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Immanuel Kant is one of the most influential philosophers in the history of Western philosophy. His contributions to metaphysics, epistemology, ethics, and aesthetics have had a profound impact on almost every philosophical movement that followed him. This portion of the Encyclopedia entry will focus on his metaphysics and epistemology in one of his most important works, The Critique of Pure Reason. (All references will be to the A (1781) and B(1787) edition pages in Werner Pluhar's translation. Indianapolis: Hackett, 1996.) A large part of Kant's work addresses the question "What can we know?" The answer, if it can be stated simply, is that our knowledge is constrained to mathematics and the science of the natural, empirical world. It is impossible, Kant argues, to extend knowledge to the supersensible realm of speculative metaphysics. The reason that knowledge has these constraints, Kant argues, is that the mind plays an active role in constituting the features of experience and limiting the mind's access to the empirical realm of space and time.

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Table of Contents (Clicking on the links below will take you to those parts of this article)

1. Historical Background to Kant

a. Empiricism

b. Rationalism

2. Kant's Answers to his Predecessors

3. Kant's Copernican Revolution: Mind Making Nature

4. Kant's Transcendental Idealism

5. Kant's Analytic of Principles

6. Kant's Dialectic

7. The Ideas of Reason

8. Kant's Ethics

a. Reason and Freedom

b. The Duality of the Human Situation

c. The Good Will

d. Duty

9. Kant's Criticisms of Utilitarianism

10. Sources

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1. Historical Background to Kant

In order to understand Kant's position, we must understand the philosophical background that he was reacting to. First, I will present a brief overview of his predecessor's positions with a brief statement of Kant's objections, then I will return to a more detailed exposition of Kant's arguments. There are two major historical movements in the early modern period of philosophy that had a significant impact on Kant: Empiricism and Rationalism. Kant argues that both the method and the content of these philosophers' arguments contain serious flaws. A central epistemological problem for philosophers in both movements was determining how we can escape from within the confines of the human mind and the immediately knowable content of our own thoughts to acquire knowledge of the world outside of us. The Empiricists sought to accomplish this through the senses and a posteriori reasoning. The Rationalists attempted to use a priori reasoning to build the necessary bridge. A posteriori reasoning depends upon experience or contingent events in the world to provide us with information. That "Bill Clinton is president of the United States in 1999," for example, is something that I can know only through experience; I cannot determine this to be true through an analysis of the concepts of "president" or "Bill Clinton." A priori reasoning, in contrast, does not depend upon experience to inform it. The concept "bachelor" logically entails the ideas of an unmarried, adult, human male without my needing to conduct a survey of bachelors and men who are unmarried. Kant believed that this twofold distinction in kinds of knowledge was inadequate to the task of understanding metaphysics for reasons we will discuss in a moment.

a. Empiricism

Empiricists, such as Locke, Berkeley, and Hume, argued that human knowledge originates in our sensations. Locke, for instance, was a representative realist about the external world and placed great confidence in the ability of the senses to inform us of the properties that empirical objects really have in themselves. Locke had also argued that the mind is a blank slate, or a tabula rasa, that becomes populated with ideas by its interactions with the world. Experience teaches us everything, including concepts of relationship, identity, causation, and so on. Kant argues that the blank slate model of the mind is insufficient to explain the beliefs about objects that we have; some components of our beliefs must be brought by the mind to experience.

Berkeley's strict phenomenalism, in contrast to Locke, raised questions about the inference from the character of our sensations to conclusions about the real properties of mind-independent objects. Since the human mind is strictly limited to the senses for its input, Berkeley argued, it has no independent means by which to verify the accuracy of the match between sensations and the properties that objects possess in themselves. In fact, Berkeley rejected the very idea of mind-independent objects on the grounds that a mind is, by its nature, incapable of possessing an idea of such a thing. Hence, in Kant's terms, Berkeley was a material idealist. To the material idealist, knowledge of material objects is ideal or unachievable, not real. For Berkeley, mind-independent material objects are impossible and unknowable. In our sense experience we only have access to our mental representations, not to objects themselves. Berkeley argues that our judgments about objects are really judgments about these mental representations alone, not the substance that gives rise to them. In the Refutation of Material Idealism, Kant argues that material idealism is actually incompatible with a position that Berkeley held, namely that we are capable of making judgments about our experience.

David Hume pursued Berkeley's empirical line of inquiry even further, calling into question even more of our common sense beliefs about the source and support of our sense perceptions. Hume maintains that we cannot provide a priori or a posteriori justifications for a number of our beliefs like, "Objects and subjects persist identically over time," or "Every event must have a cause." In Hume's hands, it becomes clear that empiricism cannot give us an epistemological