Metaphysics has unergone a major reform in the second half of the 18th century thanks to the efforts of Johann Heinrich Lambert and Immanuel Kant. The turning point was the publication in 1764 of the 'Neues Organon' by Lambert in the printing offices of Johann Heinrich Wendler in Leipzig and the publication in 1781 of the first edition of the 'Critique of Pure Reason' by Immanuel Kant in the printing offices of Johann Heinrich Hartknoch in Riga. The span of nearly seventeen years between these two books is very significant. Kant used the time to analyse premises for the reform of metaphysics, the premises which he himself had extracted from Lambert's system. Then he devised a concept of metaphysics that was later developed into a theory presented in the first edition of the 'Critique of Pure Reason'. These 'almost seventeen years' in Kant's work have been marked by such works as 'Träume eines Geistersehers, erläutert durch Träume der Metaphysik', 'De mundi sensibilis atque intelligibilis forma et principiis', and the 'Critique of Pure Reason'. In the same period, and especially in the years 1765 through 1770, Kant conducted a lively correspondence with Lambert, and their letters can be used to sustain two main hypotheses of this paper. First, it can be demonstrated that Kant's attempt to undertake a reform of metaphysics in the pre-critical version was inspired by Lambert. Secondly, the 'Critique of Pure Reason' is the first successful attempt to venture beyond the compass of the dogmatic presuppositions imposed on metaphysics by Descartes, Leibniz and Wolff, and to found metaphysics on new, transcendental premisses.