Thomas Aquinas (1224/25-1274) can be regarded as one of the most important representatives of Latin philosophy and theology in the Middle Ages. He joined the Dominican Order at an early age, studied under Albertus Magnus in Paris and Cologne, and then taught in Paris and Italy. In the commentary presented here on Boethius's work "De Trinitate," which Thomas wrote at the beginning of his first teaching position in Paris between 1256 and 1258, he develops his theory of science, which is significant for the debate on the theory of sciences in the Middle Ages.