Sextus Empiricus, Against the Professors (Adversus mathematicos) 2.12 (Critolaus, fr. 32 Wehrli 1969b)

So just as I would not say that there is an art of burglary which instructs one that this is how one should burgle, or of thieving [which instructs one] that this is how it is appropriate to thieve and snatch purses (for these things are false, and neither appropriate nor scientific principles), just so one should not suppose that rhetoric exists as an art, tossed about on precepts like these. At any rate the followers of Critolaus the Peripatetic, and much earlier those of Plato, with this in mind abused [rhetoric] for being established as a false art rather than an art.

Quintilian, Education of the Orator 2.15.19–20, 23 ((2) = Critolaus, fr. 26 Wehrli 1969b)

(1) But those who did not regard everything as the orator’s subject matter introduced more careful and lengthy distinctions, as was necessary; among them was Ariston, the pupil of Critolaus the Peripatetic, whose conclusion is ‘the knowledge of how to identify and carry out persuasion of the public through speeches in civil disputes.’ Being a Peripatetic he does not, like the Stoics, regard this knowledge as a virtue; by including persuasion of the public he is actually rather disparaging of the art of oratory, which he does not think will persuade learned people at all . . . (2) Some people have thought that [rhetoric] is neither a power nor a science nor an art, but Critolaus [thought it] experience in speaking (for this is what tribē means), Athenaeus an art of deception.