Auctor ad Herennium 
He has been identified with the author of the four books of Rhetorica dedicated to a certain Gaius Herennius (otherwise unknown). The work is generally known under the title of Auctor ad Herennium, or Rhetorica ad Herennium . The chief argument in favor of this identity is the fact that many passages quoted by Quintilian from Cornificius are reproduced in the Rhetorica. Jerome, Priscian and others attributed the work to Cicero (whose De inventione was called Rhetorica prima, the Auctor ad Herennium, Rhetorica secunda), while the claims of L. Aelius Stilo, M. Antonius Gnipho, and Ateius Praetextatus to the authorship have been supported by modern scholars.
Internal indications point to the date of compositions as 86 BC-82 BC/ the period of Marian domination in Rome. The unknown author, as may be inferred from the treatise itself, did not write to make money, but to oblige his relative and friend Herennius, for whose instruction he promises to supply other works on grammar, military matters and political administration. He expresses his contempt for the ordinary school rhetorician, the hair-splitting dialecticians and their sense of inability to speak, since they dare not even pronounce their own name for fear of expressing themselves ambiguously. Finally, he admits that rhetoric is not the highest accomplishment, and that philosophy is far more deserving of attention. Politically, it is evident that he was a staunch supporter of the popular party.
The first and second books of the Rhetorica treat of inventio and forensic rhetoric; the third, of dispositio, pronuntiatio, memoria, deliberative and demonstrative rhetoric; the fourth, of elocutio. The chief aims of the author are conciseness and clearness (breviter et dilucide scribere). In accordance with this, he ignores all rhetorical subtleties, the useless and irrelevant matter introduced by the Greeks to make the art appear more difficult of acquisition; where possible, he uses Roman terminology for technical terms, and supplies his own examples of the various rhetorical figures. The work as a whole is considered very valuable.
Cicero's De inventione 
The question of the relation of Cicero's De inventione to the Rhetorica has been much discussed. Three views were held: that the Auctor copied from Cicero; that they were independent of each other, parallelisms being due to their having been taught by the same rhetorician at Rome; and that Cicero made extracts from the Rhetorica, as well as from other authorities, in his usual eclectic fashion. One of the 19th century editors, Friedrich Marx, puts forward the theory that Cicero and the Auctor have not produced original works, but have merely given the substance of two technai (both emanating from the Rhodian school); that neither used them directly, but reproduced the revised version of the rhetoricians whose school they attended, the introductions alone being their own work; and that the lectures on which the Ciceronian treatise was based were delivered before the lectures attended by the Auctor.
A monument in Rome to Cornificius' sister Cornificia (also a poet) reads - CORNIFICIA Q. F. CAMERI Q. CORNIFICIUS Q. F. FRATER PR. AUGUR (Cornificia, the daughter of Quintus, wife of Camerius, her brother Quintus Cornificius, Praetor and Augur).