The discussion with Locke was a failure:  Locke would not play, and the book in which the whole controversy was to be systematized never appeared.  The discussion with Bayle, on the other hand, was a model of what a discussion should be.  Bayle played up tirelessly, and was never embarrassingly profound; he provided just the sort of objections most useful for drawing forth illuminating expositions; he was as good as a fictitious character in a philosophical dialogue.  And the book in which the controversy was systematized duly appeared with great eclat.

Here is the history of the controversy.  In 1695 Leibniz was forty-nine years old.  He had just emerged from a period of close employment under his prince’s commands, and he thought fit to try his metaphysical principles upon the polite world and see what would come of it.  He therefore published an article in the Journal des Savants under the title:  ’New System of Nature and of the Communication of Substances, as well as of the Union between Soul and Body’.  In the same year Foucher published an article in the Journal controverting Leibniz; and in the next year Leibniz replied with an ‘Explanation’.  A second explanation in the same year appeared in Basnage’s Histoire des Ouvrages des Savants, in answer to reflexions by the editor.  M. Pierre Bayle had all these articles before him when he inserted a note on Leibniz’s doctrine in his article on ‘Rorarius’, in the first edition of his Historical and Critical Dictionary.  The point of connexion between Rorarius and Leibniz was no more than this, that both held views about the souls of beasts.

Pierre Bayle was the son of a Calvinist pastor, early converted to Catholicism, but recovered to his old faith after a short time.  He held academic employments in Switzerland and Holland; he promoted and edited the Nouvelles de la Republique des Lettres, and he produced that extraordinary work the Historical and Critical Dictionary. The notices it contains of authors and thinkers are little more than pegs upon which Bayle could hang his philosophical reflexions.  He could write an intelligent discussion on any opinion; what he could not do was to reconcile the points of view from which he felt impelled to write upon this author and that.[35] His was not a systematic mind.  So far as he had a philosophical opinion, he was a Cartesian; in theology he was an orthodox Calvinist.  He could not reconcile his theology with his Cartesianism and he did not try to.  He made a merit of the oppositions of faith to reason and reason to itself, so that he could throw himself upon a meritorious and voluntary faith.