|Birth:||ca. 510 BC|
|Death:||ca. 450 BC|
|Notable ideas:||Being is, Eternal return, Appearance vs. Reality|
|Influenced:||Plato, Zeno of Elea, Melissus of Samos|
Parmenides of Elea (Greek: Παρμενίδης ὁ Ἐλεάτης, early 5th century BC) was an ancient Greek philosopher born in Elea, a Hellenic city on the southern coast of Italy. Parmenides was a student of Ameinias and the founder of the School of Elea, which also included Zeno of Elea and Melissus of Samos. According to Plato, Parmenides had been the erastes of Zeno when the latter had been a youth. 
Parmenides is one of the most significant of the pre-Socratic philosophers. His only known work, conventionally titled 'On Nature' is a poem, which has only survived in fragmentary form. Approximately 150 lines of the poem remain today; reportedly the original text had 3,000 lines. It is known, however, that the work originally divided into three parts:
The poem is a narrative sequence in which the narrator travels "beyond the beaten paths of mortal men" to receive a revelation from an unnamed goddess (generally thought to be Persephone) on the nature of reality. Aletheia, an estimated 90% of which has survived, and doxa, most of which no longer exists, are then presented as the spoken revelation of the goddess without any accompanying narrative.
The traditional interpretation of Parmenides' extremely obscure work is that he argued that the every-day perception of reality of the physical world (as described in doxa) is mistaken, and that the reality of the world is 'One Being' (as described in aletheia): an unchanging, ungenerated, indestructible whole. Under 'way of seeming', Parmenides set out a contrasting but more conventional view of the world, thereby becoming an early exponent of the duality of appearance and reality. For him and his pupils the phenomena of movement and change are simply appearances of a static, eternal reality.
Parmenides' philosophy is presented in verse. The philosophy he argued was, he says, given to him by a goddess, though the "mythological" details in Parmenides' poem do not bear any close correspondence to anything known from traditional Greek mythology:
It is with respect to this religious/mystical context that recent generations of scholars such as Alexander P. Mourelatos, Charles H. Kahn, and the controversial Peter Kingsley have begun to call parts of the traditional, rational logical/philosophical interpretation of Parmenides into question. According to Peter Kingsley Parmenides practiced iatromancy. It has been claimed, for instance, that previous scholars placed too little emphasis on the apocalyptic context in which Parmenides frames his revelation. As a result, traditional interpretations have put Parmenidean philosophy into a more modern, metaphysical context to which it is not necessarily well suited, which has led to misunderstanding of the true meaning and intention of Parmenides' message. The obscurity and fragmentary state of the text, however, renders almost every claim that can be made about Parmenides extremely contentious, and the traditional interpretation has by no means been completely abandoned.
Parmenides' considerable influence on the thinking of Plato is undeniable, and in this respect Parmenides has influenced the whole history of Western philosophy, and is often seen as its grandfather. Even Plato himself, in the Sophist, refers to the work of "our Father Parmenides" as something to be taken very seriously and treated with respect. In the Parmenides the Eleatic philosopher, which may well be Parmenides himself, and Socrates argue about dialectic. In the Theaetetus, Socrates says that Parmenides alone among the wise (Protagoras, Heraclitus, Empedocles, Epicharmus, and Homer) denied that everything is change and motion.
Parmenides is credited with a great deal of influence as the author of an "Eleatic challenge" that determined the course of subsequent philosophers' enquiries. For example, the ideas of Empedocles, Anaxagoras, Leucippus, and Democritus have been seen as in response to Parmenides' arguments and conclusions.
