Immanuel Kant is probably the most important
philosopher of the past 2,000 years, yet he lived a remarkably boring
life. He was born, lived, and died in the provincial Prussian university town
of Königsberg (now Kaliningrad in Russia). He was so regular in
his habits that locals set their clocks by his afternoon walk. Kant
was the first great modern philosopher to be a university man and
spent his entire student and professional life at the University
of Königsberg.
Kant studied the rationalist metaphysicians, such as Leibniz
and Christian Wolff, who were fashionable at the time, as well as
mathematics and physics, in particular the physics of Isaac Newton.
In his early career, he published mainly in the field of natural
science, and he mostly accepted the rationalist metaphysics he had
been taught. He became a full professor in 1770, and for the next
ten years he published nothing, as he painstakingly worked out his mature
philosophy. During this time, he studied the works of David Hume
carefully, and he credited Hume with awakening him from the “dogmatic
slumber” that had kept him from questioning rationalist metaphysics.
In 1781, Kant published his Critique of Pure Reason,
a long and very difficult volume that was met with great interest
and criticism. To this day, it remains one of the most discussed
and influential works in philosophy. Kant continued to write prolifically
throughout the 1780s, publishing almost all of his most important
works in that decade: the Prolegomena to Any Future Metaphysics in
1783, the Groundwork for the Metaphysic of Morals in
1785, the Critique of Practical Reason in 1788,
and the Critique of Judgment in 1790. Kant continued
to think and write well into his old age, and he was at work on
a fourth Critique at the time of his death in 1804.
Kant lived near the end of the Enlightenment, a European
cultural movement that spanned the eighteenth century. Enlightenment
figures such as Voltaire and David Hume sought to replace the traditions
and superstitions of religion and monarchy with a worldview that
relied primarily on the powers of reason. Kant’s work belongs to
this tradition. His three Critiques investigate
the scope and powers of reason and emphasize that the proper study
of metaphysics is our own rational faculties, not the sort of theological questions
that occupied earlier generations.
The Enlightenment drew from, and furthered, the development of
the new science that had begun during the Renaissance and inspired
the republican revolutions in France and America. Kant was at his
most productive around the time of these two great revolutions,
but as he spent his entire life in eastern Prussia, he was largely
untouched by the world events unfolding around him. Nevertheless,
he wrote a number of important essays on political questions, particularly
one discussing the possibility of perpetual peace.
Kant is generally credited with effecting a synthesis
between the empiricist philosophy that had dominated Great Britain
and the rationalist philosophy that had dominated the European continent for
the previous 150 years. Although he was trained in the rationalist
tradition, Kant was heavily influenced by the empiricist philosophy
of David Hume.
The great rationalist philosophers who preceded Kant include René
Descartes, Baruch Spinoza, and Gottfried Wilhelm Leibniz. Rationalism
emphasizes the power of reason to provide answers to metaphysical
and other questions unaided by experience. Descartes’ Meditations famously
begins with the meditator systematically doubting all sensory experience,
then building a rational foundation for knowledge beginning with
the observation, “I think, therefore I am.” While rationalist philosophers
were deeply interested in the new developments in science of the
seventeenth century, they place a far greater emphasis than the
empiricists did on the potential of the unaided intellect.
Empiricism, on the other hand, places a greater emphasis
on sensory experience. In his Essay Concerning Human Understanding, John
Locke argues that the human mind is a tabula rasa,
or blank slate, at birth and that all our knowledge comes from experience, either
directly or by generalizing from experience. George Berkeley and
David Hume add further twists to empiricism, but they remain united
in their hostility to the sort of rationalist metaphysics that attempts
to unravel the nature of God, causation, time, and space by means
of rational argument alone.
Hume is particularly important to this story, as it is
Hume whom Kant credits with making Kant question some of the fundamental tenets
of rationalism. Hume famously argues that our belief in causation
is not rationally justified. He begins by distinguishing between
two kinds of knowledge: “matters of fact,” the empirical knowledge
we derive from sensory experience, and “relations of ideas,” such
as mathematical and logical knowledge, which we cannot deny without
contradiction. He then asks how we can know that one event will
cause another, or more broadly, how we can make any predictions
about the future. We might argue that we can make such predictions
based on past sensory experience: having experienced the sunrise
every morning of our lives, we can predict that it will rise tomorrow
morning as well. However, this prediction draws not just on past
sensory experience but also on the assumption that future events
will bear the same regularity as past events. Hume questions how
we can know this “uniformity principle,” which guarantees that past
sensory experience is a reliable guide to future sensory experience.
He answers that we cannot: this uniformity principle is not a relation
of ideas, since we can deny it without contradicting ourselves,
and it is not a matter of fact, since it deals with future experience,
not past experience.
By questioning our ability to rationally justify causation,
Hume throws a great deal of rationalist metaphysics into doubt.
Kant was impressed with Hume’s work but not entirely ready to abandon rationalism.
The mature philosophy we find in Kant’s Critiques is his
attempt to answer Hume’s skepticism. This answer generates what
Kant calls a “Copernican revolution” in philosophy: both in morals
and in metaphysics, Kant turns his philosophical eye inward, investigating
or critiquing the powers of the human intellect itself. Instead
of asking what we can know, Kant asks how we can know what we can
know.
Kant’s influence has been immense. No philosopher since
Kant has remained entirely untouched by his ideas. Even when the
reaction to Kant is negative, he is the source of great inspiration.
German idealism, which arose in the generation after Kant, draws heavily
on Kant’s work even as it rejects some of his central ideas. Similarly,
the tradition of analytic philosophy, which has dominated the English-speaking
world for the past century, takes its start from Gottlob Frege’s
criticisms of Kant.
