The preferred approach of commentators to both these tasks has been to find symmetrical structure and categorical significance by pairing the eight hypotheses, and to justify their reading of the categorical surplus in term of their accurate account of the symmetrical structure. The argumentative structure is not the primary guide for interpreting the Parmenides . A person with any two of these faults can improve. Taking tragic heroes to be people with only one of these three faults, people with virtuous habits and right beliefs who will not listen to reason, would solve a longstanding interpretive problem in Aristotle's Poetics . The vicious tragic heroes can deliberate, but will not listen to reason.
Natural slaves have a complimentary deficiency.
By limiting slavery to natural slaves and stipulating that natural slaves must be better off enslaved than free, Aristotle severely criticizes the prevalent, exploitive practice of slavery of his day, and proposes to transform it into a new, benign institution for caring for the mentally ill. Aristotelian slavery is an infelicitously named, for-profit halfway house providing a structured environment for the dysfunctional. The rest of the incurably mentally ill are the brutish. When in chapter eleven of Metaphysics Z Aristotle questions the comparison Socrates the Younger draws between animal and circle, the text has Aristotle say that animal and circle are incomparable because an animal is something 'perceptible', aisth ton . Aristotle is critical of the comparison because it gives the false impression that the natural kind man could, like the circle, exist in different sorts of materials.