In Quintilian's time, rhetoric was primarily composed of three aspects: the theoretical, the educational, and the practical. "Institutio Oratoria" does not claim originality; Quintilian drew from a number of sources in compiling his work. This eclecticism also prevented him from adhering too rigidly to any particular school of thought on the matter, although Cicero stands out among the other sources. Quintilian also refused any short, simple lists of rules; he evidently felt that the study and art of rhetoric could not be so reduced. This might explain the length of "Institutio Oratoria", which consists of twelve books.