How did St. Thomas Aquinas explain the change of bread and wine in transubstantiation?

St. Thomas Aquinas explained the doctrine of transubstantiation by utilizing Aristotelian philosophy to distinguish between the substance and the empirical appearances of the bread and wine in the Eucharist.

In his theological synthesis, Aquinas maintained that while the "accidents" (the observable characteristics such as taste, texture, and appearance) of the bread and wine remain unchanged, the underlying "substance" is miraculously transformed into the real presence of Christ—his body and blood.1

Aquinas achieved this by applying his philosophical framework, which distinguishes between essence and existence. He argued that God, as the creator, can alter the substance of a thing while allowing its accidental properties to persist, thereby safeguarding the literal truth of Christ's presence without contradicting the evidence of the senses. This Scholastic formulation became a cornerstone of Roman Catholic dogma, emphasizing that the change is not merely symbolic but a profound ontological shift.123