What philosophical concept did St. Thomas Aquinas elaborate that pertained to the doctrine of transubstantiation?

St. Thomas Aquinas advocated for Thomism, a philosophical framework that he developed which integrated Aristotelian philosophy with Christian theology. This school of thought played a crucial role in articulating the doctrine of transubstantiation, which holds that during the Eucharist, the substance of bread and wine is transformed into the actual body and blood of Christ while retaining their accidents, or superficial properties.

Thomism is foundational in understanding how Aquinas reconciled faith and reason, using rational arguments to explain and defend the mysteries of faith, including transubstantiation. Through his works, particularly in the "Summa Theologica," Aquinas provided a detailed exposition of how the presence of Christ in the Eucharist could be understood philosophically and theologically, affirming that the bread and wine, although unchanged in appearance, were indeed transformed in their substance.

This integration of philosophy and theology in Aquinas's thought is significant, as it provided a systematic approach to understanding important theological concepts like transubstantiation within the framework of reason, influencing Catholic doctrine for centuries to come.