Parmenides’ poem had left hisdisciples with the grave task of finding a solution to the problem of “non-Being”, that is, finding an answer to the question about the relationship between Being and its denial. If, as we have seen, the Parmenidean Being is what one must necessarily preach “is, and cannot not be”, how should one understand all the transient, mutable and becoming realities of which one makes sensitive experience in the world? A work of real rescue is necessary: one must “save the phenomena”, subtract the Becoming from the fall in the field of non-Being.
The task falls to the Stranger of Elea, a fictitious character – a pupil of Parmenides on a visit to Athens – who in the dialogue “The Sophist” Plato puts in discussion with the young Theaetetus. The title is an indication of the first content of the speech; the question that guides the dialogue is in fact: “who is the Sophist?” It will be precisely from the search for such a definition that the answer to the fundamental ontological question will appear.
After finding six different definitions of “sophist”, the research turns to investigate the nature of the latter’s discourses. In fact, he teaches many things to the young people of the cities in return for payment, but these are not always “according to truth”; however, at this point the fundamental problem emerges:
Being is the Truth, therefore thinking or saying the non-Being (-Truth) is equivalent to thinking and saying the impossible.
The question is simple only at first sight; the Platonic reasoning, in fact, continues in this way: an image is a semblance of reality (of the Truth), and yet it is not reality itself, since, precisely, it is only its image. If reality is the Truth (the real with respect to the unreal), then what “is not true” is contrary to the Truth, and therefore is false. The Truth, moreover, is the essential, what-is, and therefore the untrue will be something that is not, that is, the non-Being. Everything is complicated when the theme of falsehood is also approached: “[…] an erroneous or false reasoning will be considered as such for the same reasoning: inasmuch as it affirms that what it is, is actually not; as well as inasmuch as it affirms that what it is not, is”.
To say of the Sophist that he produces fallacious images of reality is to say that non-Being in some way is, and that being in some way is not. If, in fact, Parmenides’ position is held firm, then something like the fictitious appearances of reality and falsity or error could not exist. Being is the Truth, therefore thinking or saying the non-Being (-Truth) is equivalent to thinking and saying the impossible, because the way of non-Being is imperceptible. Because the non-being is the unthinkable and the unspeakable (outside the field of Being, that is, of the Whole). The Sophist, therefore, in his defence against the accusation of being a “charlatan”, manages to make the opponent say that the non-Being in some way is, and the Being in some way is non-Being. In fact, either the Sophist lies, and then whoever accuses him of lying admits the non-Being, or Parmenides’ position is held firm and it is impossible to accuse the Sophist of falsehood, no matter what he claims. In the face of such a radical dichotomy, the Stranger is forced to act on the position of his own master:
Guest – But then with much greater warmth I should address a prayer to you.
Theae. – What prayer?
Guest – I would not want you to see in me an evil parricide.
Theae. – Why?
Guest – If I have to persist in trying to defend myself against the Sophist, it will be inevitable that I submit to careful testing the system of Parménide, my father. I will find myself forced to make strength in my demonstration and to conclude that not being in a certain sense is to be and that being reciprocally is not to be in a certain sense.
[The Sophist, 241, d1-d10]
At this point, the discussion becomes tight and complex, and it would be difficult and lengthy to deal with each step here. That is why we will only deal with the fundamental ones.
The first point to be made is that the Being is One, because if it were many, any otherness with respect to it would necessarily fall into non-being. The second is the need to preserve the presence of the intellect in Being; in fact, every search for knowledge depends on the intellect, including the latter.
In order to give intellect it is necessary to give both motion and immobility; in fact, in the workings of the intellect it is necessary both the movement of argumentation and the immobility of premises or principles.
“Quietness” and “motion”, therefore, constitute Being, and therefore they are, but at the same time they are not in identity with it, because if Being were in identity with both quietness and movement it would become an immovable-mobile and therefore something impossible: “Guest – Then movement and quietness, taken as a whole, are not being. Being is something different from one and the other”. It will therefore be necessary to investigate whether it is possible that to the same name (Being) are attributed different precepts, even when they are one the opposite of the other (quiet-motion).
The answer is that preaching can take place for certain preachings and not for others, i.e. it is possible to preach of the same name some things and not others, i.e. in some cases the process of participation is possible and in others not.
It has therefore come to recognize as necessary the existence of at least three fundamental genders: Being, stillness, becoming. The next observation is that it is not possible to identify quietness and motion among them, and in the same way it is not possible that they are the same as Being. In other words, stillness is evidently not motion and vice versa, and Being is not in identity neither with stillness nor with motion (otherwise it would be at the same time in stasis and motion, and this would be absurd) but between it and the other two there is a relationship of participation: stillness participates of Being and motion equally. Between stillness and motion, instead, participation is impossible, and their relationship will be one of contrariety or, more precisely, otherness.
The answer is that “same” and “other” are two genres which, like “stillness” and “motion”, participate in the Being, but are opposed to each other. None of them identifies with Being, and none of them is identical with another: the relationship of otherness exists between one gender and another, while the relationship of similarity exists between one gender and itself; each gender is the same with itself and another with others. Therefore, Being is composed of “five supreme genders” with their particular relationships – and this is because five is the least possible number of genders to be accepted in order to reason about Being.
Let us now tighten the knots of argumentation to get to the focal point; we shall use the words of Plato himself:
As participants in Being things are; as different, other, than Being things are not Being, and therefore they are not. This is the difficulty to overcome, on the basis of all the reasoning done so far. Plato’s answer is, at first sight, simple but actually of unimaginable importance for the future of human thought, because on the basis of our way of understanding what Being is and what non-being is we have built the world as we know it today. Let us read his words:
There are therefore two types of not being: the not being relative (heteron), that is, not being something because you are different from that thing, and yet you remain something “that is”; the not being absolute (enantion), that is, not being as opposed to Being, that is, nothingness. Plato shows us how the expression “not to be” (and therefore, in general, the negative form “not”) contains in itself two very different meanings: one is otherness,the other is contrariety. The different from Being is still a being (it is a non-being-the-medesimo, and therefore the Being-other), while the opposite of being is the non-being (the non-being-Being, the n-entity, the nothingness).
Everything, every entity, is therefore fragmented with non-being, because everything is in otherness with respect to the others, and in this sense it contains the non-being (-other). Error and falsehood, therefore, are present in discourses when there is wrong preaching in them, that is, ideas are put together that should not be juxtaposed. To deny these fallacious chains of ideas does not mean to deny the Being, but to deny that speech that says of something the things that are not (that do not belong to it) instead of the things that are.
We do not have the space, here, to demonstrate how much this platonic solution has influenced all philosophical thought and not only, but has in a certain sense built the very way of thinking that we still apply today when we live in the world and when, with our Technique, we create it.
We conclude, however, giving for the last time the word to (our) Guest of Elea, who speaks to his interlocutors and speaks to us, to you, to remind us what it means to reason together on these issues, and touch with the mind these peaks:
 All quotations herein come from the translation of Plato’s Sophist by Benjamin Jowett.