 He wrote only two book-length philosophical treatises, of which only the "Théodicée" of 1710 was published in his lifetime.Leibniz dated his beginning as a philosopher to his "Discourse on Metaphysics", which he composed in 1686 as a commentary on a running dispute between Nicolas Malebranche and Antoine Arnauld.This led to an extensive and valuable correspondence with Arnauld; it and the "Discourse" were not published until the 19th century.