 Plato’s testimony is crucial and his reconstruction is also taken up by other authors (see 80A16 DK and 80B1 DK). It is, however, a reductive interpretation that potentially misleads. The underlying aim of Theaetetus is not to accurately report the theses of Plato’s opponent, but to show their philosophical limits: according to Plato, the MM thesis is a muddled one; the only way to make it clear is by assuming that Protagoras was only speaking of sensations; and since (according to Plato) it is impossible to base knowledge on sensations alone, it follows that the thesis is fallacious. This strict empiricist reading is philosophically interesting but not historically reliable, because Protagoras was not speaking of sensations alone. Remarkably, Plato himself suggests that Protagoras’ phrase had a broader meaning by remarking that MM also concerned all opinions and judgements (157d, 170a–171a). Aristotle and Sextus Empiricus further confirm the need for a broader interpretation: what are at play are not just sensations but more generally all opinions and judgements (and especially value judgements). On this interpretation, MM means that each individual is the ultimate arbiter of all her own judgements—not only that the wind is warm or cold, but also that performing a given action is right or  wrong.[1]