In 1791 Karl Leonhard Reinhold expressed full agreement with Kant’s verdict that appeal to common understanding is not acceptable in philosophy. Only three years later Reinhold presented a philosophical methodology in which common understanding was explicitly assigned an essential function. In my contribution, I shall first reconstruct Reinhold’s account of the relation between common understanding and philosophising reason (Section 2). According to this account, common understanding is supposed to provide a multitude of empirical facts of consciousness. Philosophising reason takes these facts as the starting point of philosophical analysis and establishes their a priori, transcendental grounds. Common understanding and philosophising reason thus fulfil complementary roles: philosophy analyses, explains, and justifies the basic beliefs of common understanding; philosophical claims are, in turn, substantiated through their reference to the facts provided by common understanding. I shall also show that the account of the relation between common understanding and philosophising reason enables Reinhold to deal with some objections against his philosophical system. The appeal to common understanding thus serves the purpose of corroborating the structure and the contents of the Elementarphilosophie. In Section 3, I shall suggest that Reinhold’s introduction of common understanding was not influenced by common-sense philosophy but rather by the Wolffian conception of the relation between common cognition and philosophical cognition. Reinhold accepted the general outline of Wolff’s rationalist conception but adopted it to the framework of critical philosophy. In my concluding remarks (Section 4) I shall briefly indicate that the main characteristics of the account of the relation between common understanding and philosophical reason withstood Reinhold’s later changes of philosophical systems.