Protagoras of Abdera
"Man is the measure of all things" — the homo-mensura doctrine as the first explicit philosophical relativism
Protagoras of Abdera was the most prominent of the fifth-century Sophists, traveling from city to city teaching rhetoric, politics, and what we would call practical philosophy, for substantial fees. His "Truth" (Aletheia, lost) opened with the homo-mensura doctrine — "Of all things the measure is man" — and was the principal classical statement of relativism. He served as lawgiver for the Athenian colony of Thurii (444 BCE) and was a friend of Pericles. Plato made him the interlocutor of the dialogue "Protagoras" and the principal target of "Theaetetus." Although later tradition reports his books were publicly burned in Athens, the historical evidence is weak; what is certain is that his doctrines survived in the Sophistic tradition that Plato spent his career rebutting.
Key works
- Truth (Aletheia, also called "On Being", lost)
- On the Gods (lost; opening sentence preserved by Diogenes Laertius)
- Antilogies (Contradictory Arguments, lost)
- (testimonia in Plato's Protagoras, Theaetetus, and Cratylus; Diogenes Laertius IX; Sextus Empiricus)
Declared Influences
Relativism 40%
Constructivism 20%
Pragmatism 15%
Pyrrhonism 15%
Platonism (Classical) -20%
Protagoras is the founder of explicit philosophical relativism; "man is the measure of all things" is the first European formulation of the position that has been the central reference point ever since.
"Man is the measure of all things — of things that are, that they are, and of things that are not, that they are not." (homo-mensura doctrine, opening of Truth, transmitted by Plato, Theaetetus 152a)
Protagoras's position that truth is relative to the perceiving subject is the proto-form of constructivism; what counts as real is constituted by the cognitive engagement.
"The wind, which feels cold to one person, does not feel cold to another. Should we say that the wind is in itself cold or not?" (Plato, Theaetetus 152b)
Protagoras's emphasis on what works in human practice over abstract metaphysical truth places him in the deep history of proto-pragmatist positions; James and Schiller (the British pragmatist) treated him as ancestor.
"A wise man is one who makes good and useful what before seemed bad and harmful." (Plato, Theaetetus 167a, in Protagoras's voice)
Protagoras's relativism is one of the principal sources for the later Pyrrhonist suspension of judgment; Sextus Empiricus treats him as ancestor.
"There are two opposed arguments concerning every thing." (Antilogies, fragment)
Plato's entire philosophical project can be read as a sustained rebuttal of Protagorean relativism — the Theaetetus most directly, but the Republic, Sophist, and Cratylus all engage the same target.
"If knowledge is perception and what each person perceives is what is, no one is wiser than anyone else." (Plato, Theaetetus 161c, the absurd consequence Plato extracts)
Internal Tensions
Protagoras is known almost entirely through Plato, who was committed to refuting him; the homo-mensura doctrine's precise scope (all judgments? only perceptual?) has been debated for 2,500 years. The self-refutation argument (if all truth is relative, the homo-mensura doctrine is itself only relatively true) is the standard objection Plato deploys; Protagorean replies (the doctrine is more useful or persuasive in some life-projects than in others) survive in proto-pragmatist form.
I. Time
Relational temporality of the perceiving subject; no absolute time.
Attributes
II. Space
Relational space of human practice.
Attributes
III. Matter
Standard substantival matter, with appearances relative to perceivers.
Attributes
IV. Observer
Plural perceiving subjects, each the measure of their own world. No metaphysical agency ("Concerning the gods I cannot know whether they exist or what they are like" — On the Gods, fragment).
Attributes
V. Energy
Standard physics (within fifth-century BCE intellectual scope).
Attributes
VI. Information
Information relative to perceivers; no personal soul-doctrine.
Attributes
Classified works
Works in the atlas that Protagoras of Abdera authored or that draw on this persona's writings, with full attribute fingerprints of their own.
Computed school proximity
The persona's attribute fingerprint scored against all 202 schools using the same quiz scorer. Useful as a sanity check on the hand-curated influences above.
Philosophical neighbors
Other personas whose attribute fingerprint sits closest to Protagoras of Abdera's — intellectual neighbors across traditions and eras.
How Protagoras of Abdera resolves each dilemma
56 resolved positions across 4 dimensions, including 4 distinctive where the majority of schools go the other way · 1 unaligned.
Each dimension is sorted so minority positions come first. Mainstream positions are folded into an expandable list.
Time · 9 dilemmas · 3 distinctive
Persistence, the future, and the direction of becoming.
6 mainstream positions
Matter · 7 dilemmas, all mainstream
Observer · 37 dilemmas · 1 distinctive
Mind, agency, and the knower's relation to the known.
35 mainstream positions
Information · 4 dilemmas, all mainstream
Appears in Debates (1)
Films Referencing This Persona (2)
Either directly referenced in the film, or reading the film through one of this persona's top schools.
Experiments Engaging This Persona's Schools
Surface via influence-schools that respond to the experiment. Each entry shows the school through which the connection runs.