Attributed to Parmenides
«Being is and non-being is not.»
Misattributed
Verdict
It is not in Parmenides's work
A textbook formula condensing B2 and B6, but not found as such in the poem. Parmenides says "is" with no expressed subject, and the nominalised "Being" is a later interpretation.
What they did say
Verified words of Parmenides
«Meet it is that thou shouldst learn all things, as well the unshaken heart of well-rounded truth, as the opinions of mortals in which is no true belief at all.»
DK 28 B1.28–30, en Sexto Empírico, Contra los matemáticos VII 111, y Simplicio, Comentario al Sobre el cielo 557. Griego: Diels-Kranz; inglés: John Burnet, Early Greek Philosophy (1908); español: traducción propia.
«The first, namely, that It is, and that it is impossible for it not to be, is the way of belief, for truth is its companion. The other, namely, that It is not, and that it must needs not be,—that, I tell thee, is a path that none can learn of at all.»
DK 28 B2.3–6, en Proclo, Comentario al Timeo I 345, y Simplicio, Comentario a la Física 116. Griego: Diels-Kranz; inglés: John Burnet, Early Greek Philosophy (1908); español: traducción propia.
«For it is the same thing that can be thought and that can be.»
DK 28 B3, en Clemente de Alejandría, Stromata VI 23, y Plotino, Enéadas V 1, 8. La construcción admite varias traducciones («lo mismo es lo que puede pensarse y lo que puede ser»). Griego: Diels-Kranz; inglés: John Burnet, Early Greek Philosophy (1908); español: traducción propia.