Immanuel Kant: The Philosopher Who Defined Modern Thought

In the Critique of Pure Reason, in the preface to the second edition of 1787, Kant reports that the work of the first edition, in 1781, was interrupted by a reading of David Hume, which “first interrupted my dogmatic slumber and gave my investigations in the field of speculative philosophy a quite new direction.” The story has been the basis of a thousand textbook accounts of the relation between Hume and Kant — Hume the destroyer, Kant the rebuilder — and it is, in its bare outline, true. It is also, like most philosophical autobiographies, more useful for the picture Kant wanted to give of his own development than for the development itself.

The actual relationship is more interesting. Kant had been working on the problem of the Critique for at least ten years before he read Hume in 1770, and the doctrine of the first edition — the transcendental idealism of the A edition, with its sharp distinction between the world of appearance and the thing in itself, and its carefully limited account of the human knowledge of the noumenal world — is, in fact, a response to a much older problem. The problem is the one that the rationalist tradition had set for itself: how is metaphysics possible as a science? Kant’s answer to the question — that metaphysics is possible only as a critique of the powers of reason that make the question intelligible, and that the question of the possibility of metaphysics is, in fact, a more fundamental question than any of the metaphysical questions themselves — was already, in the Inaugural Dissertation of 1770, the doctrine that the Critique would refine. Hume was the occasion. He was not the cause.

The man who wrote the Critique of Pure Reason was, in many respects, an unlikely candidate for the most important philosopher of the modern age. He was the fourth of eleven children of a saddler in Königsberg, in the Prussian province of East Prussia. He was a Privatdozent for fifteen years, until he was appointed to the chair of logic and metaphysics at the University of Königsberg in 1770 at the age of forty-six. He never married. He never traveled more than a hundred miles from Königsberg. The famous story that the citizens set their watches by his afternoon walk is, in its strict form, a legend, but the regularity of his habits — he is said to have walked the same route, in the same order, at the same time, for forty years — is, in its general form, accurate.

The Life

Kant was born on April 22, 1724, in Königsberg, the fourth of eleven children of Johann Georg Kant, a saddler, and Anna Regina Reuter, both of whom were devout members of the German Pietist community that had come to dominate the religious life of Königsberg. The Pietism is, in some ways, the most important fact about Kant’s intellectual formation. The Pietist emphasis on the inner life, on the moral autonomy of the individual, and on the proper relation between faith and works provided the moral framework within which Kant’s mature ethical theory was constructed. The Critique of Practical Reason is, in its central argument, an essay in the ethics of the German Pietist tradition — secularized, of course, and stripped of the specifically Christian doctrine, but recognizably Pietist in its account of the moral life as a struggle between the claims of duty and the claims of inclination.

Kant was educated at the Collegium Fridericianum, a Pietist school in Königsberg, and then at the University of Königsberg, where he studied philosophy, mathematics, and the natural sciences. He was a brilliant student, and his early work was in the natural sciences, particularly in the natural philosophy of Newton. The Universal Natural History and Theory of the Heavens (1755) — the Allgemeine Naturgeschichte — is a remarkable work of speculative cosmology that anticipated, in important ways, the Laplace nebular hypothesis. The work attracted little attention in its time, and the second edition was, in fact, suppressed when Kant’s publisher heard that the work had run afoul of the Prussian censorship.

The decisive decade of his life was the 1770s, the long “silent decade” of intensive intellectual work that produced the Critique of Pure Reason. The first edition appeared in 1781, when Kant was fifty-seven, and the work was, in its initial reception, mostly a failure. The book was long, badly organized, and difficult in a way that no other work of German philosophy had been. The early readers — Mendelssohn, the Göttingen philosopher Feder, the Wolffian school of the German universities — found it impossible to read, and the first serious engagement with the Critique did not come until the early 1780s, with the publication of the Prolegomena to Any Future Metaphysics (1783) and of the Groundwork of the Metaphysics of Morals (1785).

