The late 6th or early 5th century BCE poet Parmenides of Elea was commonly regarded in the Greek tradition as a philosopher. Apparently his only work was a poem of 800 or so verses in epic hexameter form, of which about 160 are known from quotations in later authors, principally the commentary by the neoplatonist Simplicius on Aristotle’s Physics.
Parmenides may have been the first person to make strong claims purportedly grounded in nothing but pure reason. At the same time, he drew a sharp distinction between appearance and reality. He achieved notoriety among his fellow Greeks because his claims contradicted all experience. His disciple Zeno used Parmenidean principles to “prove” that arrows cannot fly, and that the speedy Achilles could never overtake a tortoise that had a head start.
According to Parmenides, we can “neither know, or attain to, or express, non-being”. He concluded from this that all distinction, becoming, and motion were mere appearances of “the way of error in which the ignorant and double-minded mortals wander. Perplexity of mind sways the erring sense. Those who believe Being and non-being to be the same, and then again not the same, are like deaf and blind men surprised, like hordes confusedly driven”.
“But the truth is only the ‘is’; this is neither begotten of anything else, nor transient, entire, alone in its class, unmoved and without end; it neither was, nor will be, but is at once the all. For what birth wouldst thou seek for it? How and whence should it be augmented? That it should be from that which is not, I shall allow thee neither to say nor to think, for neither can it be said or thought that the ‘is’ is not. What necessity had either later or earlier made it begin from the nothing? Thus must it throughout only be or not be; nor will any force of conviction ever make something else arise out of that which is not. Thus origination has disappeared, and decease is incredible. Being is not separable, for it is entirely like itself; it is nowhere more, else would it not hold together, nor is it less, for everything is full of Being. The all is one coherent whole, for Being flows into unison with Being: it is unchangeable and rests securely in itself; the force of necessity holds it within the bounds of limitation. It cannot hence be said that it is imperfect; for it is without defect, while non-existence is wanting in all” (quoted in Hegel, History of Philosophy vol. 1, Haldane trans., pp. 252-253).
Plato treats Parmenides with considerable respect, but fundamentally rejects his blunt teaching about being and non-being, replacing it with far subtler views, e.g., in The Sophist.
Aristotle says that Plato (and the atomist Democritus, whose writings are lost) were the first practitioners of extended philosophical argument, and I consider that the true beginning of philosophy; it seems to me Parmenides only made assertions and claimed they were grounded in pure reason. In his poem, the key claims are presented as revelations from a goddess. Much later, Kant would argue that nothing follows from pure reason alone.
According to Hegel’s History of Philosophy lectures, “This beginning is certainly still dim and indefinite, and we cannot say much of what it involves; but to take up this position certainly is to develop Philosophy proper, which has not hitherto existed”. Hegel says Spinoza tells us correctly that all determination is based on negation, but “Parmenides says, whatever form the negation may take, it does not exist at all” (p. 254). Spinoza scholars have criticized the claim about Spinoza, but in this context that is a side issue.
Hegel’s association of Parmenides with the beginning of philosophy needs to be understood in terms of his insistence on the inherent defectiveness of beginnings and the positive, provocative role of failures of thought. In differing degrees, Hegel also actually recognizes two other beginnings of philosophy as well — in the figurative thought of the world’s various religious traditions before Parmenides (who appears only halfway through volume 1 of Hegel’s History), and in the dialogues of Plato, with whom Hegel’s second volume begins. For Hegel, Parmenides’ bare thought of Being and denial of the basis of all determination represent an absolute failure of thought and an impossibility, but he nonetheless credits that failure and impossibility as having defined a problem that provoked all later development.
I consider it quite possible that Aristotle’s brief remarks about “being qua being” in two books of the Metaphysics were a kind of response to the Parmenidean problem. Traditionally, this has been claimed to be the subject matter of the Metaphysics, but both times Aristotle raises the problem explicitly, his discussion is limited to arguing for the moral necessity of the principle of noncontradiction, against the Sophists. In effect, he says that serious people must by definition take their commitments seriously, and therefore they do not contradict their own commitments.
Noncontradiction has a great importance for integrity in ethics, which was to be taken up anew by Kant and Hegel, with their emphasis on unity of apperception. But as Hegel points out explicitly in the Logic, pure being by itself is logically empty and sterile. In first philosophy, nothing follows from being qua being. (See also Hegel on Being.)