aim was to make philosophy, for the first time, truly scientific, but his jargon made his central writings nearly impossible for the uninitiated to understand. Even professional philosophers have had problems with Kant. A.J. Ayer (1910-1989), the writer of Language, Truth and Logic, tells that he read The Critique on a ship bound for the Gold Coast. After a sunstroke, he fully grasped Kant's work in a state of epiphany, but once he had recovered he had lost the insight.

"Two things fill the mind with ever-increasing wonder and awe, the more often and the more intensely the mind of thought is drawn to them: the starry heavens above me and the moral law within me." (from Citique of Practical Reason, 1799)

Immanuel Kant was born in Königsberg (Kaliningrad), which then was the eastern part of Prussia. His father, Johann Georg Kant, was a poor but respected saddler, whose strict pietistic Protestantism made a lasting impression upon his son. Johann's wife, Anna Regina (née Reuter), was the daughter of another harness maker. Immanuel was the fourth child, but two of his siblings had already died. Of the five siblings born after him, only three survived early childhood.

Kant attended the Collegium Fridericianum, and at the age of 16 he entered the University of Köningsberg, where he studied philosophy, mathematics, and physics, and attended lectures in theology. When his father died in 1746, Kant's financial situation became difficult. His mother had died nine years earlier. To earn his living, he served as a private tutor from 1747 to 1754 in various provincial households. Though penniless he found much time for scientific research. In General History of Nature and Theory of the Heavens (1755) he argued that the system of heavenly bodies could have developed from an unformed nebula. His doctor's degree Kant received for the work On Fire, and was appointed a lecturer at the university.

Kant taught logic, metaphysics, moral philosophy, natural theology, anthropology, as well as mathematics, physics, and physical geography. His income during the first years was very small, and he wore the same coat until it was worn out. When his friends refused to buy him a new one, he refused. Later in life he was known as a person of elegance. He was 1.57 meters tall (5 feet 2 inches), slender, with eyes of  light sky blue. One contemporary said: "It is impossible to describe the bewitched effect of his look on my feeling when I sat across him and when he suddenly raised his lowered eyes to look at me. I always felt as if I looked through this blue ether-like fire into the most holy of Minerva."

In 1756 Kant wrote on the earthquake in Lisbon, which his great French contemporary Voltaire dealt in the satirical story Candide (1759). Kant himself almost never laughed, and like Buster Keaton, he told funny anecdotes with a stone face. After he had unsuccessfully applied in 1758 for professorship, he wrote an essay on optimism. One of his students during the early sixties was Johann Gottfried Herder (1744-1893), who became one of the most important writers of the Sturm and Drang movement. Kant reviewed Herder's Ideen zur Philosophie der Geschichte der Menschheit (Ideas Toward a Philosophy of the History of Man) very critically. In 1766 he worked as an assistant-librarian in the royal palace. He declined the offers of professorship at the universities of Erlangen and Jena, and eventually in 1770 Kant was appointed professor of logic and metaphysics at Köningsberg. His inaugural dissertation was On the Forms and Principles of the Sensible and Intelligible World.

Before retiring, Kant served as the  dean of the faculties six times and rector of the university twice. During this period he published Critique of Pure Reason, Prolegomena to Any Future Metaphysics (1783), Critique of Practical Reason (1788), and Critique of Judgment (1790). Kant never left his home town to see the world beyond his limited horizon. Outside the walls of the university Rousseau published Confessions (1781), Goethe wrote Faust, and the French Revolution abolished absolute monarchy. Kant believed in his own rational thinking, and did not consider traveling necessary to solve the problems of philosophy. However, he was not withdrawn until late in life. He enjoyed conversation and was very interested in the accounts of travellers. His lectures were freely delivered, spiced with humor. Kant's friends included the famous Jewish philosopher Moses Mendelssohn, the writer Theodor Gottlieb Hippel, the book dealer and publisher Johann Jakob Kanter, Countess Caroline Charlotte Amalie Keyserlingk, the moral philosopher Jacob Christian Kraus, and the mathematician and philosopher Johann Heinrich Lambert. 

