Immanuel Kant

Immanuel Kant spent nearly his entire life in Königsberg, the capital of East Prussia, where he studied, taught, and eventually held a professorship. He was born into a Pietist family, attended the University of Königsberg, and worked for several years as a private tutor before entering academic life. His published work developed during an era shaped by the Scientific Revolution, Newtonian physics, the Enlightenment, and disputes between rationalism and empiricism.¹

Kant’s early writings addressed natural science and metaphysics, including a speculative account of the formation of the solar system later associated with the Kant–Laplace nebular hypothesis. In the 1770s and 1780s he turned decisively toward the problems of knowledge and reason that define his mature philosophy. The first edition of the Critique of Pure Reason appeared in 1781, followed by a substantially revised second edition in 1787.²

Kant’s central claim is that knowledge depends on both sensory experience and forms supplied by the mind. In the Critique of Pure Reason, he argues that space and time are forms through which humans receive appearances, while concepts such as causality help organize those appearances into intelligible experience. These conditions are not learned from individual observations; they make coherent observation possible in the first place.¹

This position, often called transcendental idealism, distinguishes phenomena—objects as experienced—from noumena, or things considered independently of the conditions of human experience. Kant did not simply deny an external world. Rather, he maintained that theoretical reason cannot know things as they are apart from possible experience. His analysis also limits traditional metaphysics: arguments about the soul, the universe as a whole, and God may expose reason’s boundaries, but they cannot establish theoretical knowledge of supersensible objects.³

Kant’s moral philosophy makes rational autonomy the basis of obligation. In the Groundwork of the Metaphysics of Morals and the Critique of Practical Reason, he presents the categorical imperative: a moral principle that binds regardless of personal desire or advantage. One formulation requires people to act only on principles they could will as universal laws; another requires treating humanity, in oneself and others, always as an end and never merely as a means.⁴

For Kant, a good will is morally valuable because it acts from duty, not merely because it produces desirable consequences. His account of freedom is connected to this responsibility: moral agency requires the capacity for rational self-legislation. In political writings such as Toward Perpetual Peace, he defended republican government, lawful international relations, and a cosmopolitan ideal of right. His political thought influenced later theories of human rights and international order, although some claims in his anthropology and writings on race are now recognized as seriously objectionable and incompatible with his universalist moral principles.⁵

Kant’s Critique of Judgment connects his theories of nature and freedom through judgments of beauty, the sublime, and purposiveness. He described beauty as involving “disinterested” pleasure and a claim to shared validity without relying on a determinate concept. The sublime, by contrast, arises when imagination confronts overwhelming magnitude or power and reason recognizes its own superiority to sensuous limitation.⁶

Less familiar aspects of Kant’s career include his extensive teaching of geography and anthropology, his interest in education and natural history, and his role as a public intellectual who wrote on history, religion, and the Enlightenment. His essay “What Is Enlightenment?” defined enlightenment as humanity’s emergence from self-imposed immaturity and urged the public use of reason. Kant’s influence extends beyond philosophy into legal theory, theology, aesthetics, political thought, and modern debates about the limits of scientific explanation.²

• His philosophy is often divided into a pre-critical period and a critical period.
• The term “Copernican revolution” describes his proposal that objects of knowledge conform, in part, to the structures of cognition.
• His rigorous daily routine became famous, but many anecdotes about it were recorded by others and should not be treated as precise biography.

Transcendental idealism

Kant’s view that human experience is structured by forms and concepts supplied by cognition, while things considered independently of experience remain unknowable to theoretical reason.

Categorical imperative

A principle of morality that commands unconditionally, independently of a person’s desires or purposes.

Phenomenon

An object or event as it appears within the conditions of possible human experience.

Noumenon

A thing considered apart from sensory appearance; for Kant, it marks a limit of theoretical knowledge rather than an object that can be directly known.