Descartes thinks that the true scientific order is that of reasons, in which one starts from the easiest and most evident truths and moves towards those that are more difficult and complex. Thus a unique, progressive, and irreversible order is established, where each member of the chain depends on those that precede it, and each thesis has a non-interchangeable place inside the doctrine. Leibniz, on the contrary, defends the idea that "une même vérité peut avoir beaucoup des places selon les differents rapports qu'elle peut avoir" (Nouveaux Essais, IV, XXI, § 4 ; GP V, p. 506). In order to avoid repetition, assembling the greatest quantity of truths in a minimum of volumes, Leibniz argues that the best scientific order is a systematic disposition in which each place refers to all the others, so that the connections among knowledge becomes clear. In opposition to the Cartesian model of system, in the Leibnizian model theses are based upon one another, and the order of truths is reversible. It is due to these differences concerning the conception of system that Leibniz, unlike Descartes, can pretend to take the best of each philosophical system in order to constitute his own, given that for him there is a certain malleability in the construction of a philosophical system.
order of reasons; systematic order; reversibility; conciliation of philosophies