The development of Melanchthon's beliefs may be seen from the history of the "Loci". In the beginning Melanchthon intended only a development of the leading ideas representing the Evangelical conception of salvation, while the later editions approach more and more the plan of a text-book of dogma. At first he uncompromisingly insisted on the necessity of every event, energetically rejected the philosophy of Aristotle, and had not fully developed his doctrine of the sacraments. In 1535 he treated for the first time the doctrine of God and that of the Trinity; rejected the doctrine of the necessity of every event and named free will as a concurring cause in conversion. The doctrine of justification received its forensic form and the necessity of good works was emphasized in the interest of moral discipline. The last editions are distinguished from the earlier ones by the prominence given to the theoretical and rational element.