will give an overview of the fascinating communication between G. W. Leibniz and Pierre Bayle on pre-established harmony and sudden change in the soul which started from Bayle’s footnote H to the article “Rorarius” in his Dictionnaire historique et critique (1697) and ended in 1706 with Bayle’s death. I will compare the views presented in the communication to Leibniz’s reflections on the soul in his partly concurrent Nouveaux essais sur l’entendement humain (1704) and argue that many topics in the communication (...) with Bayle are discussed with more details in Nouveaux essais. I also argue that the communication helped Leibniz to respond to Locke’s views concerning uneasiness in An Essay Concerning Human Understanding, II, xxi. Bayle himself, however, was not able to completely understand Leibniz’s views on spontaneity as he was unaware of the contents of the Nouveaux essais, especially the systematic role of petites perceptions in Leibniz’s philosophy of mind. I will also reflect on whether the controversy could have ended in agreement if it would have continued longer. (shrink)