Parmenides (c. 485 BCE) was a Greek philosopher from the colony of Elea in southern Italy. He is known as the founder of the Eleatic School of philosophy which taught a strict Monistic view of reality. Philosophical Monism is the belief that all of the sensible world is of one, basic, substance and being, un-created and indestructible. According to the ancient writer Diogenes Laertius (c. 200 CE), Parmenides was a student of Xenophanes of Colophon (who some claim as the founder of the Eleatic School) but left his master’s discipline to pursue his own vision. Even so, the stamp of Xenophanes’ teachings can be seen in the work of Parmenides in that both assert that the things in life which one thinks one understands may be quite different than they seem to be, especially regarding an understanding of the gods. Xenophon's insistence on a single deity, who in no way resembled human beings, seems to have been the basis for Parmenides' claim of a single substance comprising all of reality. Parmenides was a younger contemporary of Heraclitus who claimed that all things are constantly in motion and change (that the basic `stuff' of life is change itself). Parmenides’ thought could not be further removed from that of Heraclitus in that Parmenides claimed nothing moved, change was an impossibility, and that human sense perception could not be relied upon for an apprehension of Truth.
According to Parmenides, “There is a way which is and a way which is not” (a way of fact, or truth, and a way of opinion about things) and one must come to an understanding of the way “which is” to understand the nature of life. Known as the Philosopher of Changeless Being, Parmenides' insistance on an eternal, single Truth and his repudiation of relativism and mutability would greatly influence the young philosopher Plato and, through him, Aristotle (though the latter would interpret Parmenides’ Truth quite differently than his master did). Plato devoted a dialogue to the man, the Parmenides, in which Parmenides and his student, Zeno, come to Athens and instruct a young Socrates in philosophical wisdom. This is quite an homage to the thought of Parmenides in that, in most dialogues, Plato presents Socrates as the wise questioner who needs no instruction from anyone. While Parmenides was an older contemporary of Socrates, it is doubtful the two men ever met and Plato's dialogue is considered an idealized account of the philosopher (though accurate in portraying his philosophy). Zeno of Elea was Parmenides' most famous student and wrote forty paradoxes in defense of Parmenides’ claim that change – and even motion – were illusions which one must disregard in order to know the nature of oneself and that of the universe.
Nothing is capable of inherently changing in any significant fashion because the very substance of reality is unchangeable and 'nothingness' cannot be comprehended.
Zeno's work was intended to clarify and defend Parmenides' statements, such as, "There is not, nor will there be, anything other than what is since indeed Destiny has fettered it to remain whole and immovable. Therefore those things which mortals have established, believing them to be true, will be mere names: "'coming into being and passing away,' 'being and not being,' 'change of place'..."(Robinson, 116). In other words, Parmenides argues that we may think the world we live in is comprised of multiples but, in reality, it is One. Nothing is capable of inherently changing in any significant fashion because the very substance of reality is unchangeable and 'nothingness' cannot be comprehended.
Even so, it seems that Parmenides' ideas themselves were hard to comprehend for his listeners, necessitating Zeno's mathematical paradoxes. Parmenides' main point, however, was simply that nothing could come from nothing and that `being' must have always existed. He writes:
There is left but this single path to tell thee of: namely, that being is. And on this path there are many proofs that being is without beginning and indestructible; it is universal, existing alone, immovable and without end; nor ever was it nor will it be, since it now is, all together, one, and continuous. For what generating of it wilt thou seek out? From what did it grow, and how? I will not permit thee to say or to think that it came from not-being; for it is impossible to think or to say that not-being is.
What would then have stirred it into activity that it should arise from not-being later rather than earlier? So it is necessary that being either is absolutely or is not. Nor will the force of the argument permit that anything spring from being except being itself. Therefore justice does not slacken her fetters to permit generation or destruction, but holds being firm. (Fairbanks, 93)
Simply put, his argument is that since `something' cannot come from `nothing' then `something' must have always existed in order to produce the sensible world. This world we perceive, then, is of one substance - that same substance from which it came - and we who inhabit it share in this same unity of substance. Therefore, if it should appear that a person is born from `nowhere' or that one dies and goes somewhere else, both of these perceptions must be wrong since that which is now can never have been `not' nor can it ever `not be'. In this, Parmenides may be developing ideas from the earlier philosopher Pythagoras (c. 571-c.497 BCE) who claimed the soul is immortal and returns to the sensible world repeatedly through reincarnation. If so, however, Parmenides very radically departed from Pythagorean thought which allows that there is plurality present in our reality.
To Parmenides, and his disciples of the Eleatic School, such a claim would be evidence of belief in the senses which, they insisted, could never be trusted to reveal the truth. The Eleatic principle that all is one, and unchanging, exerted considerable influence on later philosophers and schools of thought. Besides Plato (who, in addition to the dialogue Parmenides also addressed Eleatic concepts in his dialogues of the Sophist and the Statesman) the famous Sophist Gorgias employed Eleatic reasoning and principles in his work as Aristotle would also do later, principally in his Metaphysics.