Why Theaetetus Wonders

Many commentators struggle to explain why thauma is a fitting response to the dice and height comparisons in Plato’s Theaetetus. I argue that Socrates employs these comparisons to test the cogency of Protagoreanism and remind Theaetetus of his mathematical lesson with Theodorus. In this way I align Theaetetus’ wonder with the various senses in which Plato typically employs thaumazein and its cognates. Theaetetus is surprised that the comparisons validate Protagoreanism; he desires to know whether this implausible metaphysics can be squared with more intuitive principles; and he is ultimately led to marvel at the irrational length, an extraordinary measure.