Abstract: Diogenes Laertius tells us that Protagoras was the first to use ‘the Socratic form of argument’. I argue that we have good reason to think this is true. Plato’s Protagoras shows Protagoras deploying what was plausibly the original form of the Socratic elenchus, and that this was characteristic is confirmed by other evidence. This original ‘double-decker’ (or ‘literary’) form of the elenchus was, if we trust Plato’s own evidence, a vehicle for serious discussion of ethical questions, useful as a method both of teaching and of philosophical inquiry.  Socrates’ only innovation was to eliminate its reliance on a text.