Protagoras · Philosophy
Protagoras opened his book <em>Truth</em> with the most famous sentence of the sophistic age: ‘Man is the measure of all things - of the things that are, that they are; of the things that are not, that they are not.’ With it he made human experience, rather than an independent reality, the standard of what is true.
Around the middle of the fifth century BC, in the brilliant and turbulent Athens of Pericles, a travelling teacher from the northern city of Abdera became the most celebrated intellectual of his age. Protagoras was the first and greatest of the sophists - professional teachers of wisdom and excellence who, for a fee, trained ambitious young men in the arts of argument, persuasion, and public life. He was famous, wealthy, and respected; Plato portrays the young men of Athens flocking to hear him. And he opened his book, titled Truth, with a single sentence that would echo for two and a half thousand years: ‘Of all things the measure is man: of the things that are, that they are; of the things that are not, that they are not.’
This sentence - the homo mensura or ‘man-measure’ doctrine - is one of the boldest claims in the history of thought, and it inaugurated a debate that has never ended. A ‘measure’ is a standard, a yardstick, the thing by which we judge whether something is so. Protagoras’ claim is that the standard of what is true, of what is and is not, is man - the human perceiver and judge. Not the gods, not an eternal reality, not the nature of things in themselves, but human experience is the measure of truth. Whatever appears to a person to be the case is the case, for that person. With this single stroke Protagoras moved the criterion of truth from the world to the knower - and raised, for the first time with full clarity, the dizzying possibility that there is no single, absolute truth standing over all of us, but only truth-for-each.
Protagoras’ doctrine is easiest to grasp through the kinds of example he and his interpreters used, drawn first from sense-perception. Consider the honey that tastes sweet to a healthy person and bitter to someone who is ill, or the breeze that is pleasantly cool to one and bitingly cold to another, or the food that is wholesome for one constitution and sickening for another. In each case the same thing produces opposite appearances in different perceivers. The ordinary assumption is that one appearance is correct and the other a misperception - the honey is really sweet, and the sick person’s palate is malfunctioning. Protagoras rejects this assumption. Each perception is true for its perceiver: the honey is sweet-for-the-healthy and is bitter-for-the-sick, and there is no neutral, perceiver-independent fact about its ‘real’ taste that would make one of them simply wrong.
The genius - and the danger - of the doctrine is that it does not stop at taste and temperature. Protagoras extended ‘man is the measure of all things,’ and his ancient interpreters took this to cover not only sensible qualities but values and even, on some readings, every kind of claim. If beauty, justice, and goodness are also ‘measured’ by the perceiver, then what is just is just for the society or person that holds it just, and what is beautiful is beautiful for the one who finds it so, with no culture-transcending standard to adjudicate. Things become true in relation to a measurer, the way ‘to the left’ is true only in relation to a position. This relational character is the heart of the matter: for Protagoras, truth is never simply ‘true,’ full stop, but always ‘true for’ some perceiver or community - and the moment you remove the perceiver, the truth, like the leftward direction without a vantage point, has nothing left to attach to.
Protagoras’ ‘man is the measure’ is the fountainhead of relativism - the family of views holding that truth, knowledge, or value is not absolute but relative to a perceiver, a culture, a framework, or a point of view. Nearly every later relativism, down to our own age of ‘your truth’ and ‘my truth,’ is in some sense a descendant of this single Greek sentence. And the questions it raises are not antiquarian curiosities but live and pressing concerns. Is there an objective truth about the way the world is, independent of how it seems to us - or is all truth, in the end, truth-for-someone? When cultures disagree about justice or morality, is one of them right and the other wrong, or are both merely ‘true for them’? Can we ever step outside our own perspective to grasp things ‘as they really are,’ or are we forever locked within the measure of our own experience? Protagoras put all of these on the table for the first time.
The doctrine matters, too, because of the storm it provoked - for the deepest critiques of relativism were developed precisely in response to it. Plato’s sustained refutation in the Theaetetus, and the objections that grew from it, constitute the classic case against relativism, and they remain the arguments any relativist must answer. So Protagoras is doubly important: he is the founder of relativism, and he is the provocation that forced its opposite into being. To engage his doctrine is to engage one of the permanent fault-lines of philosophy - between those who hold that there is a single truth measuring us all, and those who hold that we are, each of us and each of our communities, the measure of our own. Few sentences in the history of thought have done so much work, or stirred so much trouble, as the one with which Protagoras opened his book.
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 declared ‘man is the measure of all things - of the things that are, that they are; of the things that are not, that they are not.’ This makes the human perceiver, not an independent reality, the standard of truth: things are for each person as they appear to that person. The wind that feel…
Leads to Plato.
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