Kant's daily luncheons with his friends frequently ran on through the afternoon until four or five o'clock. His menus were simple: three courses, followed by cheese.Kant adored especially English cheese. All courses were accompanied with mustard. He drank red wine, usually Medoc, and white wine, as a way to of relieving the astringent after-effects of the red wine. After dinner he drank a glass of dessert wine, which was warmed and scented with orange peel.

According to an anecdote, Kant's life habits were so regular, that people used to set their clocks by him as the philosopher passed their houses on his daily walk – the only time when the schedule changed was when Kant read Jean-Jacques Rousseau's Emile, and forgot the walk. Martin Lampe, Kant's servant, was a retired soldier, who drank heavily. His last lecture Kant held in 1796. During the last years of his life, his physical and mental powers deteriorated noticeably. He developed delusions about electricity and began to believe that it causes peculiar configurations of clouds and a widespread disease amongst cats. In 1802 he dismissed Lampe, for treating him in a way which he was ashamed to repeat. In his diary he wrote: "The name of Lampe must now be remembered no more."

Kant died on February 12, 1804, less than two months before his eightieth birthday. For the next two weeks, people lined up to see his dried out corpse, which looked "like a skeleton that one might exhibit." Kant never married. After his death an anonymous writer, most probably Johann Daniel Metzger, a professor of medicine at the university of Königsberg, published a book which slandered Kant's character: he was an egoist and a miser, did not tolerate criticism, disliked religious people, mistreated his servans, and his sister was not allowed to eat at his table. Moreover, he defended the principles of the French Revolution.  

Kant's output was large but he produced his most important works, the three Critiques, late in life. His attempts to establish an objective basis for aesthetic judgments have influenced later art criticism. In Critique of Judgment he argued that aesthetic judgments do not depend on any property – such as beauty – of the object. Kant's famous contribution to moral philosophy is the principle "act only on that maxim through which you can at the same time will that it should to become a universal law."

In The Critique of Pure Reason Kant wanted to prove, that although our knowledge is derived from experience, it is possible to have knowledge of objects in advance of experience. The key question is how are synthetic a priori judgments possible? An a priori knowledge is knowledge which is independent of all experience. A priori proposition is one that can be known to be true, or false, without reference to experience, except so far as experience is necessary for understanding its terms. 

An analytic truth can be deduced from the definition of its terms, and a synthetic truth cannot be so deduced. Such propositions as 'All bodies are extended in space' or 'All husbands are male' are analytical, because the ideas of extension and maleness are already contained in those of 'body' and 'male.' Analytical propositions are not dependent on experience for their validations; if true they are necessary true a priori. On the other hand, 'Some bodies are heavy' is synthetic, since the idea of heaviness is not necessarily contained in the subject idea. Synthetic propositions are always contingent; any such proposition is capable of being true or false. Its truth could be known only a posteriori, after it had received validation from experience. An a posteriori knowledge is derived from experience. A posteriori preposition can be known to be true, or false, only by reference to how, as a matter of contingent fact, things have been, are, or will be. 'Every change has a cause,' expresses a judgment which is strictly necessary and universal. 'All bodies are heavy' is simply a generalization to which no exception have been observed.

Accoding to Hume, all significant propositions must be either (i) synthetic and a posteriori or (ii) analytic and a priori. But Kant stated that there is a third category, namely synthetic a priori. Kant firmly believed in an independent reality outside the world of all possible experience, calling this the world of the noumenal, the world of things as they are in themselves, and of reality as it is in itself. A Kantian synonym for noumenon is Ding an Sich. The world of phenomena is the world of things as they appears to us – the directly known world of actual experience.

Noumena are delimeted since they cannot be known. Thus he developed three cognitive faculties, imagination, understanding, and reason, and through their relationships he examined "the science of relation of all knowledge to the essential ends of human reason." Kant  suggested, that the way in which we perceive, identify, and reflect upon objects might have itself a form or structure which in some ways moulds or contributes to our experience.

According to Kant, all that our senses and understanding contribute to knowledge is preconditioned by the 'forms of our sensibility' (space and time) and by the 'categories of our understanding' that are not learned from experience, but enable us to make sense of our experience. Among the twelve categories are space, time, quantity, quality, relation, modality, and their subforms. They are essential if any creature is going to be able to make judgments about his experience. Together they form a sort of minimum conceptual apparatus for making sense of the world. What we experience can come to us wholly and solely in terms of the a priori framework. We don't synthesize reality, make it up, it exists independently of us. Because reality exists independently of all possible experience it remains permanently hidden.

