Though the universities held to accepted philosophy and theology, some of them became centers of progressive thought. Out of the universities came all the great reformers and progressive leaders including John Wycliffe at Oxford, Martin Luther at Wittenberg, John Calvin at Geneva, and John and Charles Wesley at Oxford.
Clergy who became Schoolmen were suspected by the Church of heresy, yet they were only trying to understand the Christian teachings that had been handed down from the ancient Church and to justify it by their reason. Even Thomas Aquinas did not escape the charge of introducing dangerous doctrines, though he became the accepted master of Catholic theology. They did not intend to overstep the bounds of authority, but they mark the beginning of the modern tendency toward critical thought directed toward even the most sacred themes of the Christian tradition.