Sartre's "Copernican revolution" is essentially the attempt to formulate at the ontological level what Kant attempted to show at the epistemological level: that the phenomenal world we experience is the resultant of the activity of the forms of cognition upon a primordial "given." The basic similarity between Sartre and Kant which must be kept in mind is that for Sartre the "molding' of phenomenal reality is at the ontological level derivative of and dependent upon the activity of the class="EmphasisTypeItalic ">pour-soi, which both "exists" reality and exists in reality. There are important dissimilarities, however, between the two Copernican revolutions. Kant describes the action of the forms of sensibility and of cognition which ultimately constitute the synthetic unity identified as the phenomenal object. Sartre, on the other hand, is not concerned with deducing the categories or determining how synthetic a priori propositions are possible and valid for experience; rather, he wishes to find out in what way the human reality is a function of two polarities: the en-soi and the pour-soi. By introducing his Copernican revolution and asserting the priority of the pour-soi, Sartre attempts to demonstrate how the dialectic of relationships which hold between the en-soi and the pour-soi is ultimately comprehensible.