Parmenides : BEING IS ALL THERE IS

2
Come then, I'll tell you, and take the tale with you after you've heard. Which alone are the ways of search, let us think. The one way, that there is being and there is not non-being, this is Persuasion's way - since it follows truth. The other, that there is not and it needs be not, which I tell you is a totally unwitting way; since you wouldn't know what does not exist - because it is not possible - nor would you speak of it. 

3
The same is thinking and being.

2
εἰ δ΄ ἄγ΄ ἐγὼν ἐρέω͵ κόμισαι δὲ σὺ μῦθον ἀκούσας͵ αἵπερ ὁδοὶ μοῦναι διζήσιός εἰσι νοῆσαι· ἡ μὲν ὅπως ἔστιν τε καὶ ὡς οὐκ ἔστι μὴ εἶναι͵ Πειθοῦς ἐστι κέλευθος (Ἀληθείηι γὰρ ὀπηδεῖ)͵ ἡ δ΄ ὡς οὐκ ἔστιν τε καὶ ὡς χρεών ἐστι μὴ εἶναι͵ τὴν δή τοι φράζω παναπευθέα ἔμμεν ἀταρπόν· οὔτε γὰρ ἂν γνοίης τό γε μὴ ἐὸν (οὐ γὰρ ἀνυστόν) οὔτε φράσαις.

3
τὸ γὰρ αὐτὸ νοεῖν ἐστίν τε καὶ εἶναι.