The 1780s and 1790s were the period of the three Critiques, of the Critique of Practical Reason (1788), the Critique of Judgment (1790), and of the long series of essays on political and historical questions. The most famous of these essays is What Is Enlightenment? (1784), the canonical statement of the Enlightenment’s self-understanding. The last decade of his life was the period of the Religion within the Limits of Reason Alone (1793), the famous conflict with the Prussian censorship over the use of natural theology in academic instruction, and the Metaphysics of Morals (1797). He died in Königsberg on February 12, 1804, at the age of seventy-nine, and was buried in the cathedral, in a side chapel of the north aisle, in a tomb that has since been the object of a small but determined scholarly cult.

The Copernican Revolution

The Critique of Pure Reason is Kant’s most important and most difficult work. The argument is, in its central move, a kind of inversion of the older empiricist and rationalist traditions. The rationalist tradition, from Descartes to Wolff, had held that the mind is a passive recipient of knowledge, and that the objects of knowledge are known because the mind conforms to them. The empiricist tradition, from Locke to Hume, had held that the mind is an active processor of sense-data, but that the basic structure of the world is given by the senses. Kant’s argument is that the older traditions were, in fact, the same: both supposed that the mind is, in the strict sense, determined by the objects of knowledge. The argument of the Critique is that the relationship is, in fact, the reverse — that the objects of experience conform to the structure of the mind, and that the mind is, in this sense, the active source of the basic structure of experience.

The argument is the famous “Copernican Revolution” of philosophy. Kant compares it to the change in astronomy from the Ptolemaic to the Copernican system: just as Copernicus showed that the apparent motion of the heavens is, in fact, the result of the motion of the observer, so Kant shows that the apparent passivity of the mind is, in fact, the result of the activity of the mind. The mind is, in this sense, the active source of the basic structure of experience.

The argument is supported by a careful analysis of the nature of human knowledge. Kant distinguishes between the “matter” of knowledge, which is provided by the senses, and the “form,” which is provided by the mind itself. The forms of sensibility are space and time — the pure forms of intuition that structure all our sensory experience, and that are, in Kant’s argument, a priori forms of the mind rather than features of the world. The forms of the understanding are the categories — substance, causation, reciprocity, and the like — that structure the conceptual organization of experience. The mind is, in this sense, the active source of the basic structure of experience, and the world as we know it is the world as structured by the mind.

The argument has implications for the traditional problems of metaphysics. The existence of God, the immortality of the soul, and the freedom of the will are not, for Kant, susceptible to the kind of rational proof that the metaphysical tradition had attempted. They are “ideas of reason” — concepts that have a regulative use in our thinking, but that cannot be objects of theoretical knowledge. The thing in itself, the world as it is independent of our ways of knowing it, is in principle unknowable by the human mind. The critique of the pretensions of speculative metaphysics is one of the central achievements of the critical philosophy.

The argument has been the basis of modern philosophy since 1781, and the scholarly literature on it is enormous. The standard interpretive debate — between the “two-world” reading of the first edition, the “two-aspect” reading of the second edition, and the various attempts to find a third position — has been the basis of a thousand academic careers. The current state of the debate, in the work of Henry Allison, of Rüdiger Bubner, of the late Lewis White Beck, of the late J. N. Findlay, and of the more recent work of Lucy Allais, is that the argument of the first and second editions is, in fact, the same argument — that the A and B editions of the Critique are, in their central doctrines, consistent, and that the apparent differences are matters of emphasis rather than substance. The argument is well advanced, but it is not closed.

The Moral Philosophy

The Critique of Practical Reason (1788) is the most accessible of the three Critiques and the one in which the moral argument is, in fact, the strongest. The central claim is that the foundations of morality are to be found not in the consequences of actions, not in the sentiments or feelings of human beings, but in the very nature of practical reason itself.

