 Premise (1) is intended as a claim the skeptic about the legitimate applicability of a priori concepts will at least initially accept. The crucial necessary conditions, expressed by (3) and (7), are necessary conditions of only possible explanation. However, Paul Guyer forcefully argues that establishing the need for synthesis by means of a priori concepts would require ruling out the alternative explanation that empirical information and concepts derived from it is sufficient to account for the recognition of the unity at issue (Guyer 1987:146–7). And in his view it remains open, given what Kant has shown, that this recognition requires only awareness of information derived from inner sense or introspective experience. Kant does not attempt at this point in the argument to rule out such a rival empiricist hypothesis, but he arguably would need to do so to establish the need for a priori synthesis. To advance his claims, one might appeal to features of this unity that would render such an empiricist account inadequate. As we shall see, Kant employs this tactic in the next phase of the argument, which introduces his account of our representations of objects.