Why did medieval philosophers use the phrase “nothing in the intellect that was not previously in the senses”?

Medieval philosophers utilized the phrase “nothing in the intellect that was not previously in the senses” to articulate an empiricist position regarding the origin of human concepts. This perspective, which gained prominence as Aristotelian thought displaced earlier Platonic and Augustinian models, rejected the existence of innate ideas.12

Instead, philosophers like St. Thomas Aquinas argued that all human ideas are abstracted by the intellect from sensory experience. In this process, the active intellect isolates essential elements from the images received through the senses, allowing the mind to form general concepts. While these thinkers acknowledged that humans could possess nonempirical knowledge—such as understanding unseen things like God or angels—they maintained that such knowledge is derived by analogy from what is initially perceived through the senses. By grounding the formation of concepts in empirical observation, they established a framework where the mind actively processes sensory data to construct knowledge.12