The recognition of unity may have features that empirical information and introspective experience alone cannot account for

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