What makes Immanuel Kant's Copernican revolution Copernican and what makes it a revolution?The B-Preface to the Critique of Pure Reason (1781Reason ( , 1787 proposes an "experiment" that "promises to metaphysics the secure course of a science", viz., to assume, not that "all our cognition must conform to the objects", which is an assumption that "[u]p to now" has "come to nothing", but rather that "objects must conform to our cognition". Kant compares this assumption to "the first thoughts of Copernicus". Just as Copernicus discovers a shift in the nature of celestial bodies on the basis of a "hypothesis" about the orbital activity of the earth, so too Kant discovers a shift in the nature of natural bodies on the basis of an "analogous" hypothesis about the cognitive activity of the subject. Insofar as the subject contributes to cognition both the "representations of space and time" and "the elementary concepts of the understanding", the object must "agree" with these representational elements and so must be cognizable, not as "a thing in itself ", but rather as "an appearance". 1 Kant's Copernican revolution is Copernican, then, because it turns from prioritizing the status of the object toward prioritizing the activity of the subject.The B-Preface also cites Copernicus' theory as a "remarkable" example of sciences that "have become what they are now through a revolution brought about all at once". Kant clarifies that the analogous revolution that he proposes for "the accepted procedure of metaphysics" is firstpersonal, since it amounts to a "transformation in our way of thinking" whereby the idea that "cognition reaches only appearances" serves as a "crosscheck" for our explanation of the possibility of cognition. 2 This change of mind is not unlike what, in Religion Within the Boundaries of Mere Reason (1793), Kant calls a "change of heart", viz., the "transformation" of our moral disposition whereby, through a "revolution" as opposed to a "gradual reform", the "representation of duty" alone becomes our incentive to act. 3 Such a change of heart results from judging, exclusively on the basis of consciousness of the moral law, that "[one] can do something because [one] is aware that [one] ought to do it and cognizes freedom within [oneself ]", as Kant explains in the Critique of Practical Reason (1788). 4 Moreover, a change of mind and a change of heart must be two aspects of one and the same revolution, given that, as Kant says in Groundwork of the Metaphysics of Morals (1785), a "complete critique of reason" must transform our reason in both its theoretical and its practical uses. 5 Kant's Copernican revolution is a revolution, then, because it demands a transformation of oneself.