I am getting together this week to visit with a sharp young philosopher. He suggested to me the essay by Alvin Plantinga, "How To Be an Anti-Realist." Towards the end of the essay Plantinga turns toward Augustine and Thomas as providing a way to think about realism.
The quote from Thomas Aquinas is wonderful:
"Even if there were no human intellects, there could be truths because of their relation to the divine intellect. But if, per impossible, there were no intellects at all, but things continued to exist, then there would be no such reality as truth." (De Veritate !. 1, A.6 Respondeo).
Plantinga then writes: "The thesis, then, is that truth cannot be independent of noetic activity of the part of persons. The antithesis is that it must be independent of our noetic activity. And the synthesis is that truth is independent of our intellectual activity but not of God's" (p. 68 of Plantinga's essay).