Thus Kant's conclusion was, that cognition is restricted to the realm of phenomena, meaning appearances. We can know nothing which cannot be given through our senses. Within these limitations we may have valid empirical knowledge, and a cognition a priori of the universal conditions which make nature itself and a science of nature possible. Kant believed that Newton had proved beyond any possibility of doubt, that what happens within this world is governed entirely by scientific laws. But without experience there can be no empirical world.

"What we have meant to say is that all our intuition is nothing but the representation of appearance; that the things which we intuit are not in themselves what we intuit them as being, nor their relations so constituted in themselves as they appear to us, and that if the subject, or even only the subjective constitution of the senses in general, be removed, the whole constitution and all the relations of objects in space and time, nay space and time themselves, would vanish. As appearances, they cannot exists in themselves, but only in us. What objects may be in themselves, and apart from all this receptivity of our sensibility, remains completely unknown to us. We know nothing but our mode of perceiving them – a mode which is peculiar to us, and not necessarily shared in by every being, though, certainly, by every human being. With this alone have we any concern." (from Critique of Pure Reason)

Especially Kant's philosophy of religion arose strong reaction, but the younger generation saw Kant as their intellectual leader. After receiving a letter in 1794, signed by the King, in which he was reproached for having "misused" his philosophy for the distortion of basic teachings of Holy Scripture and of Christianity, he did not discuss religious matters in public again.

Jena soon became the center of Kantian idealism, with such representatives as Johann Christoph Friedrich von Schiller, Johann Gottlieb Fichte, Friedrich Wilhelm Joseph von Schelling, and Georg Wilhelm Friedrich Hegel. In The World as Will and Representation Schopenhauer wrote: "Kant's teaching produces a fundamental change in every mind that has grasped it. This change is so great that it may be regarded as an intellectual rebirth. It alone is capable of really moving the inborn realism which arises from the original disposition of the intellect... In consequence of this, the mind undergoes a fundamental undeceiving, and thereafter looks at things in another light." From Schopenhauer Kant's influence continued to Nietzsche and through him to modern existentialism; another line of succession went to Wittgenstein and through him to modern analytic philosophy. Third line goes to science-based rationalism and Popper, who once remarked: "It was through Schopenhauer that I understood Kant."

For further reading: The Categorical Imperative by H.J. Paton (1947); Kantian Ethics by A.E. Teale (1951); Kant by Stephan Körner (1955); Kant's Theory of Knowlwdge by G. Bird (1962); The Bounds of Sense by P.F. Strawson (1966); Kant's Dialectic by J. Bennett (1974); Kant by R. Walker (1979); Kant's Theory of Mind by K. Ameriks (1982); Kant's Transcendental Idealaism by H. Allison (1983); The Coherence of Kant's Doctrine of Freedom by Bernard Carnois (1987); A Commentary on Kant's Critique of Pure Reason by Norman Kemp Smith (1991); The Cambridge Companion to Kant, ed. by Paul Guyer (1992); The Genesis of Kant's Citique of Judgment by John H. Zammito (1992); Essays on Kant's Political Philosophy by Howard Lloyd Williams (1992); Cognition and Eros by Robin May Schott (1993); The Embodiment of Reason by Susan Meld Shell (1996); A Commentary of Kant's Critique of Practical Reason by Lewis White Beck (1996); Feminist Interpretations of Immanuel Kant, ed. by Robin May Schott (1997); Agent-Centered Morality: An Aristotelian Alternative to Kantian Internalism by George W. Harris (1999); The Categorical Imperative by Herbert J. Paton (1999); Kant: A Very Short Introduction by Roger Scruton (2001); Kant: A Biography by Manfred Kuehn (2002); Kant's Critique of the Power of Judgment: Critical Essays, edited by Paul Guyer (2003); An Introduction to Kant's Aesthetics: Core Concepts and Problems by Christian Helmut Wenzel (2005)  See: Arthur Schopenhauer, Emanuel Swedenborg, Dashiell Hammett. See also: eLogic Gallery: Ancient Greece to the Enlightment by David Marans (an open-access pdf ebook) & Pantheon of Logic: Insights, Images, Bios, Links From Ancient Greece to the Twenty-First Century (full text eBook) by David Marans  

