Mendelssohn and Kant:: a singular alliance in the name of reason

Metaphysics is a field where the positions of Kant and Mendelssohn differed significantly, from the essays for the Academy of Sciences right up to their last works. While Kant is increasingly doubtful of the objective validity of metaphysics and comes to admit only its subjective significance as a reflection of insuppressible human need, Mendelssohn continues to defend its objective validity with respect to sciences and natural theology. After reducing the valid proofs for the existence of God to the ontological argument, Kant refuses this argument by means of his conception of existence as a position. Meanwhile, Mendelssohn upholds the legitimacy of such an argument and sees it as a bulwark against scepticism and Kant's paradox of the thing-in-itself. Notwithstanding these differences, they are allies in the defence of reason against visionary exaltation, as becomes apparent in the debate on spinozism between Hamann, Jacobi and Wizenmann on the one hand; and Mendelssohn on the other. The profound and pertinent dialogue between the two philosophers lasted more than 20 years and touched upon many subjects; such as the different methods in mathematics and philosophy, the philosophical meaning of intensive magnitude, the evidence, certainty and probability in metaphysics, natural theology and morals, reason, feeling and moral sense, pure religion and historical faiths, the meaning of human history. They agreed on attributing a fundamental role to freedom and on evaluating religions accordingly. Kant acknowledged the importance of M's Jerusalem for human emancipation. However; he criticised Judaism as a religion for slaves in Religion within the Boundaries of Mere Reason and so misunderstood M's affection for his own faith. They were also at variance over the progress of the human race; while Kant subscribed to the optimistic point of view and linked the efforts for human betterment to confidence in the progressive improvement of the human race even in the moral sphere, Mendelssohn rejected this evolutionary scheme and insisted upon the originality and diversity of human beings in different civilisations and times. Their differences were far from being resolved and the interest in Mendelssohn's thought during the Idealist period and later gives clear evidence of that