It can be said that there was philosophy before Immanuel Kant, and after Immanuel Kant. Before Kant, there was a division in philosophy between rationalists on one side, and empiricists on the other. After Kant, we were left with his self-proclaimed Copernican revolution, and a synthesis of rationalism and empiricism.

Immanuel Kant was born in 1724 to a lower middle class family. His father was a German craftsmen and his mother was Pietist, a movement within the Lutheran Church. He received a strict pietist education, which favored Latin and religious teachings over mathematics and science. Kant enrolled in the University of Konigsberg at age 16 (1740), and studied the rationalist philosophy of Leibniz and Wolff under Martin Knutsen (who was also a rationalist). He published his first work in 1749 (Thoughts on the True Estimation of Living Forces). He published several more scientific works, and in 1755 became a university lecturer. In 1770 (age 45), Kant was appointed Professor of Logic and Metaphysics at the University of Konigsberg. He did not produce another notable work for the next decade or so. In 1781 his Critique of Pure Reason was published, and although it was largely ignored in its first publication, it is now considered one of the greatest works in philosophy. He published a second edition of the book in 1787, in 1788 the Critique of Practical Reason, and the third Critique of Judgment in 1790 (Immanuel Kant).

In Kant’s time, the major school of thought in Germany was that of rationalism. Rationalism was the answer to the questions epistemology raised about the nature of knowledge, its limits, and its validity. Rationalists sought to solve these problems by arguing that it was reason that played the major role in epistemology. Major rationalist thinkers include Rene Descartes, Baruch Spinoza, and Gottfired Wilhelm von Leibniz (Engel). They sought to construct knowledge of the external world, the soul, the self, God, ethics and science, out of the simplest, innately possessed (a priori) ideas of the mind. Descartes believed that certain statements such as “I think therefore, I am” are infallible, even to the most extreme forms of skepticism. He inferred that since he exists, and that since God exists and is not deceiving him about his senses, then objects in space beyond him exist (McCormick). He concluded that the mind and body are separate entities (dualism). Spinoza concluded that the mind and body are part of one substance, or God (monism), and Leibniz that substance was made of basic units called monads (pluralism) (Engel).

For a long time, Kant was a follower of the rationalist school of thought. Sometime between 1756 and 1762, he read a translation of David Hume’s Enquiry Concerning Human Understanding. This work, he said, awoke him from his “dogmatic slumber,” (Engel). David Hume belonged to another major school of thought centered around England, English empiricism. David Hume, John Locke, and George Berkeley argued that knowledge originates in our senses. To sum up the empiricists’ philosophies, Locke said that we are born with a tabula rasa (blank slate) and that “there is nothing in the mind except what was first in the senses.” Since only material things affect our sense, we can know only matter, and must accept a materialist philosophy. Berkeley argued that matter does not exist except as a form of mind. Our knowledge of it is merely sensations of it, and ideas derived from these sensations (an idealist philosophy). “We know the mind only as we know matter.” is what Hume argued. The mind is nothing except sensations, memories, and feelings (skepticism) (Durant). Whereas rationalism ended in dogmatism, empiricism ended in skepticism (Engel).

Immanuel Kant’s major contribution to philosophy is the synthesis of the two major schools of rationalism and empiricism. Kant argued that the positions of Locke, Berkeley, and Hume were flawed because they presupposed the very claims they set out to disprove. He also had his doubts about rationalism because of arguments he called antimonies, or contradictory, but still validly proven pairs of claims that reason makes. An example Kant uses are the claims “The world has a beginning in time and is limited as regards space," and "The world has no beginning, and no limits in space." (McCormick). Kant said that we must recognize that we cannot know things as they are in themselves, and that our knowledge is subject to the conditions of our experience. Rationalism was faulted because it did not take into account the contribution that our faculty of reason makes to our experience of objects. He argued that the division between a priori (prior to experience) and a posteriori (known from experience) was insufficient to explain the claims being made at the time. He also made a distinction between analytic and synthetic truths. An analytic claim is one in which the predicate is contained within the subject. “In the claim, ‘Every body occupies space,’ the property of occupying space is revealed in an analysis of what it means to be a body.” The subject of a synthetic claim does not contain the predicate. “In, ‘This tree is 120 feet tall,’ the concepts are synthesized or brought together to form a new claim that is not contained in any of the individual concepts.” (McCormick)

A large portion of the Critique of Pure reason is devoted to the question “how are synthetic a priori judgments possible?” A claim, such as that of geometry, that “the angles of a triangle always add up to 180 degrees,” is known a priori, but can not be known only through the analysis of the concept of a triangle. We must, as Kant says, "go outside and beyond the concept. . . joining to it a priori in thought something which I have not thought in it." Claims such as “every event must have a cause” can not be proven by experience. Synthetic a priori claims such as this are possible though, because in this claim, “it describes the way the mind must necessarily order its representations.” (McCormick). Kant proposed that it must be the mind’s systematic structuring that made experience possible. He compared this idea of the mind being active in structuring reality to the revolution Copernicus had when he said that it is not the stars that are revolving around the observer, but the observer around the stars. Similarly, instead of the Lockean view that mental content is given to the mind by the objects in the world, and from there the true nature of objects is revealed, the Kantian view held that it is the mind that gives objects at least some of their characteristics, because the objects are first filtered through the “systematic structuring” process of the mind. Kant’s ideas of a priori knowledge are different from the rationalist’s ideas of a priori knowledge, in that the rationalists claimed that a priori ideas were complete propositions such as “God is a perfect being.” Kant’s innate structuring mechanisms had not complete content, but allowed for the synthesis of concepts into judgments. “The mind possesses a priori templates for judgments, not a priori judgments.” (McCormick).

This essay merely scratched the surface of Kant’s teachings. Actually, I only dealt with one part of his Critique of Pure Reason. When speaking of Kant’s Copernican revolution, Will Durant says “If perceptions wove themselves automatically into ordered thought, if mind were not an active effort hammering out order from chaos, how could the same experience leave one man mediocre, and in a more active and tireless soul be raised to the light of wisdom and the beautiful knowledge of truth.” In 1804 Immanuel Kant died due to health problems. Near his tomb is the inscription taken from the conclusion of his Critique of Practical Reason: “Two things fill the mind with ever new and increasing admiration and awe, the more often and perseveringly my thinking engages itself with them: the starry heavens above me and the moral law within me. “