The syncretistic controversy was the theological debate provoked by the efforts of Georg Calixt and his supporters to secure a basis on which the Lutherans could make overtures to the Roman Catholic and the Reformed Churches. It lasted from 1640 to 1686.
Calixt, a professor at Helmstedt, had through his travels in England, the Netherlands, Italy, and France, through his acquaintance with the different Churches and their representatives, and through his extensive study, developed a more friendly attitude towards the different religious bodies than the majority of his contemporary Lutheran theologians.
While the latter firmly adhered to the "pure doctrine," Calixt tended not to regard doctrine as the one thing necessary for a Christian; while in doctrine itself he did not regard everything as equally certain and important. Consequently, he advocated unity between those who agreed on the fundamental minimum, with liberty as to all less fundamental points. In regard to Catholicism, he would have (as Melanchthon once would have) conceded to the pope a primacy human in origin, and he also admitted that one might call the Mass a sacrifice.
On the side of Calixt stood the theological faculties of Helmstedt, Rinteln, and Königsberg; opposed to him stood those of Leipzig, Jena, Strasburg, Giessen, Marburg, and Greifswald. Abraham Calov in especial opposed Calixt.