In Plato’s Republic there is the Divided Line which is cut into two pieces which are related to Doxa (opinion, appearances) and Ratio (Reason). These are each again divided. Doxa is divided into grounded and ungrounded opinion. Ration is divided into representable (like mathematics) and non-representable intelligibles. So Doxa is what seems to be so, and ratio describes what IS so. These are each steps toward the Good which is the source of the variety of things that appear in the world. Thus there are two kinds of opinion, that which is are statements that are not backed up by anything, and statements which are grounded in some sort of evidence or by appeal to some authority. But these opinions are different from what Ratio can prove to be so, which is like geometrical proofs that once proven are always the same, and can be proven again and again. But Plato wants us to realize that there are things that the intellect can apprehend that are not representational like ideas and which cannot be proven but are a vision that guides us that we get by recognition and recall. Beyond that there is the sun of the Good which is the source of all variety which unfold into differences between things. We cannot look directly into the sun without being blinded. On the other hand there is the Cave where the Sophist is parading with things casting shadows on the wall that the prisoner sees. The difference between seeming to be so which is like the shadows, and the actual object which is being held by the Sophist is what is grounded with evidence or by authority asserted. But when the prisoner is forced to go up out of the cave he first sees reflection, and those are like the representable intelligibles, and then when he actually sees things it is like seeing the source forms of from which the representations are taken.
Note that the limit of the divided line on the side of Doxa is Paradox which when intensified becomes the Absurd. But the limit of the divided line on the side of Ratio is the superrational. The difference between them is that paradox is mixture of opposte things that can become contradictions, while the suprarational is when two things are apprehended together and exist at the same time but do not mix. We get superrational statements many times in Zen Koans, but they do not play a large a part in the Western tradition as do paradox and absurdity. Part of understanding the difference between Doxa and ratio is to understand that they define the suprarational nonduals. These are seen in the interpretations as either emptiness with the Buddhists or void with the Taoists. Both are opposite suprarational nonduals in their own way, and they are complementary to each other as striated and unstriated pairs.
Doxa is normally thought of as being fraught with illusion and delusion while ratio has a touchstone of proof that allows it to find a way out of illusion and delusion. So another way to look at the divided line is to see that Doxa is as far away from suprarational existence as you can get. And it is clear that the concept of Being itself is a great paradox, so the divided line stretches between Existence and Being. However, all of the divided line itself is in Being. Only its extreme limit is existence which can be interpreted as empty or void. So at each stage as we cross the divided line we are finding a different grade of Being as it tapers off into existence from the other extreme limit where it manifests its paradox or absurdity. So Doxa being close to the limit of paradox or absurdity is infected by that limit and cannot be trusted, and this closer region to the limit of Being as paradox is nearer to the heart of Being than the outward regions which are closer to existence which are rulled by ratio. So this turns on our heads the ideas that we are used to in Parmenides who talks about three ways, Being, Non-Being and Appearance. He says that of these three ways only Being actually is. Non-Being is Existence. And Appearance is between them. Note that even representable intelligibles and ideas are part of this Appearance. Representations are kinds of appearance that are very stable. Ideas are even more stable but do not have any kind of representation that captures them, because they are the same across languages for instance. But even ideas are kinds of appearances, as idea (edios) means to see. “The main words, εἶδος (eidos) and ἰδέα (idea) come from the Indo-European root *weid-, “see”.” (http://en.wikipedia.org/wiki/The…). This is why I say that Being is primarily illusion and delusion because the paradoxical limit is what is dominant in Being while the limit of existence is passive because it is what is projected on by the a priori projection mechanism of Being.
I hope this gives you some historical context for your question which will give it more meaning than it has on its own as a question out of the blue.