 There are three main sources for MM: Plato, our most important source, Aristotle, and Sextus Empiricus. All three understand the phrase—at any rate at a first level—as though “man” referred to “each individual”. In the Theaetetus MM is equated with the claim that “knowledge is sensation” and paraphrased as follows: “just as each thing appears to me, so too it is for me, and just as it appears to you, so too again for you” (Theaetetus 152a). Thus, if the wind appears warm to me, it is warm for me; and if it appears cold to another person, it is cold for her. In other words, MM means that each person is the measure of her own sensations, and Protagoras emerges as a supporter of an empiricist theory that bases knowledge on sensory data.