AbstractThis paper aims to achieve a better understanding of what Socrates means by "συμϕωνɛiν" in the sections of the Phaedo in which he uses the word, and how its use contributes both to the articulation of the hypothetical method and the proof of the soul's immortality. Section I sets out the well-known problems for the most obvious readings of the relation, while Sections II and III argue against two remedies for these problems, the first an interpretation of what the συμϕωνɛiν relation consists in, the second an interpretation of what sorts of thing the relation is meant to relate. My positive account in Section IV argues that we should take the musical connotations of the term seriously, and that Plato was thinking of a robust analogy between the way pitches form unities when related by certain intervals, and the way theoretical claims form unities when related by explanatory co-dependence. Section V surveys the work of IV from the point of view of the initial difficulties and suggests further consequences for the hypothetical method, including the logical relation between the συμϕωνɛiν and διαϕωνɛiν relations, and the need for care in ordering the results of a hypothesis."But anyhow I proceeded in this way: on each occasion hypothesising the λóγoς which I judged to be strongest, I put down as true the things that seem to me to συμϕωνɛiν with it – both about a causal account and any of the other things that are – but those things that did not I put down as false." (Phaedo 100a3-7). "But if someone clung to the hypothesis itself, you would bid him goodbye and wouldn't answer him until you had examined its results, whether according to you they συμϕωνɛi or διαϕωνɛi with one another." (Phaedo 101d3-5);
