Incommensurability and Definition in Plato's Theaetetus

Unlike most readings of Plato’s Theaetetus, which concentrate on gnoseology, this paper places it in the debate on commensurable and incommensurable magnitudes that distinguished Greek philosophical and mathematical thought at the beginning of the 4th century BC and in which Theaetetus played a leading role. The argumentation of the dialogue shows clearly how this debate was important for Plato, to the point that the entire dialogue can be considered as an attempt to consider seriously how incommensurability, and its ontological correlate, the concept of dynamis, could elaborate a new form of logos.