Dichotomy and Platonic Diairesis

by Lee Franklin

There is a puzzling discordance between the aims of Platonic diairesis and the way Plato instructs that it be performed. Our goal in the method is to provide an account or definition of a kind, based in a hierarchical taxonomy of related kinds. To succeed in this, our taxonomy must carve nature at its joints or delineate natural kinds (Phaedrus 265e1–2, Sophist 253d1–3, Statesman 262b7–c1, 287c1–2). But while Plato allows that genera may be divided into more than two species, dichotomous division is given priority throughout his presentation of diairesis. The introduction of the method in the Phaedrus indicates a preference for dichotomy (Phaedrus 265e1­66b1), and the lengthy displays of diairesis in the Sophist and Statesman are dichotomous in all but one passage (Statesman 287b10ff.). Even where he acknowledges its necessity, Plato nevertheless presents division into more than two kinds as an option for when dichotomy is impeded (Statesman 287b10–c5, Philebus 1610–d7). Why does Plato privilege dichotomy if it fails in some, and perhaps many cases, to limn the structure of nature? Noting this problem, some commentators dismiss Platonic diairesis as a method lacking genuine philosophical value; others dismiss dichotomy as an unimportant feature of the method. Those who acknowledge the significance of both diairesis and dichotomy tend to relegate the latter to an application of the method restricted in either scope or power. Currently, there is no account on which dichotomous division contributes directly to the central aim of diairesis—division by kinds—so as to warrant the priority Plato gives it. In this paper, I offer such an account.