Gorgias was one of the early "pre-Socratic" philosophers that Socrates labelled as Sophists. Another was Gorgias' contemporary, Protagoras. These two were both the subjects of Platonic dialogues. It was a commonplace for natural philosophers, the earliest scientists, to give lectures on the nature of things, proving that things exist, that we can have knowledge of them, and that we can communicate that knowledge through teaching. Gorgias and Protagoras were critics of the Eleatic philosophers, especially Parmenides, who was Plato's inspiration for the idea that Truth must be eternal. Parmenides argued that Being must be unchanging. Being cannot be generated from nothing, nor can it cease to be. Heraclitus disagreed, saying that everything was constantly changing ("All is flux" and "you cannot step in the same river twice"), but he held there was a "logos" governing change. In that respect, he anticipated the laws of nature. The Eleatics were pre-cursors of the modern rationalists (Descartes, Spinoza, and Leibniz). Thomas Aquinas was a scholastic intermediary. They believed everything about the world could be deduced from first principles, working in an "ivory tower." They were especially critical of the nature philosophers (physiologoi), who thought that knowledge could be gained by observing the material world. Perceptions of phenomena are unreliable, they said. Such knowledge is merely conventional, relative to each observer, not certain. The goal of philosophy is certain knowledge and truth. The early materialist/physicalist philosophers Democritus and his teacher Leucippus replaced theological and supernatural explanations of phenomena with natural materialist explanations. They assumed the world was completely made of matter, which they postulated to consist of just a few types of invisible particles that could be combined to make all of the visible objects, their properties, and their behaviors. The fundamental elements of their time - earth, water, air, and fire - were in turn simply compounds of sub-elementary particles they called atoms (indivisibles) in a void or vacuum between the atoms.
"By convention hot, by convention cold, but in reality atoms and void."Parmenides had denied the possibility of the void with the simple logical/language argument that if "nothing" was between two bodies, it follows that they must be in contact with one another. Plato and Aristotle generally preferred Parmenides' idea of a continuous filled plenum and opposed the atomists' ideas of discrete particulate objects separated by nothing. Democritus denied the arbitrariness of phenomena that was implied if they were the free actions of the gods. He replaced that explanation with the idea of deterministic laws governing the behavior of the atoms, and as a consequence explaining all phenomena made of atoms, including human beings and their actions. Leucippus had denied that anything happened at random (μάτην),
"Nothing occurs at random, but everything for a reason and by necessity."Gorgias' colleague Protagoras accepted the criticism of phenomena as merely conventional. The same wind might seem warm to one man and cool to another. But their perceptions of the phenomena are equally valid. "Man is the measure of all things," he said, where things (χρημα) refers to physical phenomena. In his
And it is utterly silly, when we are looking for a definition of knowledge, to say that it is right opinion with knowledge, whether of difference or of anything else whatsoever. So neither perception, Theaetetus, nor true opinion, nor reason or explanation combined with true opinion could be knowledge (epistéme).Gorgias was in some sense a skeptic, an early post-modern thinker, even a deconstructionist as to the power of language. He expressly used the language, the rhetorical style, and the arguments of the Eleatics to refute their claims about Being (το ον) and their denial of the existence of Non-Being (το μη ον) He and Protagoras can be seen as attacking the view that thought alone can establish true knowledge. One must look at the world of material things. In this respect they are precursors of the modern empiricists (Locke, Berkeley, and Hume). Their medieval predecessor was John Duns Scotus, who insisted that the freedom of God meant that one had to look at the world to understand it. Despite the ancient Stoic dicta that God is Nature and that God is Reason, one can not understand the world with reason alone. Many ancient physicists (φυσικοι, φυσιολογοι) lectured and wrote on "what there is" in treatises called "Peri Physis" (Περι Φύσις) - roughly, About Nature, or The Nature of the Physical World. The content of the typical physicist/philosopher lectures was usually in three parts: