 In the transcendental argument of the Refutation of Idealism, Kant’s target is not Humean skepticism about the applicability of a priori concepts, but rather Cartesian skepticism about the external world. This argument was added by Kant to the second edition of the Critique of Pure Reason (B274–279, with a change suggested in the Preface to B, Bxxxix–Bxli), and subsequently embellished and reworked in a series of Reflections (Guyer 1987: 279–316). More specifically, Kant intends to refute what he calls problematic idealism, according to which the existence of objects outside us in space is “doubtful and indemonstrable” (B274). His strategy is to derive the claim that such objects exist from my awareness that my representations have a specific temporal order. At the present time I am aware of the specific temporal order of many of my past experiences, an awareness produced by memory. But what is it about what I remember that allows me to determine the temporal order of my experiences? There must be something by reference to which I can correlate the remembered experiences that allows me to determine their temporal order. But first, I have no conscious states that can play this role. Further, this reference cannot be time itself, for “time by itself is not perceived;” Kant argues for this claim in the First Analogy (B224–5). As Guyer puts it, it is not as if the content of memories of individual events are manifestly indexed to specific times, as sportscasts and videotapes often are (Guyer 1987: 244). Kant contends that the only other candidate for this reference is something outside of me in space, and it must be something (relatively) permanent (cf. First Analogy, B224–5). Perhaps this claim is made plausible by how we often actually determine the times at which our experiences occur. We use observations of sun’s positions, or of a clock that indicates time by way of the period of a pendulum, or by the period of the vibration of a cesium atom. Kant’s argument can be seen as exploiting this fact, together with the observation that there is no similar periodic process in human conscious experience considered independently of any spatial objects it might represent, and that we lack any awareness of time by itself, to show we must perceive objects outside us in space by reference to which we can determine the temporal order of our past experiences.