Immanuel (1724–1804), preeminent German philosopher whose distinctive concern was to vindicate the authority of reason. He believed that by a critical examination of its own powers, reason can distinguish unjustifiable traditional metaphysical claims from the principles that are required by our theoretical need to determine ourselves within spatiotemporal experience and by our practical need to legislate consistently with all other rational wills. Because these principles are necessary and discoverable, they defeat empiricism and skepticism, and because they are disclosed as simply the conditions of orienting ourselves coherently within experience, they contrast with traditional rationalism and dogmatism. Kant was born and raised in the eastern Prussian university town of Königsberg (today Kaliningrad), where, except for a short period during which he worked as a tutor in the nearby countryside, he spent his life as student and teacher. He was trained by Pietists and followers of Leibniz and Wolff, but he was also heavily influenced by Newton and Rousseau. In the 1750s his theoretical philosophy began attempting to show how metaphysics must accommodate as certain the fundamental principles underlying modern science; in the 1760s his practical philosophy began attempting to show (in unpublished form) how our moral life must be based on a rational and universally accessible self-legislation analogous to Rousseau’s political principles. The breakthrough to his own distinctive philosophy came in the 1770s, when he insisted on treating epistemology as first philosophy. After arguing in his Inaugural Dissertation (On the Form and Principles of the Sensible and Intelligible World, 1770) both that our spatiotemporal knowledge applies only to appearances and that we can still make legitimate metaphysical claims about ‘intelligible’ or non-spatiotemporal features of reality (e.g., that there is one world of substances interconnected by the action of God), there followed a ‘silent decade’ of preparation for his major work, the epoch-making Critique of Pure Reason (first or ‘A’ edition, 1781; second or ‘B’ edition, with many revisions, 1787; Kant’s initial reaction to objections to the first edition dominate his short review, Prolegomena to any Future Metaphysics, 1783; the full title of which means ‘preliminary investigations for any future metaphysics that will be able to present itself as a science’, i.e., as a body of certain truths). This work resulted in his mature doctrine of transcendental idealism, namely, that all our theoretical knowledge is restricted to the systematization of what are mere spatiotemporal appearances. This position is also called formal or Critical idealism, because it criticizes theories and claims beyond the realm of experience, while it also insists that although the form of experience is ideal, or relative to us, this is not to deny the reality of something independent of this form. Kant’s earlier works are usually called pre-Critical not just because they precede his Critique but also because they do not include a full commitment to this idealism.
Kant supplemented his ‘first Critique’ (often cited just as ‘the’ Critique) with several equally influential works in practical philosophy – Groundwork of the Metaphysics of Morals (1785), Critique of Practical Reason (the ‘second Critique,’ 1788), and Metaphysics of Morals (consisting of ‘Doctrine of Justice’ and ‘Doctrine of Virtue,’ 1797). Kant’s philosophy culminated in arguments advancing a purely moral foundation for traditional theological claims (the existence of God, immortality, and a transcendent reward or penalty proportionate to our goodness), and thus was characterized as ‘denying knowledge in order to make room for faith.’ To be more precise, Kant’s Critical project was to restrict theoretical knowledge in such a way as to make it possible for practical knowledge to reveal how pure rational faith has an absolute claim on us. This position was reiterated in the Critique of Judgment (the ‘third Critique,’ 1790), which also extended Kant’s philosophy to aesthetics and scientific methodology by arguing for a priori but limited principles in each of these domains. Kant was followed by radical idealists (Fichte, Schelling), but he regarded himself as a philosopher of the Enlightenment, and in numerous shorter works he elaborated his belief that everything must submit to the ‘test of criticism,’ that human reason must face the responsibility of determining the sources, extent, and bounds of its own principles. The Critique concerns pure reason because Kant believes all these determinations can be made a priori, i.e., such that their justification does not depend on any particular course of experience (‘pure’ and ‘a priori’ are thus usually interchangeable). For Kant ‘pure reason’ often signifies just pure theoretical reason, which determines the realm of nature and of what is, but Kant also believes there is pure practical reason (or Wille), which determines a priori and independently of sensibility the realm of freedom and of what ought to be. Practical reason in general is defined as