Kant is most famous for his view—called transcendental idealism
—that we bring innate
forms and concepts to the raw experience of the world, which otherwise would be completely unknowable. Kant's philosophy of nature and human nature is one of the most important historical sources of the modern conceptual relativism
that dominated the intellectual life of the 20th century
—though it is likely that Kant would reject relativism
in most of its more radical modern forms. Kant is also well-known and very influential for his moral philosophy. Kant also proposed the first modern theory of solar system
formation, known as the Kant-Laplace hypothesis
Kant was born lived and died in Königsberg (now Kaliningrad
). He spent much of his youth as a solid but not spectacular student, living more off playing pool than his writings. He was of the rather curious conviction that a person did not have a firm direction in life until their thirty-ninth year; when his came and passed and he was just a minor metaphysician in a Prussian University a brief mid-life crisis ensued; perhaps it can be credited with some of his later direction.
Kant was a respected and competent university professor for most of his life, although nothing he did until his late fifties would have gained him much if any historical repute. He lived a very regulated life: the walk he took at three-thirty every afternoon was so punctual that local housewives would set their clocks by him. He never left Prussia, and rarely stepped outside his own home town. Despite the reputation he has earned though, he was considered a very sociable person: he would regularly have guests over for dinner, insisting that sociable company was good for his constitution.
, when he was forty-six, Kant read the work of the Scottish philosopher David Hume
. Hume was fiercely empirical, scorned all metaphysics, and systematically debunked great quantities of it. His most famous thesis is that nothing in our experience can justify our assuming that there are "causal powers" inhering in things—that, for example, when one billiard ball strikes another the second one in any sense "must" move. Of course, things always have happened this way, and we tend through "custom and habit" to assume they will; but we have no rational grounds for doing so. Kant was profoundly bothered. He simultaneously found Hume's argument irrefutable and his conclusions unacceptable. For ten years he published nothing, and then in 1781
released the massive Critique of Pure Reason
, arguably the most significant single book in modern philosophy. In this he developed his notion of a transcendental argument to show that, in short, although we cannot know necessary truths about theworld "as it is in itself", we are nonetheless constrained to perceiving and thinking about the world in certain ways: we can know with certainty a great number of things about "the world as it appears to us": for example, that every event will be causally connected with others, that appearances in space and time will obey the laws of geometry and arithmetic, and so forth.
Over the next twenty-odd years until his death in 1804
Kant's output was unceasing. His edifice of Critical Philosophy was completed with theCritique of Practical Reason
, which dealt with morality (action) in the same way that the first Critique dealt with knowledge; and theCritique of Judgment
, which dealt with the various uses of our mental powers that neither confer factual knowledge nor determine us to action: aesthetic judgment (of the beautiful and sublime) and teleological judgment (construing things as having "purposes"). As Kant understood them, aesthetic and teleological judgment connected our moral and empirical judgments to one another, unifying his system.
Two shorter works, theProlegomena to any Future Metaphysics
and theGroundwork to the Metaphysics of Morals
treated the same matter as the first and second critiques respectively, in a more cursory form—assuming the answer and working backward, so to speak. They serve as excellent introductions to the critical system. The epistemological material of the first Critique was put into application in theMetaphysical Foundations of Natural Science
; the ethical dictums of the second were put into practice inMetaphysics of Morals
Aside from this Kant wrote a number of semi-popular essays on history, politics, and the application of philosophy to life. When he died he was working on a projected "fourth critique", having come to the conviction that his system was incomplete; this incomplete manuscript has been published asOpus Postumum
. Kant died in 1804
.Kant's philosophy in general
Though he adopted the idea of a critical philosophy
, the primary purpose of which was to "critique" or come to grips with the limitations of our mental capacities, Kant was one of the greatest of system builders, pursuing the idea of the critique through studies of metaphysics, ethics, and aesthetics.
One famous citation, "the starry heavens above me and the moral law within me", sums up his efforts: he wanted to explain in one systematic theory, those two areas or realms. Isaac Newton
had developed a theory of physics
that Kant wanted to build his philosophy upon. This theory involved the assumption of natural forces that humans cannot sense, but are used to explain movement of physical bodies.
His interest in science also led him to propose in 1755
that the solar system was created out of a gas cloud in which objects condensed due to gravity. This hypothesis is widely regarded as the first modern theory of solar system formation and is the ancestor to current theories of stellar formation.