W. T. Stace, A critical history of Greek philosophy
“ In speaking of Parmenides, I pointed out that his teaching may be interpreted either in an idealistic or a materialistic sense, and that these two aspects of thought lie side by side in Parmenides, and that it is possible to emphasize either the one or the other. Empedocles seizes upon the materialistic side. The essential thought of Parmenides was that Being cannot pass into not-being, nor not-being into Being. Whatever is, remains for ever what it is. ”
