The present paper offers a reconstruction of Husserl's understanding of Kant's transcendental philosophy, notably, of the function of the "synthesis of reproduction" in the fi rst edition of the Critique of Pure Reason , based upon a series of 1907-1909 manuscripts now published in Hua VII. After clarifying the wider theoretical framework within which Husserl reads Kant here, the present paper makes the case for holding the distinction between two different forms of rationality (the transcendental rationality and the ontological one), hence their relevant articulation, to be the real issue at the center of Husserl's Auseinandersetzung with the thinker of Königsberg.