The Way of Truth discusses that which is real, which contrasts in some way with the argument of the Way of Seeming, which discusses that which is illusory. Under the Way of Truth, Parmenides stated that there are two ways of inquiry: that it is, that it is not. He said that the latter argument is never feasible because nothing can not be:
There are extremely delicate issues here. In the original Greek the two ways are simply named "that Is" (hopos estin) and "that Not-Is" (hos ouk estin) (Frag. 2. 3 and 2. 5) without the "it" inserted in our English translation. In ancient Greek, which, like many languages in the world, does not always require the presence of a subject for a verb, "is" functions as a grammatically complete sentence. A lot of debate has been focused on where and what the subject is. The simplest explanation as to why there is no subject here is that Parmenides wishes to express the simple, bare fact of existence in his mystical experience without the ordinary distinctions, just as the Latin "pluit" and the Greek uei ("rains") mean "it rains"; there is no subject for these impersonal verbs because they express the simple fact of raining without specifying what is doing the raining. This is, for instance, Hermann Fraenkel's thesis (Dichtung und Philosophie des fruehen Griechentums, 1962)  But many scholars still reject this explanation and have produced more complex metaphysical explanations. Since existence is an immediately intuited fact, non-existence is the wrong path because something cannot ever disappear just as something cannot ever come from nothing. In such mystical experience (unio mystica), however, the distinction between subject and object disappears along with the distinctions between objects, in addition to the fact that if nothing cannot be, it cannot be the object of thought either:
Thus, he concluded that "Is" could not have "come into being" because "nothing comes from nothing." Existence is necessarily eternal. (Parmenides, therefore, with many other early philosophers in both the East and West, was struggling with a principal law of nature which today is formulated as the conservation of mass-energy. The physicist Alan Guth has said this in the beginning of his book The Inflationary Universe.)
Moreover he argued that movement was impossible because it requires moving into "the void", and Parmenides identified "the void" with nothing, and therefore (by definition) it does not exist. That which does exist is The Parmenidean One which is timeless, uniform, and unchanging:
Parmenides claimed that the truth cannot be known through sensory perception. Only pure reason (Logos) will result in the understanding of the truth of the world. This is because the perception of things or appearances (the doxa) is deceptive. We may see, for example, tables being made from wood and destroyed, and speak of birth and demise; this belongs to the superficial world of movement and change. But this genesis-and-destruction, as Parmenides emphasizes, is illusory, because the underlying material of which the table is made will still exist after its destruction. What exists must always exist. And we arrive at the knowledge of this underlying, static, and eternal reality (aletheia) through reasoning, not through sense-perception.
After the exposition of the arche, i.e. the origin, the necessary part of reality that is understood through reason or logos (that [it] Is) , in the next section, the Way of Appearance/Opinion/Seeming, Parmenides proceeds to explain the structure of the becoming cosmos (which is an illusion, of course) that comes from this origin.
The structure of the cosmos is a fundamental binary principle that governs the manifestations of all the particulars: "the aither fire of flame" (8, 56), which is gentle, mild, soft, thin and clear, and self-identical -- this is something like the masculine principle -- and the other is "ignorant night", body thick and heavy -- this is something like the feminine principle. Thus Parmenides' cosmogony is exactly like the yin-yang picture in Chinese cosmogony.
The structure of the cosmos then generated is recollected by Aetius (II, 7, 1):
Only nineteen fragments of Parmenides' poem have survived into the modern era. All nineteen fragments were transcribed from Greek to German by a German paleographer named Hermann Diels in the 19th century. In fact, Diels assembled a document that entailed most of the known pre-Socratic philosophical writings. One important fragment in Parmenides' poem includes the notion that being is and as such it cannot be divided. Parmenides also teaches that in order to truly exist, one must look beyond appearances. For Parmenides, one way to go beyond the physical world was to meditate. Fragment III of the poem for example entails the idea of thinking and being as one and the same. Graduate students of philosophy have written thousand page dissertations on Fragment III alone. Upon further investigation into Parmenides' poem, one will find the underpinnings of Greek determinism. In other words, fate is the driving force behind the universe and thus free will is a mere figment of the human imagination. In the 19th century, Hegel incorporated this notion of Greek determinism into his philosophy of history.
Extensive bibliographies are available here and here.