Gorgias is the author of a lost work: On Nature or the Non-Existent (also On Non-Existence). Rather than being one of his rhetorical works, it presented a theory of being that at the same time refuted and parodied the Eleatic thesis. The original text was lost and today there remain just two paraphrases of it. The first is preserved by the Pyrrhonist philosopher Sextus Empiricus in Against the Professors and the other by Pseudo-Aristotle, the author of On Melissus, Xenophanes, and Gorgias. Each work, however, excludes material that is discussed in the other, which suggests that each version may represent intermediary sources (Consigny 4). It is clear, however, that the work developed a skeptical argument, which has been extracted from the sources and translated as below:
Nothing exists; Even if something exists, nothing can be known about it; and Even if something can be known about it, knowledge about it can't be communicated to others. Even if it can be communicated, it cannot be understood. The argument has largely been seen as an ironic refutation of Parmenides' thesis on Being. Gorgias set out to prove that it is as easy to demonstrate that being is one, unchanging and timeless as it is to prove that being has no existence at all. Regardless of how it "has largely been seen" it seems clear that Gorgias was focused instead on the notion that true objectivity is impossible since the human mind can never be separated from its possessor.
"How can anyone communicate the idea of color by means of words since the ear does not hear colors but only sounds?" This quote was used to show his theory that 'there is nothing', 'if there were anything no one would know it', 'and if anyone did know it, no one could communicate it'. This theory, thought of in the late 5th century BC, is still being contemplated by many philosophers throughout the world. This argument has led some to label Gorgias a nihilist (one who believes nothing exists, or that the world is incomprehensible, and that the concept of truth is fictitious).
For the first main argument where Gorgias says, "there is no-thing", he tries to persuade the reader that thought and existence are not the same. By claiming that if thought and existence truly were the same, then everything that anyone thought would suddenly exist. He also attempted to prove that words and sensations could not be measured by the same standards, for even though words and sensations are both derived from the mind, they are essentially different. This is where his second idea comes into place.
Stolen from wikipedia