Few have defined what free will is, although it repeatedly occurs in the writings of all. Origen seems to have put forward a definition generally agreed upon among ecclesiastical writers when he said that it is a faculty of the reason to distinguish between good and evil, a faculty of the will to choose one or the other. Augustine does not disagree with this when he teaches that it is a faculty of the reason and the will to choose good with the assistance of grace; evil, when grace is absent.

…John Calvin (1509-1564), The Institutes of the Christian Religion, ii.2.4 [1559]