The section known as "the way of truth" discusses that which is real and contrasts with the argument in the section called "the way of opinion," which discusses that which is illusory. Under the "way of truth," Parmenides stated that there are two ways of inquiry: that it is, on the one side, and that it is not.[14] on the other side. He said that the latter argument is never feasible because there is no thing that can not be:
For never shall this prevail, that things that are not are. (B 7.1)
There are extremely delicate issues here. In the original Greek the two ways are simply named "that Is" (ὅπως ἐστίν) and "that Not-Is" (ὡς οὐκ ἐστίν) (B 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. Much 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 huei (ὕει "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 Fränkel's thesis.[15] 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 a thing cannot disappear, just as something cannot originate 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:
Thinking and the thought that it is are the same; for you will not find thinking apart from what is, in relation to which it is uttered. (B 8.34–36)
For to be aware and to be are the same. (B 3)
It is necessary to speak and to think what is; for being is, but nothing is not. (B 6.1–2)
Helplessness guides the wandering thought in their breasts; they are carried along deaf and blind alike, dazed, beasts without judgment, convinced that to be and not to be are the same and not the same, and that the road of all things is a backward-turning one. (B 6.5–9)
Thus, he concluded that "Is" could not have "come into being" because "nothing comes from nothing". Existence is necessarily eternal. That which truly is [x], has always been [x], and was never becoming [x]; that which is becoming [x] was never nothing (Not-[x]), but will never actually be. Parmenides was not struggling to formulate the laws of conservation of mass and conservation of energy; he was struggling with the metaphysics of change, which is still a relevant philosophical topic today.
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:
How could what is perish? How could it have come to be? For if it came into being, it is not; nor is it if ever it is going to be. Thus coming into being is extinguished, and destruction unknown. (B 8.20–22)
Nor was [it] once, nor will [it] be, since [it] is, now, all together, / One, continuous; for what coming-to-be of it will you seek? / In what way, whence, did [it] grow? Neither from what-is-not shall I allow / You to say or think; for it is not to be said or thought / That [it] is not. And what need could have impelled it to grow / Later or sooner, if it began from nothing? Thus [it] must either be completely or not at all. (B 8.5–11)
[What exists] is now, all at once, one and continuous... Nor is it divisible, since it is all alike; nor is there any more or less of it in one place which might prevent it from holding together, but all is full of what is. (B 8.5–6, 8.22–24)
And it is all one to me / Where I am to begin; for I shall return there again. (B 5)
Perception vs. Logos[edit]
Parmenides claimed that there is no truth in the opinions of the mortals. Genesis-and-destruction, as Parmenides emphasizes, is a false opinion, because to be means to be completely, once and for all. What exists can in no way not exist.
For this view, that That Which Is Not exists, can never predominate. You must debar your thought from this way of search, nor let ordinary experience in its variety force you along this way, (namely, that of allowing) the eye, sightless as it is, and the ear, full of sound, and the tongue, to rule; but (you must) judge by means of the Reason (Logos) the much-contested proof which is expounded by me.