Malcolm WILSON Is Plato's Republic VI the Target of Aristotle's Posterior Analytics I.32

Aristotle argues at Posterior Analytics I.32 that one cannot demonstrate all syllogisms from a single set of principles. It has been common to treat this chapter as an attack on Plato's universal Form of the Good (Rep. 511b). A careful reading of both passages, however, reveals that Plato is not advocating a universal science in the Aristotelian mode nor is Aristotle criticizing Plato. Aristotle is, instead, continuing the attack against sophistic deduction that he initiated in APo I.5. Evidence from the Sophistical Refutations shows that he accused the sophists of arguing all things from general principles and with failing to draw generic distinctions.

A superficial reading of Republic VI (511b) suggests that the idea of the Good is the single scientific principle from which alone all knowledge of Forms and the mathematical sciences can be demonstrated, or as Aristotle puts it, that there are the same principles for all syllogisms. A closer reading reveals that Plato did not mean anything so Aristotelian. In the APo Aristotle is unambiguous in attacking the universal science, the view that all knowledge forms a unified whole. Plato, by contrast, advocates the master science, which rectifies the principles of mathematics and other sciences without actually taking them over. In APo I.32 Aristotle is offering a refutation of the universal science, and has no interest in Plato's master science.

It is in the early chapters of APo I that we may best look for a target for the arguments of I.32. We find there that the notion of the autonomous genus arises from the need of demonstration for necessary predication. A syllogism whose premisses are not necessary is not a demonstration, since it proves only an incidental connection, one that strays from the genus at hand. Such syllogisms prove only in a sophistical way (I.5 74a28-9). A parallel passage in SE 6 (168a40-b4) makes clear that this sofistiko;" trovpo" refers to the error called incidental reasoning. The sophistic target is further confirmed by arguments in I.32, which are utterly inappropriate for a Platonic target (88a18-30). Here Aristotle takes the side of Plato in attacking the sophist and the practice of ajntilogikhv based on incidental reasoning. This chapter makes clear, then, the association of sophistry with arguments which are both non-deductive and which are derived from common or universal principles: the sophist makes no distinction among genera. Far from attacking Plato, then, Aristotle is taking up the common cause against the sophist.