Immanuel Kant was born in 1724 and died in 1804. He was the son of a poor saddle-maker, but because of his evident intelligence he was sent to university. After receiving a doctoral degree from the Faculty of Philosophy at the University of Konigsberg, he became first a private tutor for families in the area, and then a lecturer at the University of Konigsberg, at which he was to spend the rest of his life teaching. He lectured on a variety of topics including cosmology and anthropology, as well as philosophy.
Kant's major works of philosophy were all written fairly late in his life. The first of these was the Critique of Pure Reason, published in 1781, when Kant was fifty-seven. The Critique of Pure Reason is also known as Kant's first Critique, since it was followed in 1788 by a second Critique, the Critique of Practical Reason and in 1790 by a third Critique, the Critique of Judgment. Each of these books has had a tremendous impact on philosophy concerning its subject manner, which is metaphysics and epistemology for the first Critique, ethics for the second, and aesthetics for the third.
Kant lived an exceptionally quiet, uneventful, regular life, never marrying or traveling far from Konigsberg. His sedentary, routine life has often been the source of derision from his critics. Allegedly, the housewives of Konigsberg set their clocks every day of his professional life by his daily walk-except for one day when, in his engrossment with Jean Jacque Rousseau's novel Emile, he forgot the walk. On the other hand, Kant's heavy academic workload, moderate income, and weak health may go some ways towards explaining his uneventful life, and perhaps it is simply true that for him his intellectual adventures were adventures enough. We do know that he was quite sociable and also that he took great interest in the latest sciences, which should go some ways toward dispelling the image of Kant as bloodless and interested only in his own abstractions.
It has been suggested that Kant was affected by his upbringing as a Pietist, a Lutheran revivalist sect that emphasized moral self-examination over dogma and ritual. One possible sign of this upbringing lies in his understanding of moral worth, which depends on the inner reason the person has for an action rather than on the effects or appearance of the action. Another sign of his upbringing lies in his understanding of religion; although Kant rejects most of the traditional Christian system with its anthropomorphic God and its accompanying rituals, he still regards himself as having saved all worthwhile features of religion.
The religion Kant justifies in the Critique of Practical Reason provides a God who guarantees that moral dutifulness will lead to good, but nothing else. He includes nothing about Christ, nothing about God's will, nothing about the efficacy of prayer. None of this is ruled out, but neither is it promised.
Kant can be regarded as both a participant in the eighteenth century Enlightenment and as a critic of it. He certainly agreed with the French Encyclopedists in celebrating rationality, and in regarding the achievement of his age as that of gradually bringing reason to bear against the forces of superstition, in both the area of science and the realm of religion. (For more about his attitude, see his 1784 essay "An Answer to the Question: What is Enlightenment.") At the same time, however, Kant's philosophy attacks several groups that may be seen as carrying reason too far: metaphysicists who presume to understand God and immortality, scientists who presume their results to describe the intrinsic nature of reality, skeptics who presume to show belief in God, freedom, and immortality to be irrational.
Besides his belief in the importance of rationality, Kant also shared the Enlightenment view that all humans are capable of reason and hence that all are endowed with moral worth. For this reason, he was an enthusiastic supporter of the French Revolution; although saddened by its excesses, Kant regarded the revolution as moving toward a form of government that would recognize the equal worth of all people from a form of government that did not. Although the Critique of Practical Reason is not an explicitly political book, and although Kant was forced even in his political books to refrain from overt support for the revolution for fear of censorship, the following Critique of Practical Reason can be regarded as expressing the view of morality that underlay his revolutionary sentiments.
Kant's other intellectual influences included the Newtonian mechanics of the day, the rationalistic Leibniz-inspired metaphysics of Christian Wolff, a contemporary, and the skeptical empiricism of David Hume, a philosopher of the Scottish Enlightenment. Kant's metaphysics can also be seen as attempting to reconcile the rationalist and empiricist movements.
It is difficult to overestimate Kant's influence in philosophy. Even those who reject his explicit theories often use his terms, whether by wondering how it could be possible for something to be "synthetic" (not a matter of meaning) and yet "a priori" (knowable independent of experience), or by asking what is the source of an ethical "imperative." Kant has sometimes been credited for almost single-handedly creating the German philosophical tradition, and it certainly is hard to imagine what Hegel's or Marx's wrings would have looked like without the influence of Kant.
Many current day writers on philosophical ethics have been influenced by Kant. Some accept the categorical imperative as a valid test of moral rightness, but more commonly one will see Kant's linking of morality and autonomy, or his analysis of moral worth as an inner acceptance of the motive of duty, or his insistence that the good is what the moral aims at as opposed to morality being defined by its aim at the good.
The impact of Kant's writing style has arguably also been extensive, on which topic the twentieth century philosophy Walter Kaufmann tartly reports, "Few philosophers since Kant have approximated his genius, but many of his shortcomings are widely shared even today, and to some extant at least this is due to his phenomenal influence." Kant's insights are often masked by his convoluted sentences and unclear technical terms. Fortunately, the second Critique is significantly more accessible than the first, but still the second Critique elicits many conflicting interpretations.
The Critique of Practical Reason can be regarded as the sequel to the Critique of Pure Reason, picking up where that earlier book left off. In the first Critique, Kant divides our judgments in two ways—the a priori (knowable before experience) versus the a posteriori (knowable through experience) and the analytic (true by virtue of meaning) versus the synthetic (true by virtue of the facts). He ultimately concludes, first, that a posteriori judgments are about how things look to us, not about how things intrinsically are, since they are filtered through our experiences, and, second, all synthetic judgments are a posteriori, since we have no access to the world other than through experience.
This second conclusion rules out the possibility of metaphysically proving the existence of God, freedom, and immortality. It does leave open, though, the right to have faith that such things exist in the way the world is in itself, the noumenal realm, since we can never know what is true in that realm. The second Critique will take this further, arguing that the correct understanding of morality requires us to believe in God, freedom, and immortality. As well as continuing from the Critique of Pure Reason, the Critique of Practical Reason lays the grounds for the Metaphysics of Morals, written nine years later in 1797, and which applies the general moral principles of the second Critique to a variety of cases.
The second Critique in some senses can be seen as the opposite of the first Critique. While the main theme of the first Critique is how little we can know about its topic, metaphysics, the second Critique is about how we can know about its topic, morality. Not only that, but some of the first Critique is arguably taken back. We are directly aware of the application of the moral law to us, and through this, we are aware of our freedom, which, it turns out, is awareness of causation from the noumenal world. More than that, not only can we believe in God and immortality, as the first Critique agreed, but it turns out that reason commands belief in them.
In a different sense, though, the second Critique furthers the work of the first. Kant describes himself in the Critique of Pure Reason as having created a revolution to counter Copernicus'. Copernicus humbles man by removing him form the center of the physical universe, but Kant elevates him by presenting the whole phenomenal world of the senses as being created by us and by our senses. In the conclusion of the second Critique, Kant picks up this metaphor again, explaining how he has now shown how the human being lies at the center of the moral universe, and through that universe man connects with the noumenal world.