Protagoras · Philosophy
Protagoras’ relativism rests on a picture of a world in flux, perceived by perceivers who are themselves changing, so that perception is always an interaction yielding truth-for-each. Plato linked this to Heraclitus’ doctrine that all things flow - and argued that on such a view, no stable truth, not even Protagoras’ own, can be stated.
Why should anyone believe that man is the measure of all things - that truth is truth-for-each rather than one and the same for all? Protagoras did not assert it as a bare slogan; the doctrine rests, at least as Plato reconstructs it, on a picture of how the world and our perception of it actually work. The picture is this: the world is not a collection of fixed, stable things with settled properties waiting to be correctly perceived. It is a ceaseless flow, a process of constant change, in which nothing simply is anything but everything is always becoming. And the perceiver, too, is part of this flow - our bodies and senses are themselves continually changing, never twice in exactly the same state. Perception, then, is not a snapshot of a static object by a static eye; it is a fleeting encounter between a changing perceiver and a changing world, and what is perceived - the warmth, the sweetness, the colour - comes into being only in that encounter, and only for that perceiver, at that moment.
On this view, relativism is not an arbitrary doctrine but the natural consequence of a deep truth about reality: that it flows. If the wind that meets my changing body at this moment produces in our encounter the quality ‘cold-for-me-now,’ and the same wind meeting your different body produces ‘warm-for-you-now,’ then there is no ‘the wind in itself’ that is simply cold or simply warm - there is only the stream of encounters, each yielding its own truth-for-a-perceiver. The man-measure doctrine, in other words, is the epistemology that fits a metaphysics of flux. To understand why Protagoras held it, we must understand the flowing world he (or his interpreters) saw beneath it - and that world has a famous author: Heraclitus, the philosopher of universal change.
Plato develops the flux-based theory of perception with great care in the Theaetetus, presenting it as the ‘secret doctrine’ underlying Protagoras’ slogan, and the mechanism repays attention. Nothing, on this theory, has a quality ‘in itself’; qualities arise only from the interaction of two factors, an active and a passive, which meet and generate a pair of ‘offspring.’ When the eye (the active or passive partner) meets a suitable object, the meeting generates two things at once: a perceiving - the seeing - on the side of the eye, and a perceived quality - the whiteness, say - on the side of the object. Neither the seeing nor the whiteness existed before the encounter; both are born of it, together, and both perish when the encounter ends. The whiteness is not a property the object had all along, sitting there to be detected; it is something that comes to be only in the meeting of this object with this perceiver, and is therefore strictly relative to that meeting.
This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.
You learned that Protagoras’ relativism was linked (by Plato) to the Heraclitean doctrine that all things are in flux: since both the perceived object and the perceiving subject are constantly changing, perception is an interaction between them, and what is perceived exists only in that fleeting meeting - true for tha…
Leads to Heraclitus.
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