preëstablished harmony which exists between all substances, as representatives of one and the same universe. Souls act according to the laws of final causes by appetitions, etc. Bodies act according to the laws of efficient causes or the laws of motion. And the two kingdoms, that of efficient causes and that of final causes, harmonize with each other." [29] [Footnote 28: In this connection, Leibnitz quotes the remarkable saying of Hippocrates, [_Greek: Sumpnoia panta_]. The universe breathes together, conspires.--_Monadal_. 61.] [Footnote 29: _Monadol_. 78, 79.] The Preëstablished Harmony, then, is to be regarded as the philosophic statement of a fact, and not as a theory concerning the cause of the fact. But, like all philosophic and adequate statements, it answers the purpose of a theory, and clears up many difficulties. It is the best solution we know of the old contradiction of free-will and fate,--individual liberty and a necessary world. This antithesis disappears in the light of the Leibnitian philosophy, which resolves freedom and necessity into different points of view and different stages of development. The principle of the Preëstablished Harmony was designed by Leibnitz to meet the difficulty, started by Des Cartes, of explaining the conformity between the perceptions of the mind and the corresponding affections of the body, since mind and matter, in his view, could have no connection with, or influence on each other. The Cartesians explained this correspondence by the theory of _occasional causes_, that is, by the intervention of the Deity, who was supposed by his arbitrary will to have decreed a certain perception or sensation in the mind to go with a certain affection of the body, with which, however, it had no real connection. "Car il" (that is, M. Bayle) "est persuadé avec les Cartésiens modernes, que les idées des qualités sensibles que Dieu donne, selon eux, à l'âme, à l'occasion des mouvemens du corps, n'ont rien qui représente ces mouvemens, ou qui leur ressemble; de sorte qu'il étoit purement arbitraire que Dieu nous donnât les idées de la chaleur, du froid, de la lumière et autres que nous expérimentons, ou qu'il nous en donnât de tout-autres à cette même occasion." [30] [Footnote 30: _Théodicée_. Partie II. 340.] If the body was exposed to the flame, there was no more reason, according to this theory, why the soul should be conscious of pain than of pleasure, except that God had so ordained. Such a supposition was shocking to our philosopher, who could tolerate no arbitrariness in God and no gap or discrepancy in nature, and who, therefore, sought to explain, by the nature of the soul itself and its kindred monads, the correspondence for which so violent an hypothesis was embraced by the Cartesians.