Immanuel Kant (22 April 1724–12 February 1804) was a German philosopher associated with the Enlightenment. His critical philosophy investigated the powers and limits of human reason, reshaping epistemology, metaphysics, and ethics. He argued that experience depends partly on structures supplied by the human mind, while moral obligation rests on rational self-government rather than desire or external authority. His three major Critiques distinguish theoretical knowledge, practical reason, and judgment. (plato.stanford.edu)
Life and intellectual development
Kant was born in Königsberg, Prussia, now Kaliningrad, Russia, and spent his academic career there. Raised in a Pietist household, he studied at the University of Königsberg, worked as a private tutor, and began university teaching in 1755. In 1770 he became professor of logic and metaphysics. His teaching ranged beyond philosophy to physical geography, anthropology, and natural science. (iep.utm.edu)
His early writings addressed scientific and metaphysical problems within an intellectual setting shaped by Gottfried Wilhelm Leibniz and Isaac Newton. He subsequently reconsidered both rationalism and empiricism. David Hume was particularly important: Hume’s challenge to necessary causal connections helped prompt Kant’s investigation of how objectively valid knowledge is possible. Kant’s mature critical project emerged after decades of teaching and publication, rather than as a complete rejection of his earlier interests. (iep.utm.edu)
Knowledge and the limits of reason
The *Critique of Pure Reason* appeared in 1781, with a substantially revised edition in 1787. Kant asks how knowledge can be both informative and necessary. He distinguishes analytic judgments, which explain what is already contained in a concept, from synthetic judgments, which add information. He also distinguishes a priori justification, independent of experience, from empirical justification. His central problem concerns the possibility of synthetic a priori knowledge, which he takes to occur in mathematics and fundamental principles of natural science. (iep.utm.edu)
Kant’s response is that knowing is not merely passive reception. Sensibility supplies intuitions structured by space and time; understanding organizes them through concepts, including categories such as substance and causation. These structures are conditions under which objects can be experienced, not discoveries obtained simply by accumulating observations. Kant compares this change in explanatory direction to a Copernican revolution: objects of possible experience must conform to the conditions of human cognition. (iep.utm.edu)
His transcendental idealism distinguishes objects as they appear under these conditions from things considered independently of them. It does not mean that ordinary objects are illusions: Kant also maintains empirical realism, affirming knowledge of objects in space and time. However, theoretical cognition cannot establish knowledge of things in themselves. Interpreters disagree over whether this distinction concerns two kinds of objects or different ways of considering the same objects. (plato.stanford.edu)
Reason encounters difficulties when it treats the soul, the world as a completed whole, or God as objects of theoretical knowledge. Kant’s critique seeks to explain these difficulties while preserving legitimate empirical inquiry. Restricting theoretical knowledge also leaves room for a practical account of freedom without claiming that freedom has been scientifically demonstrated. (iep.utm.edu)
Moral philosophy
Kant develops his moral theory in the Groundwork of the Metaphysics of Morals (1785), Critique of Practical Reason (1788), and Metaphysics of Morals (1797). His approach is a major foundation of deontological ethics. He distinguishes acting in conformity with duty from acting from duty: an action’s moral worth depends on its motivating principle, not merely its outcome or agreement with an established rule. (plato.stanford.edu)
The categorical imperative is an unconditional requirement of practical reason, unlike hypothetical imperatives that depend on pursuing particular goals. One formulation requires agents to act only on maxims they can rationally will as universal laws. Another requires treating humanity, in oneself and others, always as an end and never merely as a means. This concerns respect for rational agency, not a prohibition on every cooperative use of another person’s services. (plato.stanford.edu)
Autonomy means that a rational will gives itself universally valid moral law; it does not mean inventing private moral standards. Kant connects morality with freedom and distinguishes perfect duties, such as prohibitions on false promising, from imperfect duties, such as beneficence, which allow latitude in their fulfillment. (plato.stanford.edu)
Aesthetics and natural purposes
The Critique of the Power of Judgment (1790) addresses aesthetics and teleology. Kant describes judgments of beauty as grounded in disinterested pleasure: appreciation does not depend on wanting to possess an object or use it. Although such judgments arise from feeling rather than determinate concepts, they claim agreement from others rather than reporting only private preference. He explains this through a free play of imagination and understanding. (plato.stanford.edu)
His account of the sublime concerns experiences of overwhelming magnitude or power and their relation to reason. In discussing organisms, Kant argues that their interconnected parts must be judged as serving the whole. Such purposive judgment guides human understanding without establishing a theoretical proof that nature was designed by an intelligent creator. (plato.stanford.edu)
Politics and reception
In political philosophy, Kant grounds rightful relations in the compatibility of each person’s external freedom with everyone else’s freedom under universal law. His 1784 essay on enlightenment defends public reasoning. Toward Perpetual Peace (1795) proposes republican constitutions, a federation of free states, and cosmopolitan hospitality as conditions for peaceful international relations. These proposals concern juridical institutions, not simply individual goodwill. (plato.stanford.edu)
Kant’s work became a starting point for German idealism and influenced Arthur Schopenhauer. Later philosophers developed or challenged his accounts of cognition, autonomy, and judgment. His writings remain important in both analytic and continental philosophy, while disagreements about transcendental idealism continue to shape interpretations of his system. (plato.stanford.edu)