Abstract
In this essay Socrates' 'second voyage' ('deuteros pious') in the problem of causality (Phaedo 99 D) is called a philosophical conversion. This conversion is not the beginning of Socrates' live as a philosopher, but an important biographical fact in a philosopher's live and a beginning of a second live, here told by Socrates himself in a discussion about the pretentions of philosophy. Nor is the conversion of Socrates simply, as Cicero said, a change of interest and a switch from cosmic subject to human and social questions, but chiefly the consequence of a disappointment in the philosophy of nature as practised by Socrates before and by Anaxagoras. In Plato's Phaedo this disappointment is ascribed to the fact that in the philosophy of nature a causal explanation always seems to mean a reduction from one thing to another e.g. from thought to air. The second voyage, proposed by Socrates as a primitive way of thinking and almost as a tautology, is inspired by his interest for the thing as it is in it self. Not the object of knowledge is changing in this conversion, but the method and the reflexion about philosophy. Socrates demonstrates this change in a brief exposition of the 'doctrine' of ideas and of participation. In the context of Plato's Phaedo the idea is primarily the irreductible identity of the concrete thing