Selected works:

• Gedanken von der wahren Schätzung der lebendigen Kräfte und Beurtheilung der Beweise, deren sich Herr von Leibniz und andere Mechaniker in dieser Streitsache bedient haben, nebst einigen vorhergehenden Betrachtungen, welche die Kraft der Körper überhaupt betreffen, 1747
• Die Allgemeine Naturgeschichte und Theorie des Himmels, 1755
  - General History of Nature and Theory of the Heavens (translated by William Hastie, 1969) / Universal Natural History and Theory of the Heavens (translated by Stanley L. Jaki, 1981)
• Principiorum primorum cognitionis metaphysicae nova dilucidatio, 1755
  - 'A New Exposition of the First Principles of Metaphysical Knowledge' (translated by John A. Reuscher, in Latin Writings, edited by Lewis White Beck, 1986)
• Gedanken bei dem frühzeitigen Ableben des Herrn Johann Friedrich von Funk, 1760
• Die falsche Spitzfindigkeit der vier syllogistischen Figuren erwiesen, 1762
  - 'On the Mistaken Subtlety of the Four Syllogistic Figures' (translated byThomas K. Abbott, in Kant's Introduction to Logic, 1885)
• Der einzig mögliche Beweisgrund zu einer Demonstration des Daseyns Gottes, 1763
  - The Only Possible Ground for a Demonstration of the Existence of God (translated by G.B. Kerferd and D.W. Walford, 1968)
• Versuch den Begriff der negativen Größen in die Weltweisheit einzuführen, 1763
• Beobachtungen über das Gefühl des Schönen und Erhabenen, 1764
  - Observations on the Feeling of the Sublime and The Beautiful (translated by John T. Godthwait, 1960)
• Untersuchung über die Deutlichkeit der Grundsätze der natürlichen Theologie und der Moral, 1764
  - An Inquiry into the Distinctness of the Principles of Natural Theology and Morals (tr. 1949)
• Träume eines Geistersehers, erläutert durch Träume der Metaphysik, 1766
  - Dreams of a Spirit-Seer, Elucidated Through Dreams of Metaphysics (translated by Emanuel P. Goerwitz, 1900) / Dreams of a Spirit-See Elucidated by Dreams of Metaphysics (translated by David Walford, in Theoretical Philosophy, 1755-1770, 1992)
• De mundi sensibilis atque intelligibilis forma et pricipiis, 1770
  - 'On the Form and Principles of the Sensible and Intelligible World' (translated by John Handyside, in Latin Writings, ed. Lewis White Beck, 1986)
• Kritik der reinen Vernunft, 1781 (2nd ed., 1787)
  - Critique of Pure Reason (translated by J.M.D. Meiklejohn, 1855; Norman Kemp Smith, 1929)
• Prolegomena zu einer jeden künftigen Metaphysik die als Wissenschaft wird auftreten können, 1783
  - Prolegomena to Every Future Metaphysics (translated by John Richardson, 1819) / Prolegomena to Any Future Metaphysics (translated by Lewis White Beck, 1950) / Prolegomena to Any Future Metaphysics That Will Be Able to Present Itself as a Science (translated by P.G. Lucas, 1953)
  - Prolegomena, eli, Johdatus mihin tahansa metafysiikkaan, joka vastaisuudessa voi käydä tieteestä (suom. Vesa Oittinen, 1997)
• Die Idee zu einer allgemeinen Geschichte in weltbürgerlicher Absicht, 1784
  - Idea for a Universal History from a Cosmopolitan Point of View (translated by Lewis White Beck, in On History, 1963) / Idea for a Universal History with Cosmopilitan Intent (translated by Carl J. Friedrich, in The Philosophy of Kant, 1949)
• Die Grundlegung zur Metaphysik der Sitten, 1785
  - Fundamental Principles of the Metaphysics of Morals (translated by Thomas Abbott Kingsmill, 1909) /  Groundwork of the Metaphysics of Morals (translated by H.J. Patton, 1948) 
• Metaphysischen Anfangsgründe der Naturwissenschaft, 1786
