How did Aquinas contribute to the concept of realism?

Aquinas contributed to the concept of realism primarily through his arguments for moderate realism. This philosophical position asserts that universals, or general concepts, exist in a way that is neither entirely abstract nor purely concrete. In Aquinas's view, universals are grounded in particular objects; they have a basis in reality but do not exist as separate, independent entities.

By advocating for moderate realism, Aquinas sought to reconcile faith and reason, asserting that knowledge gained through sensory experience can lead to understanding universal truths. This perspective marked a significant development in the philosophy of the time, influencing subsequent thought in both philosophy and psychology. His approach allowed for a more nuanced understanding of the relationship between the mind and the world, as well as the nature of existence itself, distinguishing his thoughts from more radical philosophical positions that either deny the independent existence of universals or embrace extreme subjective interpretations of reality.