that which determines rules for the faculty of desire and will, as opposed to the faculties of cognition and of feeling. On Kant’s mature view, however, the practical realm is necessarily understood in relation to moral considerations, and these in turn in terms of laws taken to have an unconditional imperative force whose validity requires presuming that they are addressed to a being with absolute freedom, the faculty to choose (Willkür) to will or not to will to act for their sake. Kant also argues that no evidence of human freedom is forthcoming from empirical knowledge of the self as part of spatiotemporal nature, and that the belief in our freedom, and thus the moral laws that presuppose it, would have to be given up if we thought that our reality is determined by the laws of spatiotemporal appearances alone. Hence, to maintain the crucial practical component of his philosophy it was necessary for Kant first to employ his theoretical philosophy to show that it is at least possible that the spatiotemporal realm does not exhaust reality, so that there can be a non-empirical and free side to the self. Therefore Kant’s first Critique is a theoretical foundation for his entire system, which is devoted to establishing not just (i) what the most general necessary principles for the spatiotemporal domain are – a project that has been called his ‘metaphysics of experience’ – but also (ii) that this domain cannot without contradiction define ultimate reality (hence his transcendental idealism). The first of these claims involves Kant’s primary use of the term ‘transcendental’, namely in the context of what he calls a transcendental deduction, which is an argument or ‘exposition’ that establishes a necessary role for an a priori principle in our experience. As Kant explains, while mathematical principles are a priori and are necessary for experience, the mathematical proof of these principles is not itself transcendental; what is transcendental is rather the philosophical argument that these principles necessarily apply in experience. While in this way some transcendental arguments may presume propositions from an established science (e.g., geometry), others can begin with more modest assumptions – typically the proposition that there is experience or empirical knowledge at all – and then move on from there to uncover a priori principles that appear required for specific features of that knowledge.
Kant begins by connecting metaphysics with the problem of synthetic a priori judgment. As necessary, metaphysical claims must have an a priori status, for we cannot determine that they are necessary by mere a posteriori means. As objective rather than merely formal, metaphysical judgments (unlike those of logic) are also said to be synthetic. This synthetic a priori character is claimed by Kant to be mysterious and yet shared by a large number of propositions that were undisputed in his time. The mystery is how a proposition can be known as necessary and yet be objective or ‘ampliative’ or not merely ‘analytic.’ For Kant an analytic proposition is one whose predicate is ‘contained in the subject.’ He does not mean this ‘containment’ relation to be understood psychologically, for he stresses that we can be psychologically and even epistemically bound to affirm non-analytic propositions. The containment is rather determined simply by what is contained in the concepts of the subject term and the predicate term. However, Kant also denies that we have ready real definitions for empirical or a priori concepts, so it is unclear how one determines what is really contained in a subject or predicate term. He seems to rely on intuitive procedures for saying when it is that one necessarily connects a subject and predicate without relying on a hidden conceptual relation. Thus he proposes that mathematical constructions, and not mere conceptual elucidations, are what warrant necessary judgments about triangles. In calling such judgments ampliative, Kant does not mean that they merely add to what we may have explicitly seen or implicitly known about the subject, for he also grants that complex analytic judgments may be quite informative, and thus ‘new’ in a psychological or epistemic sense. While Kant stresses that non-analytic or synthetic judgments rest on ‘intuition’ (Anschauung), this is not part of their definition. If a proposition could be known through its concepts alone, it must be analytic, but if it is not knowable in this way it follows only that we need something other than concepts. Kant presumed that this something must be intuition, but others have suggested other possibilities, such as postulation. Intuition is a technical notion of Kant, meant for those representations that have an immediate relation to their object. Human intuitions are also all sensible (or sensuous) or passive, and have a singular rather than general object, but these are less basic features of intuition, since Kant stresses the possibility of (nonhuman) non-sensible or ‘intellectual’ intuition, and he implies that singularity of reference can be achieved by non-intuitive means (e.g., in the definition