 In early 1666, at age 19, Leibniz wrote his first book, "De Arte Combinatoria" ("On the Combinatorial Art"), the first part of which was also his habilitation thesis in Philosophy, which he defended in March 1666.His next goal was to earn his license and Doctorate in Law, which normally required three years of study.In 1666, the University of Leipzig turned down Leibniz's doctoral application and refused to grant him a Doctorate in Law, most likely due to his relative youth.