Bartholomew Medina, a Dominican, was the first to expound the moral system which is known as probabilism. In his Expositio in 1am 2ae S. Thomae he wrote:
|“||If an opinion is probable it is lawful to follow it, even though the opposing opinion is more probable.||”|
His system soon became the common teaching of the theologians, so that in the introduction to his Regula Morum Father Terill maintained that until 1638 Catholic theologians of all schools were probabilists. There were exceptions such as Rebellus, Comitolus and Philalethis, but the great body of the theologians around 1600 were on the side of Medina.