Kant: The "Copernican Revolution" in Philosophy

Sandra LaFave


The philosophy of Immanuel Kant (1724-1804) is sometimes called the “Copernican revolution of philosophy” to emphasize its novelty and huge importance. Kant synthesized (brought together) rationalism and empiricism. After Kant, the old debate between rationalists and empiricists ended, and epistemology went in a new direction. After Kant, no discussion of reality or knowledge could take place without awareness of the role of the human mind in constructing reality and knowledge.

Summary of Rationalism

The paradigm rationalist philosophers are Plato (ancient); Descartes, Spinoza, Leibniz (modern).

  1. Don’t trust senses, since they sometimes deceive; and since the “knowledge” they provide is inferior (because it changes).

  2. Reason alone can provide knowledge. Math is the paradigm of real knowledge.

  3. There are innate ideas, e.g., Plato’s Forms, or Descartes’ concepts of self, substance, and identity.

  4. The self is real and discernable through immediate intellectual intuition (cogito ergo sum).

  5. Moral notions are comfortably grounded in an objective standard external to self — in God, or Forms.

Kant says rationalists are sort of right about (3) and (4) above; wrong about (1) and (2). Kant would like (5) to be true.

Summary of Empiricism

The paradigm empiricist philosophers are Aristotle (ancient); Locke, Berkeley, Hume (modern).

  1. Senses are the primary, or only, source of knowledge of world. Psychological atomism.

  2. Mathematics deals only with relations of ideas (tautologies); gives no knowledge of world.

  3. No innate ideas (though Berkeley accepts Cartesian self). General or complex ideas are derived by abstraction from simple ones (conceptualism).

  4. Hume — there’s no immediate intellectual intuition of self. The concept of “Self” is not supported by sensations either.

  5. Hume — no sensations support the notion of necessary connections between causes and effects, or the notion that the future will resemble the past.

  6. Hume — “is” does not imply “ought”. Source of morality is feeling.

Kant thinks empiricism is on the right track re (1), sort of right re (2), wrong re (3), (4), (5), and (6).


Summary of Kant’s Argument
  1. The epistemological debate between rationalism and empiricism is basically about whether, or to what extent the senses contribute to knowledge. Both rationalism and empiricism take for granted that it’s possible for us to acquire knowledge of Reality, or how things really are, as opposed to how they seem to us.

  2. But both rationalism and empiricism overlook the fact that the human mind is limited; it can experience and imagine only within certain constraints. These constraints are both synthetic and a priori. All our possible experience must conform to these SAPs. The SAPs include location in space and time, causality, experiencing self, thing-ness, identity, and various mathematical notions. (Twentieth- century Gestalt psychology’s attack on psychological atomism is based on Kant’s views.)

  3. Therefore, we must distinguish the world we experience, bounded by SAPs, and the world of things as they really are “in themselves”. Kant calls these two worlds the phenomenal (apparent) world versus the noumenal (real) world.

  4. Empiricism pretty much nails what it means to know something, once the SAPs are in place; i.e., within the phenomenal world, empiricism rules. The phenomenal world is a world of things, publicly observable, describable by science, known to the senses, determined by physical laws. No God, no freedom, no soul, no values exist in this world.

  5. If God, freedom, souls, and values exist, then they must be noumenal and unknowable by any ordinary means.

Thus, according to Kant:

  • Both rationalism and empiricism are wrong when they claim that we can know things in themselves.

  • Rationalists are wrong not to trust senses; in the phenomenal world, senses are all we have.

  • Rationalists are right about “innate ideas”, but not in Plato’s sense of Forms — much more like Descartes’ in argument of the wax.

  • Hume is wrong when he claims the concept of self is unsupported by senses, and thus bogus. Rather, the experiencing self is a pre-condition for having any experience at all (Descartes was right).

  • Hume is wrong when he says the notion that the future will resemble the past is due only to “custom and habit”. That notion is a SAP; we couldn’t have ordinary experience without it.

  • Hume is wrong when he says the source of morality is feeling. Morality, properly understood, provides the key to linking the noumenal and phenomenal worlds. Kant argues that if morality is real, then human freedom is real, and therefore humans are not merely creatures of the phenomenal world (not merely things subject to laws).


Ramifications of Kant’s Views

Kant revolutionized philosophy. Kant showed that the mind, through its innate categories, constructs our experience along certain lines (space, time, causality, self, etc.). Thus, thinking and experiencing give no access to things as they really are. We can think as hard as we like, but we will never escape the innate constraints of our minds. Kant forced philosophy to look seriously at the world for the agent (what Kant calls the phenomenal world) independently of the real world outside consciousness – the world in itself (the noumenal world).

Ethics had long recognized the importance for moral evaluation of “how things seem to the agent.” But the ramifications of Kant’s noumenal-phenomenal distinction extend far beyond ethics. Philosophers like to take credit for all the big events in 19th century intellectual history as direct consequences of Kant’s philosophical legitimizing of the perspective of the subject: Hegel and German idealism, Darwinism, Romanticism, pragmatism, Marxism, the triumph of utilitarianism, Nietzsche, and the establishment of psychology as a science, especially Gestalt psychology.



Sample Essay Questions

  1. Modern philosophical rationalism and empiricism ended with Kant. Why?

  2. What would Kant say about psychological atomism (Locke’s view that all knowledge is built from elementary sense data)?

  3. What does Gestalt psychology owe to Kant?



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