Find Enlightenment

Kant's Copernican Turn
by Diana Mertz Hsieh

Date: 8 Feb 95
Forum: Washington University in St-Louis, Kant and 19th Century Philosophy class
Copyright: Diana Mertz Hsieh

In the Prolegomena, Kant introduces a whole new method of doing philosophy, particularly metaphysics, which radically influenced all subsequent philosophy. Kant's paradigm shift is the "Copernican Turn," which abandons study of (unknowable) reality-in-itself in favor of inquiry into the world-of-appearances and the innate structures of the mind that determine the nature of experience. According to Kant, only through an account of the a priori principles of the mind can knowledge be validated and objective, and thus lead to metaphysics as science, i.e. as an accepted body of knowledge.

Kant calls his paradigm shift the "Copernican Turn" because he hopes to accomplish, in metaphysics, the same sort of shift in perspective that Copernicus accomplished in astronomy. As Kant explains in the preface to the Critique of Pure Reason, Copernicus resolved the problem of the explaining the movements of the heavenly bodies by rejecting the assumption that the Earth was motionless. Similarly, in metaphysics, Kant rejects the idea that reality is knowable-in-itself and that our experiences conform to the world, and adopts the view that the mind largely determines the nature of our experiences. In other words, Kant states holds that objects conform to our knowledge, thus rejecting the traditional view that knowledge conforms to objects in the world. But unlike Copernicus, Kant rejects the traditional view of cognition because he wants to avoid Humean skepticism and Berkelean idealism, not because of empirical data which contradicts the traditional view.

In order to better grasp the nature of Kant's Copernican Turn, it is important to understand the views that he was rejecting: the skepticism of Hume, the arbitrary assertions of contemporary metaphysicians, and the idealism of Berkeley. Kant was primarily focussed on refuting the skepticism of Hume, and thus with rejecting the premises that inevitably lead to Hume's conclusion that, for example, the law of cause and effect couldn't be proven philosophically. In rejecting these Humean premises, Kant rejects the arbitrary claims of his contemporaries on the true nature of the soul and God. But Kant also does not want to commit himself to Berkelean idealism, and in avoiding it, often commits himself to an untenable position within his own model of metaphysics.

Hume's skepticism was the product of the view that the general principles of metaphysics were based on experience, i.e. on "matters of fact," and hence subject to the uncertainty of induction. Hume held that these principles of metaphysics were "matters of fact" rather than "relations of ideas" because the truth value of the assertions made in metaphysics could not be determined simply be examining the concepts. Because these principles of metaphysics were empirical, they could not be proven until the validity of induction was demonstrated, and so these metaphysical ideas could not be proven philosophically, despite our habitual use of them.

Kant's primary means of refuting Hume is the introduction of the distinction between a priori/a posteriori and analytic/synthetic judgments, which enabled Kant to claim the possibility of the existence of synthetic statements a priori, which would serve as the principles of a science of metaphysics. So in the Prolegomena, after introducing the analytic/synthetic distinction (as separate from the a priori/a posteriori distinction), Kant indicates that a proper metaphysics could only be composed of synthetic judgments a priori, because only such judgments would both have real content and be absolutely certain. In doing so, Kant 'turns' the focus metaphysics to the innate structures and principles of the human mind which determine the character of experience and validate the principles of metaphysics, rather than on reality-in-itself. Kant then demonstrates that such judgments compose pure mathematics and pure natural science, thereby indicating their possibility, as well as defining a methodology of determining the principles of metaphysics. These principles are a priori because of their necessity; we could not imagine them to be false. For example, the a priori concept of time, which, according to Kant, imposes itself on all of our cognition, is determined to be a priori because we cannot imagine our perceptions not ordered in time. These judgments are synthetic because their truth value cannot be determined solely by an application of the law of contradiction to the constituent concepts. Thus, for example, the law of cause and effect is not a fact about the world of things-in-themselves, but rather pure understanding is constituted in such a way so that we must attribute cause and effect to the world of appearances.

In attributing metaphysical principles to the mind rather than external reality, Kant apparently does avoid Hume's skepticism. But Kant also makes some unjustified claims about reality-in-itself, in order to avoid the idealism of Berkeley. Berkeley claimed, like Locke, that we have direct access only to ideas, not to outside objects, but unlike Locke, Berkeley denied that material objects cause mental ones. Kant wants to avoid this "mystical and visionary idealism"of Berkeley (Prolegomena, 37), and distinguishes his views from traditional idealism in the following passage:

"Idealism consists in the assertion that there are none thinking beings; in all other things we believe are perceived in intuition are nothing but representations in the thinking beings, to which no object external to them in fact corresponds. On the contrary, I say that things as objects of our senses exist outside us are given, but we know nothing of what they may be in themselves, knowing only their appearances, i.e. the representations which they cause in us by affecting our senses." (Prolegomena, 32-33, emphasis added)

But Kant's commitment to the view that the world of things-in-themselves not only exists but also causes the world-of-appearances contradicts his claim that one can never know anything about the world of things-in-themselves. One possible means of getting out of this difficulty is to say that, because the understanding must attribute cause to everything, we must postulate a world of things-in-themselves as the cause of the world of experience. The objective validity necessary to make this claim part of a science of metaphysics could not be established though, because either one must reject the claim that knowledge about things-in-themselves is impossible or disavow the existence of things-in-themselves. The first options, admitting that knowledge about the realm of things-in-themselves is possible, is problematic for Kant, since he regards the failures of metaphysics to be the result of arbitrary postulating about this realm. The second alternative, admitting the possibility that the world of things-in-themselves does not exist, would commit him to the possibility of Berkelean idealism, which would prohibit the possibility of an objective science of metaphysics, since it is impossible to achieve objectivity when sense data is all that exists.

Kant faces a similar problem in his attempted resolution of the contradiction of the third antinomy (that either "there are in the world causes through freedom" or "that there is no freedom but all is nature.") (Prolegomena, 80) Kant holds that these statements are not really contradictory, and are only viewed as such due to a misunderstanding of what each statement is asserting. Kant resolves the contradiction by stating that "if natural necessity is referred merely to appearances and freedom to things in themselves, no contradiction arises if we at the same time admit both kinds of causality, however difficult or impossible it ma y be to make the latter kind conceivable." (Prolegomena, 84) But Kant is once again making an unjustified claim about the nature of things-in-themselves, for if freedom did exist only in the realm of things-in-themselves, we would not at all be aware of it., and if we are aware of freedom, then in must be present in the world of experience.

Because of Kant's frequent claims to more knowledge than he is supposed to have access to, I do not think that he does not accomplish the task of making metaphysics a science. But nevertheless, he did accomplish a Copernican Turn of sorts, since the character and methodology used in philosophy was fundamentally altered by his theories.

Find Enlightenment at