The argument is the famous doctrine of the categorical imperative. The categorical imperative is the supreme principle of morality, and it has several formulations. The most famous is the universal-law formulation: “Act only according to that maxim by which you can at the same time will that it should become a universal law.” The principle distinguishes moral actions from merely prudential or instrumental ones. A moral action is one that is done from a maxim that the agent can rationally will to be a universal law of nature.

The argument is rigorous, demanding, and sometimes austere. Kant insists that moral worth requires that actions be done from duty, not from inclination; from respect for the moral law, not from the hope of reward or the fear of punishment. The good will, he famously argues, is the only thing that is good without qualification, and the proper task of morality is to act from good will even when the consequences of doing so are painful or disappointing.

The rigorism of Kant’s moral philosophy has been controversial from the moment of its publication. The famous attack by Schiller — the “sad duty” with which the Kantian moralist is said to greet the man who has lost at cards — captures the common criticism. The defenders — most recently Allen Wood, in his Kantian Ethics (2008), and the late Christine Korsgaard, in her The Sources of Normativity (1996) — have argued that the rigorism is, in fact, the point. The proper response to the Schiller parody is that the moral life is not, in fact, a matter of “sad duty” but a matter of the right kind of will, and that the right kind of will is the one that acts from the moral law for its own sake.

The most influential of Kant’s moral doctrines in the contemporary revival is, in fact, the doctrine of the formula of humanity: “Act in such a way that you treat humanity, whether in your own person or in the person of any other, always at the same time as an end and never merely as a means.” The doctrine is the basis of the contemporary Kantian ethics of human rights, of the Kantian defense of the inviolability of the person, and of the modern doctrine of human dignity. The contemporary revival — most influentially in the work of the late John Rawls, whose A Theory of Justice (1971) was, in its central argument, an essay in Kantian moral philosophy — has done a great deal to bring the rigorism back into the mainstream of ethical thought.

The Critique of Judgment

The Critique of Judgment (1790) is the most under-read of the three Critiques and, in the judgment of the most recent scholarship, the most original. The first part of the book is devoted to aesthetic judgment, the second to teleological judgment — the kind of judgment involved in our understanding of the purposiveness of nature.

The theory of the beautiful is one of the most important in the history of aesthetics. Kant argues that aesthetic judgment — the judgment that something is beautiful or sublime — is disinterested, universal, and necessary. When we judge a natural object or a work of art to be beautiful, we are not interested in its practical use or its personal associations; we are judging it in a way that is disinterested. Yet the judgment claims universal validity, and it requires the agreement of others. The feeling of the beautiful is, in this sense, a “subjective universality.”

The theory of the sublime is one of Kant’s most original contributions. He distinguishes between the mathematical sublime — the experience of the vastness of nature, of the kind that one has in the presence of the starry heavens — and the dynamical sublime — the experience of the power of nature, of the kind that one has in the presence of a thunderstorm or a vast waterfall. In both cases, the experience of the sublime involves a feeling of the inadequacy of the imagination to grasp the object, combined with a feeling of the adequacy of reason to think the idea of totality or omnipotence. The sublime is, in this sense, a “pleasure that arises from the very fact that we are in pain.”

The second part of the Critique — the theory of teleological judgment — is the part in which Kant addresses the problem of the apparent purposiveness of nature. The argument is that the proper use of teleological concepts in biology is a regulative principle of reason, not a constitutive principle of nature. The proper inference from the purposiveness of an organism is not that it was, in fact, designed, but that it must be studied as if it were designed. The argument was, in its day, an important contribution to the philosophy of biology. It is, in our day, mostly of historical interest.

The Political and Historical Writings

Kant’s short essays on political and historical questions are among the most influential works of modern political thought. The 1784 essay Idea for a Universal History with a Cosmopolitan Aim is one of the founding texts of the modern philosophy of history. Kant argues that the apparent purposelessness of human action conceals a deeper purpose: the gradual development of the perfect civil constitution, the development of the cosmopolitan order that will eventually bring peace among nations. The argument is a kind of secularized theodicy. Kant does not believe in a divine providence, but he believes that the natural conflict of human passions and interests can be made to serve the long-term development of human rationality. The “unsocial sociability” of human beings — their tendency both to cooperate and to compete — is, in this sense, the engine of historical progress.

