As is the case with Existentialism, the basic principles which underlie nihilism existed long before there was a term that attempted to describe them as a coherent whole. In the case of nihilism, most of the basic principles can be found in the development of ancient skepticism among the ancient Greeks.
Often portrayed as the original skeptic, and perhaps also the original nihilist, was Gorgias (483-378 BCE) who is famous for having said: "Nothing exists. If anything did exist it could not be known. If it was known, the knowledge of it would be incommunicable." This was a radical reversal of many of people's common assumptions and it remains a radical challenge even today.
Gorgias was not technically a "skeptic" in the sense of being part of the skeptical school of philosophers — he was instead a Sophist. The philosophers who belonged more or less explicitly to the Skeptical school of philosophy were known in ancient Greece as the "Skeptikoi." The term comes from the Greek verb skeptomai which means "to look carefully, to reflect."
The Skeptics regarded the basic principle of their outlook as epistemological skeptikoi or caution. They were adamant about not making statements which might be proven false and which they could not prove absolutely true. Because that included just about everything, their ultimate conclusion tended to be that everything usually treated as "knowledge" is really just opinion and nothing is really "true."
The first "Philosophical Skeptic" is generally regarded as Pyrrho (c. 360 — c.270 BCE), a man about whom relatively little is known; but we do have some information about his ideas through later followers. According to one of his students, Timon of Phlius, Pyrrho argued that everything around us is equally indifferent (adiaphora), unmeasurable (astathmêta), and indeterminate (anepikrita). Neither our senses nor our opinions really inform us of the truth of the world — no matter what we believe, someone equally clever and intelligent believes the exact opposite. The only conclusion then is to have no opinion in the first place and remain uncommitted.
Most members of the skeptical school of philosophy argued for what might be called "epistemological skepticism" — their focus was upon the reliability of our senses and therefore our ability to make knowledge claims about the world around us. A number of Greek philosophers, for example Heraclitus, Parmenides, Democritus, Empedocles, and Anaxagoras, came to argue that our senses were not reliable sources of factual information.
This is not to say, however, that discussion about values was entirely neglected by the Skeptics. Another philosopher who has become famous for his skeptical position was Protagoras (480-411 BCE). He is remembered for having said that "Man is the measure of all things," a statement generally interpreted to mean that there are not objective, absolute standards that exist external to human beings. Instead, all standards by which things might be measured (including our values) must come from within human beings and are dependent upon our circumstances and situations.
This sort of philosophical skepticism, whatever form it took, became an important influence on all of Greek philosophy that followed. It is arguable that most of Western philosophy as a whole can be best understood as an attempt to demonstrate that knowledge is possible and that adequate grounds for justifying beliefs exist. In other words, much of philosophy involves attempts to refute or at least forestall the critiques of radical skepticism.
