Note 25 — Book I. Grammatica

Illustratio is Quintilian’s word (and Cicero’s, he says) in VI. ii. 32, where he is exhibiting the same sort of development as is here indicated by John. For historia, argumentum, fabula see the index. That these were elementary school exercises suggests that the subject of this sentence (Illi) refers not to authors, but to schoolboys engaged in developing a materia; but the reference can hardly be determined in PL, in which the whole sentence seems to me dubious.