Most of their presocratic claims were speculations about the physical nature of the cosmos and its origins. In some ways, the presocratics might be viewed as the earliest natural scientists, with their strong interest in physics, chemistry, astronomy, geology, meteorology, and even psychology. Where earlier thinkers had given mythological or religious explanations of natural phenomena, attributing them to named gods, the first thinkers in the Ionian school were called physiologoi by Aristotle, because they offered accounts (logoi) for nature (phusis).

If we describe the great triad of traditional/modern/postmodern as mythos/logos/nomos, we can say that the presocratics abandoned the traditional myths in favor of modern reasoning about natural phenomena.

By contrast, Socrates/Plato changed the subject to ethical issues. The sophists argued that ethical problems are relative to the cultural values of a given community. They cannot be decided by reason. Science can discover how the world is (facts), but not how it ought to be (values). Values depend on the conventions and norms of a society, a question of nomos. Protagoras studied the norms of a community before writing their constitution for them. Protagoras was a postmodern thinker, probably the first. We make modern and postmodern a philosphical stance, not a temporal period.

It took Aristotle to return to cosmological, theological, and metaphysical issues first raised by the presocratic philosophers and the great epic writers like Homer and Hesiod. And in his great works on ethics, Aristotle sought universal principles. He was a modern thinker, who thought we can reason to values.

Thales of Miletus is regarded as the first Greek philosopher. To know anything, he advised, begin with advice, "Know thyself" This motto, γνῶθι σεαυτόν, was engraved on the facade of the Oracle of Apollo in Delphi. His cosmogony was that everything began as water.

For Anaximander of Miletus, a student of Thales, the first principle is a sort of indefinite and unbounded moving element, the apeiron (ἄπειρον). Unlike the other presocratics, he did not name a known specific element as the origin of all matter, like water (Thales), fire (Heraclitus), or air (Anaximenes). Anaximander may have been the first natural scientist, describing principles about the creation and destruction of order as an arrangement of things in time, which are created and later perish.

The two great antagonist views among the ancients were from Parmenides and Heraclitus. For Parmenides, "All is One," there is no such thing as nothing (the void of the atomists), and change is an illusion (all the Zeno paradoxes of motion attempted to support his master Parmenides's claims).

For Heraclitus, by contrast, "All is Flux." There is nothing but change. "You can't step in the same river twice." For his primal element, Heraclitus chose fire, because unlike Thales's water and Anaximines's air (and of course Earth), Fire is always rapidly changing.The one great positive insight of Heraclitus was that behind all changes there are laws – the "Logos." He clearly anticipates the modern notion of the laws of nature.

Aristotle gives great credit to several presocratic philosophers, starting with Thales of Miletus, for attempting "natural" explanations for phenomena where earlier thinkers had given only poetic, mythological, or theological stories. Although the explanations were very simple, they were as basic as could be. Thales said "All is Water." This means everything material now is somehow made from water. This is the sort of basic principle snd discovery of basic elements of nature that Aristotle was after.

For Anaximenes, another Milesian, the primal element from which all is made is air.

Pythagoras gave Plato the idea that mathematics could supply the most fundamental explanations of reality, namely the Forms, the organization and arrangement of things in the universe. Most other pre-Socratics were focused on material explanations, especially the atomists, Democritus and Leucippus, who were physical determinists, and Epicurus, who agreed about the atoms and void, but made the atoms swerve to add an element of indeterminism to events.

Among the Sophists, Protagoras was the greatest relativist, and can be regarded as the first postmodern. He travelled Greece to write constitutions for different city-states, not by following a perfectly rational and universal constitution suitable for all people as would a modern thinker, but by asking the citizens what their norms and practices should be. He is famously known for the relativistic idea that "man is the measure of all things," which recognizes that everything in culture is created by man.

The great sophist a href="/solutions/philosophers/gorgias/">Gorgias was an even greater relativist than Protagoras. He challenged the many physicists (φυσικοι) who 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:

• Things exist
• You can know what things exist
• You can tell others about what exists

Gorgias is reported to have dazzled and delighted his audiences by proving the opposites of these, by using nearly identical arguments:

• Nothing exists
• If by chance something did exist, you could not know anything about it
• If you did accidentally learn something about it, there is no way you could communicate your knowledge to others