With Protagoras of Abdera, the period of Classical Philosophy begins.

This period marks a new philosophical vision centered on the anthropological question, that is: what is man? What can he know? What human acts can be considered just or unjust?

The question about arche and physis, which philosophers such as Thales of Miletus, Anaximander and Anaximenes sought to answer, is left somewhat aside.

Protagoras turns his reflection on man’s ability to know.

Biography of Protagoras

Protagoras was a sophist philosopher born in the city of Abdera (Thrace) in 491 B.C. and died in a shipwreck in 420 B.C.

Protagoras was the founder of the philosophical doctrine of relativism, which states that we have no absolute criteria for judging whether something is false or true.

He was accused of impiety or atheism, because he claimed that religions and gods were human conventions.

Protagoras traveled all over Greece, being several times in Athens; he was very prestigious by politicians. Pericles, the famous Statesman of the city of Athens, asked Protagoras to draft new legislation for the Pan-Hellenic colony of Tury.


Protagoras of Abdera is said to have written a work called The Antilogies, but it has been lost, with only a few fragments and testimonies remaining.

Other works attributed to him:

  • On Truth and Being;
  • On the Gods: a work that was possibly used to accuse him of impiety;

The relativism of Protagoras

Protagoras defended the philosophical relativism which consists in affirming that human knowledge has no criterion that can establish the truth or falsity of statements. For him, everything is relative.

His famous phrase illustrates well his relativistic doctrine, it says that:

Man is the measure of all things: of things which are, that they are, and of things which are not, that they are not.

By “measure,” Protagoras means “rule” or “norm,” that which establishes something; and “all things,” he means all human facts and experiences. Man is, therefore, the ultimate rule of all knowledge.

This phrase, which became known as the principle of relativism, and became famous among all relativistic philosophers in the West.

With this principle, Protagoras denies any kind of philosophical doctrine that establishes an absolute criterion that can distinguish true from false.

The only criterion is man, or rather, each individual human being. Each one is his own criterion to define what is right and wrong, true or false.

Therefore, Protagoras stated the following:

As each thing appears to me, so it is to me; as it appears to you, so it is to you. To him who is cold, it is cold; to him who is not cold, it is not.

In other words, Protagoras holds that each one establishes his own truth.

How can a weak argument be made stronger?

Because of his relativism, Protagoras said it was possible to make a weak argument become strong.

However, Protagoras was not in favor of using this to defend injustices; he taught this as a rhetorical technique or methodology, to show how it was possible to successfully defend an argument that in certain circumstances might be weak.

Therefore, this technique would allow any opinion to prevail against the opposing opinion.

This technique of Protagoras, encouraged the young people of his time to enter political life, in the courts or in the Greek assemblies, where a good argument was always well regarded and necessary.

Protagoras’ Morals

Once it is established that there is no absolute criterion for determining true and false, there is also no criterion for determining good and evil.

Therefore, because of relativism, Protagoras is forced to assert that there are no absolute moral values.

To get out of this inconvenience, Protagoras advocates a kind of moral utilitarianism. For each practical situation in life, there is something that is more convenient to do, something more opportune. The wise man is precisely the one who knows what is useful and more convenient, and knows how to convince others to recognize what is more opportune.

In this case, evil and good are understood as something “useful”, “less harmful” to the individual.

Cite This Work

Vieira, S. (2021, December 06). Protagoras. Filosofia do Início. Retrieved from

Vieira, Sadoque. “Protagoras.” Filosofia do Início, December 6, 2021.

Vieira, Sadoque. “Protagoras.” Filosofia do Início, 6 Dec. 2021,

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