Man is the measure of all things
From The Art and Popular Culture Encyclopedia
The full dictum reads "Man is the measure of all things: of things which are, that they are, and of things which are not, that they are not". Like many fragments of the Presocratics, this phrase has been passed down to us without any context, and its meaning is open to interpretation. However, the use of the word χρήματα (chrēmata) instead of the general word ὄντα (onta, entities) signifies that Protagoras was referring to things that are used by or in some way related to humans. This makes a great difference in the meaning of his aphorism. Properties, social entities, ideas, feelings, judgements, etc. are certainly χρήματα and hence originate in the human mind. However, Protagoras has never suggested that man must be the measure of the motion of the stars, the growing of plants or the activity of volcanoes.
"πάντων χρημάτων μέτρον ἐστὶν ἄνθρωπος, τῶν μὲν ὄντων ὡς ἔστιν, τῶν δὲ οὐκ ὄντων ὡς οὐκ ἔστιν"