The 1795 essay Perpetual Peace is the most famous of the political writings. Kant proposes six preliminary articles and three definitive articles for the establishment of perpetual peace among nations. The preliminary articles include the abolition of standing armies, the non-interference of one state in the affairs of another, and the gradual abolition of the debt instruments that finance war. The definitive articles include the republican constitution of states, the federation of free states, and the cosmopolitan right of individuals to be treated as citizens of a universal community of human beings.

The essay is one of the founding documents of the modern peace movement, and it is the immediate ancestor of the contemporary project of international law, of international institutions, and of the peaceful resolution of conflicts. The contemporary relevance of the essay is, in fact, one of the more surprising facts of the philosophical reception. Kant’s argument about the federation of free states has been the basis of the contemporary doctrine of collective security; his argument about cosmopolitan right has been the basis of the contemporary doctrine of universal human rights; and his argument about the republican constitution of states has been the basis of the contemporary doctrine of democratic peace.

The 1784 essay What Is Enlightenment? is the canonical statement of the Enlightenment’s self-understanding. Kant defines the Enlightenment as “man’s emergence from self-imposed immaturity,” and he identifies its motto as “Sapere aude” — “Dare to know.” He distinguishes between the public and the private uses of reason, arguing that while the public use of reason — the use that scholars and writers make of their reason in front of the public — must be completely free, the private use of reason — the use that citizens make of their reason in their official capacities — may legitimately be subject to restrictions. The essay ends with a famous statement of the relationship between the Enlightenment and the political order: “If it is now asked whether we at present live in an enlightened age, the answer is: No, but we do live in an age of enlightenment.” The paradox captures the idea that the Enlightenment is not a state of arrival but a process, and that the proper task of the present generation is to continue the work of rational inquiry and political reform.

A Judgement

Kant is, in the judgment of this writer, the most important philosopher of the modern period, and the most overrated. The two judgments are not contradictory. The first is true because of the Critique of Pure Reason, which is, on any reasonable accounting, the most ambitious work of philosophy in the modern tradition, and which sets the agenda for the subsequent history of European philosophy. The second is true because the Critique is also, in important respects, a failure — a brilliant failure, but a failure nonetheless. The transcendental argument, with its careful distinction between the world of appearance and the thing in itself, was the basis of the German Idealist tradition that followed Kant (Fichte, Schelling, Hegel), and the German Idealist tradition was, in turn, the basis of the nineteenth-century reaction against the Enlightenment. The transcendental argument was, in effect, the seed of the romantic reaction.

The best current work on Kant — by Henry Allison, by the late Lewis White Beck, by Allen Wood, by the late J. N. Findlay, by Rüdiger Bubner, and by Marcus Willaschek — has done a great deal to bring the philosophy back to the center of the contemporary curriculum. The verdict that comes out of this body of work is that Kant is, in fact, a much better philosopher than his reputation allows in the Anglo-American tradition, and that the proper response to the Critique of Pure Reason is not the romantic reaction but a careful re-reading of the argument that the transcendental idealism was, in fact, an attempt to solve. The argument is well advanced. It is not yet closed.

The enduring significance of Kant’s philosophy lies, in this writer’s judgment, in the combination of intellectual rigor, moral seriousness, and political engagement. Kant was a defender of human dignity, an advocate of international peace, and a champion of the freedom of inquiry. His works remain a basic reference for any serious engagement with the questions of knowledge, morality, and the human condition. The most lasting of his contributions is, in fact, the moral philosophy — the rigorism, the formula of humanity, the doctrine of human dignity — which has been the basis of the contemporary revival of Kantian ethics in the work of John Rawls, of Christine Korsgaard, of Onora O’Neill, and of the many contemporary moral philosophers who have made the Kantian tradition a central part of the contemporary ethical curriculum.