What the OP is referring to is the philosophical position on universals. Thomism takes the position that they are real. Specifically, he’s looking for Thomist critiques of conceptualist/idealist schools of thought, which hold that universals aren’t real in the world but are “ideals” in the mind which we apply to our perceptions.
I don’t have a particular source in mind, but the critiques I’ve seen focus on the weaknesses inherent to such idealism. The idealists stake their claims on not knowing anything beyond the sensible, but, regardless of their statements otherwise, they do take on faith that the ideals in the mind do bridge to the real world. There’s also objections that can be made based on common language, or even in different languages that humans can communicate at all, which again, idealism just takes for granted that we all have the same ideals.
I’ve been super brief, I know. But those are the general tacts I’ve seen. I’ve had a proponent of German idealism insist there’s no disconnect and that’s a misreading and he had me on my toes for awhile, but even the source he pointed me to for further info was heavily skeptical of transcendental idealism, and after further consideration of that and more I really don’t feel he’s justified his position as being any simpler or more plausible than realism.
