Ideas of Protagoras, by Theme

[Greek, c.481 - 411 BCE, Born at Abdera, in northern Greece. Died in Sicily.]

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6. Mathematics / A. Nature of Mathematics / 2. Geometry
No perceptible object is truly straight or curved
     Full Idea: No perceptible object is geometrically straight or curved; after all, a circle does not touch a ruler at a point, as Protagoras used to say, in arguing against the geometers.
     From: Protagoras (fragments/reports [c.441 BCE], B07), quoted by Aristotle - Metaphysics 998a1
11. Knowledge Aims / C. Knowing Reality / 2. Phenomenalism
Everything that exists consists in being perceived
     Full Idea: Everything that exists consists in being perceived.
     From: Protagoras (fragments/reports [c.441 BCE]), quoted by Didymus the Blind - Commentary on the Psalms (frags)
     A reaction: A striking anticipation of Berkeley's "esse est percipi" (to be is to be perceived).
13. Knowledge Criteria / D. Scepticism / 1. Scepticism
Protagoras was the first to claim that there are two contradictory arguments about everything
     Full Idea: Protagoras was the first to claim that there are two contradictory arguments about everything.
     From: report of Protagoras (fragments/reports [c.441 BCE], A1) by Diogenes Laertius - Lives of Eminent Philosophers 09.51
13. Knowledge Criteria / E. Relativism / 1. Relativism
There is no more purely metaphysical doctrine than Protagorean relativism
     Full Idea: No purer metaphysical doctrine can possibly be found than the Protagorean thesis that to be (anything at all) is to be relative ( to something or other).
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Josť A. Benardete - Metaphysics: the logical approach Ch.3
13. Knowledge Criteria / E. Relativism / 3. Subjectivism
You can only state the problem of the relative warmth of an object by agreeing on the underlying object
     Full Idea: Only if the thing that is cold to me is precisely identical with the thing that is not cold to you can Protagoras launch his argument, but then it is seen to be the thing in itself that exists absolutely speaking.
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Josť A. Benardete - Metaphysics: the logical approach Ch.8
If my hot wind is your cold wind, then wind is neither hot nor cold, and so not as cold as itself
     Full Idea: Because the wind is cold to me but not you, Protagoras takes it to in itself neither cold nor not-cold. Accordingly, I very much doubt that he can allow the wind to be exactly as cold as itself.
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Josť A. Benardete - Metaphysics: the logical approach Ch.8
13. Knowledge Criteria / E. Relativism / 6. Relativism Critique
God is "the measure of all things", more than any man
     Full Idea: In our view it is God who is pre-eminently the "measure of all things", much more so than any "man", as they say.
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Plato - The Laws 716c
Protagoras absurdly thought that the knowing or perceiving man is 'the measure of all things'
     Full Idea: When Protagoras quipped that man is the measure of all things, he had in mind, of course, the knowing or perceiving man. The grounds are that they have perception/knowledge, and these are said to be the measures of objects. Utter nonsense!
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Aristotle - Metaphysics 1053b
Relativists think if you poke your eye and see double, there must be two things
     Full Idea: In fact there is no difference between Protagoreanism and saying this: if you stick your finger under your eyes and make single things seem two, then they are two, just because they seem to be two.
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Aristotle - Metaphysics 1063a06
22. Metaethics / C. Ethics Foundations / 2. Source of Ethics / j. Ethics by convention
Early sophists thought convention improved nature; later they said nature was diminished by it
     Full Idea: Protagoras and Hippias evidently believed that convention was an improvement on nature, whereas later sophists such as Antiphon, Thrasymachus and Callicles seemed to contend that conventional morality was undermined because it was 'against nature'.
     From: report of Protagoras (fragments/reports [c.441 BCE]) by Fred D. Miller jr - Classical Political Thought
     A reaction: This gets to the heart of a much more interesting aspect of the nomos-physis (convention-nature) debate, rather than just a slanging match between relativists and the rest. The debate still goes on, over issues about the free market and intervention.
23. Ethics / B. Contract Ethics / 1. Contractarianism
For Protagoras the only bad behaviour is that which interferes with social harmony
     Full Idea: For Protagoras the only constraint on human behaviour is that it not interfere with social harmony, the essential condition for human survival.
     From: report of Protagoras (fragments/reports [c.441 BCE]) by David Roochnik - The Tragedy of Reason p.63
23. Ethics / C. Virtue Theory / 2. Elements of Virtue Theory / d. Teaching virtue
Protagoras contradicts himself by saying virtue is teachable, but then that it is not knowledge
     Full Idea: Protagoras claimed that virtue was teachable, but now tries to show it is not knowledge, which makes it less likely to be teachable.
     From: comment on Protagoras (fragments/reports [c.441 BCE]) by Plato - Protagoras 361b
25. Society / C. Social Justice / 5. Right to Punish / b. Retribution for crime
Protagoras seems to have made the huge move of separating punishment from revenge
     Full Idea: The distinction of punishment from revenge must be regarded as one of the most momentous of the conceptual discoveries ever made by humanity in the course of its slow, tortuous, precarious, emergence from barbaric tribalism. Protagoras originated it.
     From: report of Protagoras (fragments/reports [c.441 BCE]) by Gregory Vlastos - Socrates: Ironist and Moral Philosopher p.187
25. Society / E. State Functions / 4. Education / a. Education principles
He spent public money on education, as it benefits the individual and the state
     Full Idea: He used legislation to improve the condition of illiterate people, on the grounds that they lack one of life's great goods, and thought literacy should be a matter of public concern and expense.
     From: report of Protagoras (fragments/reports [c.441 BCE]) by Diodorus of Sicily - Universal History 12.13.3.3
25. Society / E. State Functions / 4. Education / b. Aims of education
Successful education must go deep into the soul
     Full Idea: Education does not take root in the soul unless one goes deep.
     From: Protagoras (fragments/reports [c.441 BCE], B11), quoted by Plutarch - On Practice 178.25
28. God / C. Attitudes to God / 5. Atheism
He said he didn't know whether there are gods - but this is the same as atheism
     Full Idea: He said that he did not know whether there were gods - but this is the same as saying that he knew there were no gods.
     From: comment on Protagoras (fragments/reports [c.441 BCE], A23) by Diogenes (Oen) - Wall inscription 11 Chil 2