Kant’s Copernican Revolution: Phenomena, Noumena, and Transcendental Idealism
Kant’s Copernican Revolution
The Shift in Epistemology
Kant’s Copernican Revolution draws an analogy between his philosophy and the astronomical shift initiated by Copernicus. Just as Copernicus realized that understanding celestial motion required placing the sun, not the Earth, at the center of the universe, Kant argued that understanding knowledge requires a similar shift. Pre-Kantian philosophy viewed the knower as passive, receiving knowledge from the known object. This model, Kant argued, could explain empirical knowledge but not synthetic a priori knowledge—knowledge that precedes experience. Kant proposed reversing this relationship, suggesting that the knower actively shapes reality in the act of knowing. We can understand synthetic a priori knowledge, he argued, by acknowledging that objects conform to the structure of our minds, not the other way around. We can know a priori, for instance, that any experienced triangle will possess certain geometric properties, not because of the triangle itself, but because these properties are a consequence of our cognitive faculties. Kant summarized this idea by stating that we can only know a priori of things what we ourselves put into them.
Transcendental Idealism and the Illusion of Reason
This revolution leads to Transcendental Idealism: we only know phenomena (appearances), not things-in-themselves (noumena). Kant identifies a “transcendental illusion”: the belief that we can extend our understanding beyond sensory experience to grasp noumena. This illusion, he argues, is as inevitable as the moon appearing larger on the horizon. The Transcendental Dialectic, part of Kant’s Critique of Pure Reason, aims to expose this illusion, not to eliminate it, but to understand its deceptive nature. The illusion arises from applying subjective principles to objective knowledge, a natural and inevitable tendency.
The Categorical Imperative
Kant’s ethics centers on the categorical imperative, the principle that dictates how a rational will ought to act. Unlike hypothetical imperatives, which are conditional, the categorical imperative is unconditional and necessary. It is the law of practical reason, prescribing not what to do, but how to act. Kant offers several formulations of the categorical imperative:
- Act only according to that maxim whereby you can at the same time will that it should become a universal law.
- Act as if the maxim of your action were to become through your will a universal law of nature.
- Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end.