Q0181
“Of all things the measure is man.” — Protagoras (DK 80B1 (via Plato, Theaetetus))
Verified English quotation. Primary source: DK 80B1 (via Plato, Theaetetus). Theme: knowledge.
English
Of all things the measure is man.
Source and attribution
The archive attributes this English wording to DK 80B1 (via Plato, Theaetetus) and files it under Sophists. That locator distinguishes the passage from loose internet attributions: readers can return to the named work or section to check translation, surrounding argument, and edition-specific wording.
About Protagoras
Protagoras (c. 490–c.
Interpretation
Protagoras's measure doctrine is usually read as relativism, and Plato's Theaetetus — our source — pushes it that way. The Greek is ambiguous: "of all things" may mean things are as they appear to each person, or that a human being is the standard for judging them. Either reading made the claim famous and contested, since it appears to remove any court of appeal above individual appearance.
Why it matters
The difficulty it raises is still live: if disagreement is settled by whose appearance counts, there is no disagreement to settle — which suggests the doctrine cannot be stated coherently.
Concepts in this quote
- Knowledge
- Knowledge is the philosophical study of what we can justifiably claim to know—and where certainty ends.
- Humanity
- Humanity names both the species and the moral quality of being humane—bridging anthropology and ethics.
How to cite this quotation
APA: Protagoras. (n.d.). Of all things the measure is man. In Philosophy Blind Box. https://www.philosophydef.com/quotes/q0181
MLA: Protagoras. “Of all things the measure is man..” Philosophy Blind Box, https://www.philosophydef.com/quotes/q0181.
Chicago: Protagoras. “Of all things the measure is man..” Philosophy Blind Box. Accessed 2026. https://www.philosophydef.com/quotes/q0181.
Frequently asked questions
What is the source of the quotation “Of all things the measure is man.”?
The passage is attributed to Protagoras, DK 80B1 (via Plato, Theaetetus). The archive attributes this English wording to DK 80B1 (via Plato, Theaetetus) and files it under Sophists. That locator distinguishes the passage from loose internet attributions: readers can return to the named work or section to check translation, surrounding argument, and edition-specific wording.
What does Protagoras mean by knowledge?
Epistemology asks whether knowledge is justified true belief, reliable tracking of the world, or something else; it also asks how perception, testimony, memory, and reason contribute. This passage enters that discussion through knowledge, humanity.