Italian Christian philosopher and theologian whose subtle synthesis of moderate nominalism with a theology of divine grace borrowed from St. Augustine strongly influenced the mode of later medieval thought characterizing some of the Protestant Reformers.

In 1357 Gregory was elected superior general of the Augustinian monastic order after an academic career at universities in Paris, Bologna, and Padua, where opposition to his nominalist philosophy required the intervention of Pope Clement VI before he could obtain his degree and a teaching position. Becoming the leading proponent of moderate nominalism, which mitigated the more extreme skepticism of the early 14th-century philosopher William of Ockham, Gregory allowed for proofs of the existence of God and a rational demonstration of the spirituality of the soul. He assigned more importance to experience than did the Ockhamist school and, under Augustinian influence, claimed that the intellect knows the individual objects of experience by an intuitive process before it can fashion any abstract ideas. Further, he maintained that the immediate object of knowledge and science is not the object that exists outside the mind but rather the total meaning of logical propositions.

On the question of man's salvation and spiritual beatitude, Gregory taught what he conceived to be Augustinian doctrine, emphasizing the incapacity of man to lead a moral life by free will alone without divine grace. Following Augustine, he held as a transcendent principle the autonomy of God's gratuitous election of the just and their predestination to eternal glory. Sensitive to any manner of Pelagianism, a heretical doctrine that man is responsible for initiating the process of salvation by choosing a moral, and even ascetical, life independent of God's help, Gregory, to the contrary, insisted on the insufficiency of goodwill to acquire the perfect love necessary for the vision of God to which Christians aspire. He proposed, moreover, that children dying without Baptism would suffer eternal punishment, thus earning the nickname “infant torturer.” Gregory's teachings were assembled in his principal work, Lectura in librum I et II sententiarum (“Commentary on Book I and II of the Sentences,” referring to the theological synopses of the 12th-century Scholastic philosopher Peter Lombard). The widespread influence of Gregory's doctrine over much of late medieval Europe is evidenced by the similar teaching emanating from the 16th-century Augustinian faculty at the University of Wittenberg, Germany, the monastic order and the school of the Protestant Reformer Martin Luther.