This argument (typically called the “affinity argument”) is central to the structure of the Phaedo, setting up much of the remainder of the dialogue. Moreover, it develops the dialogue’s most detailed account of the forms and of ordinary objects, and it argues for an innovative account of the nature of the soul, which is relied upon in Socrates’ ethical account in the next section. Despite this, the argument has received very little scholarly attention, supposedly because scholars widely view it as an especially bad argument. This chapter shows that the argument is much more precise and stronger than has been appreciated. In doing so, it argues that Socrates describes here a new, fundamental feature of the forms: they are simple in a way that makes them partless – in strong contrast to ordinary objects, whose complex structure allows them to have opposing features at the same time.

Socrates argues here that the sole pursuit of philosophers is dying and being dead. In doing so, he introduces most of the key topics in the dialogue, including forms, inquiry, the soul, and the philosophical life. Nonetheless, this section of the dialogue is often overlooked, perhaps because it seems simply to assert many of its claims. I argue that we often must wait until later in the dialogue to find the explanation for these claims, as part of the Phaedo’s unfolding structure. Once we take this section seriously, we can appreciate its tight and careful argumentative structure. Moreover, Socrates’ accounts here, in particular his ethical account, are sophisticated theories in their own right. The section also introduces some unusual and important terminology that Socrates uses later in the dialogue, including “auto kath’ auto” (which I argue should be translated “itself through itself”) and terminology for identifying the forms. The chapter ends with a new account of the famous “exchange passage.”