Editing First principle (section)

==== Ionian school ====
The earliest Pre-Socratic philosophers, the Ionian material monists, sought to explain all of nature ([[physis]]) in terms of one unifying ''arche.'' Among the material monists were the three Milesian philosophers: [[Thales]], who believed that everything was composed of water; [[Anaximander]], who believed it was ''[[apeiron (cosmology)|apeiron]]''; and [[Anaximenes of Miletus|Anaximenes]], who believed it was air.  This is considered as a permanent substance or either one or more which is conserved in the generation of rest of it. From this all things first come to be and into this they are resolved in a final state. This source of entity is always preserved.<ref>[[Aristotle]]-Metaph.A, 983, b6ff).</ref> Although their theories were primitive, these philosophers were the first to give an explanation of the physical world without referencing the supernatural; this opened the way for much of modern [[science]] (and philosophy), which has the same goal of explaining the world without dependence on the supernatural.<ref>Lindberg, David C., ''The Beginnings of Western Science'' ([[University of Chicago Press]], 2010), pp. 28–9.</ref>

Thales of Miletus (7th to 6th century BC), the father of philosophy, claimed that the first principle of all things is water,<ref>[DK 7 B1a.]</ref> and considered it as a substance that contains in it motion and change. His theory was supported by the observation of moisture throughout the world and coincided with his theory that the Earth floated on water. His ideas were influenced by the Near-Eastern mythological cosmogony and probably by the [[Homeric]] statement that the surrounding [[Oceanus]] (ocean) is the source of all springs and rivers.<ref>{{cite book|title=The Pre-socratic Philosophers|author=G.S. Kirk, J.E. Raven and M. Schofield|year=2003|publisher=Cambridge University Press|isbn=9780521274555 |url=https://books.google.com/books?id=kFpd86J8PLsC}} p 89, 93, 94</ref>

Anaximander argued that water could not be the arche, because it could not give rise to its opposite, fire. Anaximander claimed that none of the [[Classical element|elements]] ([[earth]], [[fire]], [[air]], [[water]]) could be arche for the same reason. Instead, he proposed the existence of the [[Apeiron (cosmology)|apeiron]], an indefinite substance from which all things are born and to which all things will return.<ref>Simplicius, ''Comments on Aristotle's Physics'' (24, 13).[DK 12 A9, B1]</ref><ref>Curd, Patricia, ''A Presocratics Reader: Selected Fragments and Testimonia'' ([[Hackett Publishing]], 1996), pp. 9, 11 & 14.</ref> ''Apeiron'' (endless or boundless) is something completely indefinite; and Anaximander was probably influenced by the original ''chaos'' of Hesiod (yawning abyss).

Anaximander was the first philosopher that used ''arche'' for that which writers from Aristotle onwards called "the substratum" ([[Simplicius of Cilicia|Simplicius]] Phys. 150, 22).<ref>{{cite book|title=A History of Greek Philosophy|author=William Keith Chambers Guthrie|year=2000|publisher=Cambridge University Press|isbn=9780521294201 |url=https://books.google.com/books?id=ogUR3V9wbbIC }} p 55, 77</ref> He probably intended it to mean primarily "indefinite in kind" but assumed it also to be "of unlimited extent and duration".<ref>{{cite book|title=The Pre-socratic Philosophers|author=G.S.Kirk, J.E.Raven and M.Schofield|year=2003|publisher=Cambridge University Press|isbn=9780521274555 |url=https://books.google.com/books?id=kFpd86J8PLsC}} p 110</ref> The notion of temporal infinity was familiar to the Greek mind from remote antiquity in the religious conception of immortality and Anaximander's description was in terms appropriate to this conception. This ''arche'' is called "eternal and ageless". (Hippolitus I,6, I;DK B2)<ref>{{cite book|title=A History of Greek Philosophy|author=William Keith Chambers Guthrie|year=2000|publisher=Cambridge University Press|isbn=9780521294201 |url=https://books.google.com/books?id=ogUR3V9wbbIC}} p 83</ref>

Anaximenes, Anaximander's pupil, advanced yet another theory. He returns to the elemental theory, but this time posits air, rather than water, as the arche and ascribes to it divine attributes. He was the first recorded philosopher who provided a theory of change and supported it with observation. Using two contrary processes of [[rarefaction]] and [[condensation]] (thinning or thickening), he explains how air is part of a series of changes. Rarefied air becomes fire, condensed it becomes first wind, then cloud, water, earth, and stone in order.<ref>Daniel.W.Graham.  [http://www.iep.utm.edu/anaximen/ ''The internet Encyclopedia of Philosophy. Anaximenes''].</ref><ref>{{cite book|title=The Pre-socratic Philosophers|author=C.S.Kirk, J.E.Raven and M.Schofield|year=2003|publisher=Cambridge University Press|isbn=9780521274555 |url=https://books.google.com/books?id=kFpd86J8PLsC}} p 144</ref> The ''arche'' is technically what underlies all of reality/appearances.