Historian: Because medieval epistemology (theory of knowledge) is a complex subject, intellectual historians have, until recently, failed to produce a definition that would help to determine what should and what should not be included in it.
Conclusion
The solution for defining which things were believed by medieval epistemologists is to say it's "the epistemological beliefs of the medieval epistemologists".
Evidence
If any medieval epistemologists believed claim X, then we'll say "medieval epistemology believed X".
If any medieval epistemologists believed claim X was false, then we'll say "medieval epistemology did not believe X".
Evaluate
Won't this method lead to a bunch of contradictions, assuming that different medieval epistemologists probably believed different things.
If the 10 of them believed X was true and 10 of them believed the opposite were true, then following this author's plan we would say that "medieval epistemology both believed and didn't believe X".
Goal
Look for something pointing out this potential for self-contradictory statements about what medieval epistemology believed.
Or challenge the author's assumption that medieval epistemologists would have had unanimous consensus on beliefs, since that is the only way his plan would actually work.