Kant's “Copernican Revolution”

Kant noticed a problem with the empiricist manner of coming to knowledge. If all you come to know and collect are particular sensations or particular impressions, as the empiricists said, how can you arrive at necessary and universal knowledge? Put another way, how can you explain the possibility of scientific knowledge, or, more precisely, the relationship between causes and effect, which enables the mind to grasp scientific truths? Kant had an answer to the question that bridges the gap between two schools of thought — rationalism and empiricism.

What personal traits did Kant exhibit?

Immanuel Kant lived a quiet, orderly life, but he enjoyed the company of others. He hardly traveled and he earned a legendary reputation for punctuality. It was said that people could set their clocks by him as he took his early morning walk past their windows.

Kant's own theory of knowledge reconfigures the way humans know things. Rather than saying that people are all passive perceivers observing the world, Kant believed that humans are active in knowing the world. In agreeing with his empiricist predecessors he says, “There can be no doubt that all our knowledge begins with experience. But though all our knowledge begins with experience, it does not follow that it all arises out of experience.”

Instead of an outside-in approach to knowledge of the empiricists, in which objects cause passive perceivers to have “sensations” (Locke) or “impressions” (Hume), Kant said that the categories of space and time — which he called “forms of intuition” — were imposed on experiences by the human mind in order to make sense of it. This Kant proudly called his “Copernican Revolution.” Just as Copernicus rejected the idea that the sun revolved around the earth, Kant had solved the problem of how the mind acquires knowledge from experience by arguing that the mind imposes principles upon experience to generate knowledge.

Kant proposed that the mind has “categories of understanding,” which catalogue, codify, and make sense of the world. The mind cannot experience anything that is not filtered through the mind's eye. Therefore, you can never know the true nature of reality. In this sense, Kant claims that indeed “perception is reality.”

Kant is saying that in order to have any knowledge, the mind needs to have a set of further organizing principles. These principles are found in the faculty of the understanding. Just as a cookie is the product of a certain content (the dough) being processed by a form (the cookie press), so knowledge is the product of content (what you sense) and understanding (space and time as forms of intuition) working together.

In other words, both a priori and a posteriori elements are essential. Without sensation, no object would be perceptible. Without understanding, no object could be conceived. As Kant said in his Critique of Pure Reason, “Thoughts without contents are empty, perceptions without conceptions are blind…. Understanding can perceive nothing, the senses can think nothing. Knowledge arises only from their united action.”

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