  - Metaphysical Foundations of Natural Sciences (translated by James Ellington, 1970)
• Kritik der praktischen Vernunft, 1788
  - Critique of Practical Reason (translated by Lewis White Beck, in Critique of Practical Reason and Other Writings in Moral Philosophy, 1949)
  - Siveysopilliset pääteokset (suom. J. E. Salomaa, 1931)
• Kritik der Urteilskraft, 1790
  - Critique of Judgment (translated by John Henry Barnard, 1892) / Critique of Aesthetic Judgement (translated by James C. Meredith, 1911) / Critique of Judgement (translated by Werner S. Pluhar, 1987)
• Vom radicalen Bosen in der Menschennatur, 1792
  - On the Radical Evil in Human Nature (translated by Thomas Kingsmill Abbott, in Kant's Theory Of Ethics: Or Practical Philosophy, 1873)
  - Radikaali paha (suom. Markku Lehtinen, teoksessa Immanuel Kant: Radikaali paha. Paha eurooppalaisessa perinteessä, toim. Ari Hirvonen ja Toomas Kotkas, 2004)
• Religion innerhalb der Grenzen der blossen Vernunft, 1793
  - Religion Within the Limits of Reason Alone (translated by Theodore M. Greene and Hoyt H. Hudson, 1934)
• Zum ewigen Frieden. Ein philosophischer Entwurf, 1795
  - Perpetual Peace (translated by Lewis White Beck, 1957) / To Eternal Peace (translated by Carl J. Friedrich, in Basic Writings of Kant, ed. Allen W. Wood, 2001)
  - Ikuiseen rauhaan (suom. Jaakko Tuomikoski, 1922)
• Die Metaphysik der Sitten, 1797 (2 vols.)
  - The Metaphysical Elements of Justice (translated by J. Ladd, 1965) / The Doctrine of Virtue (vol. 2, translated by M.J. Gregor, 1964) / The Metaphysical Principles of Virtue (translated by J. Ellington, 1964)
  - Siveysopilliset pääteokset (suom. J. E. Salomaa, 1931)
• Anthropologie in pragmatischer Hinsicht, 1798
  - Anthropology from a Pragmatic Point of View (translated by J.M. Gregor, 1974)
• Der Streit der Fakultäten, 1798
  - The Conflict of the Faculties (translated by Mary J. Gregor, 1992)
  - Tiedekuntien riitely (suom. Heikki Kirjavainen, 1998)
• Essays and Treatises on Moral, Political, and Various Philosophical Subjects, 1798 (2 vols., translated by John Richardson)
• Logik: Ein Handbuch Zu Vorlesungen, 1800 (ed. G.B. Jäsche)
  - Kant's Logic (translated by R.S. Hartman and W. Schwartz, 1974)
• Über die Fortschritte der Metaphysik Seit Leibniz und Wolff, 1804
  - What Real Progress Has Metaphysics Made in Germany Since the Time of Leibniz and Wolff? (translated by Peter Heath, in Theoretical Philosophy after 1781, edited by Henry Allison and Peter Heath, 2002)  
• Gesammelten Schriften, 1902-55 (23 vols.)
• The Philosophy of Kant, 1949 (edited by Carl J. Friedrich)
• Philosophical Correspondence, 1759-99, 1967 (edited and translated by Arnulf Zweig)
• On History, 1963 (edited by Lewis White Beck)
• Werke in zwölf Bänden, 1968 (edited by W. Weischedel)
• Kant: Political Writings, 1970 (edited by H.S. Reiss, translated by H.B. Nisbet)
• Kleinere Schriften zur Geschichtsphilosophie, Ethik und Politik, 1973 (edited by K. Vorländer)
• Was Ist aufklärung? Aufsätze Zur Geschichte Und Philosophie, 1985 (edited by Jürgen Zehbe)
• Latin Writings, 1986 (edited by Lewis White Beck)
• Lectures on Logic, 1992 (translated and edited by J. Michael Young) 
• Raising the Tone in Philosophy: Late Essays by Immanuel Kant, Transformative Critique by Jacques Derrida, 1993 (translated by Peter Fenves)
• Practical Philosophy, 1996 (edited by Mary J. Gregor)
• Basic Writings of Kant, 2001 (edited by Allen W. Wood)
• Natural Science, 2012 (edited by Eric Watkins)