Within ancient Greek pre-Socratic philosophy there were two major branches dealing with the questions of change. At one extreme, there was Zeno of Elea with his famous paradox who tried to show that the universe was constant and changeless. At the other extreme, there is Heraclitus with the famous quote "You cannot step twice into the same river".

The notion of basic change and movement comes from Anaximander (about 600 BC) with the proposition that the universe initially was an infinite, whole mass. The concept of 'whole' means 'not broken into pieces'. However, this mass had motion, and as it moved pieces broke off from this mass and eventually came to be the universe as we know it. As the motion continues these pieces will eventually be brought back together and the "infinite" will assume its original unbroken unity. He also wrote detailed accounts about how all that we see was created from these pieces of the original infinite.

As ancient philosophers worked with the questions of the origins of the universe, they realized that change was a considerable issue - how the universe got from there to here. Do things really change or are we just imagining it?

Heraclitus took the stand that the universe was in constant flux and that fire was the original stuff of the universe. Fire, as we see it, is constantly changing and flickering. With fire one substance is transformed into another. From this came the Greek: Potauoisi dis toisi autoisi ouk an embaies etera gar <kai etera> epirreei udata which translates to "The river where you set your foot just now is gone - those waters giving way to this, now this." (the full version of "You cannot step twice into the same river"). The essence of this teaching is that there is nothing that is permanent or stable - change is the only constant. When we think that we see something that doesn't change, we are deceived. If we had eyes powerful enough to see what was happening, we would realize that even the most stable thing in the universe is in a constant state of flux. Once something is created, it begins to change.

At about the same time as Heraclitus was the philosophers of Elea were teaching that change in the universe was impossible. Of these philosophers (known as the Eleatics), the earliest was Xenophanes who posed that the universe was an unchangeable solid mass - while pieces might change, the whole never would. Parmenides tried to show that change was a logical impossibly and thus inconceivable. If there was change, something would have to come from nothing which was 'impossible'. That which we see as 'change' is an illusion. Zeno went a step further with the example of Achilles and the tortoise to show that any attempt to prove the existence of change is a contradiction itself.

This riddle of permanence and change drew some attention in the ancient Greek world and there were some different approaches to reconciling the two different schools.

Empedocles agreed with the Eleatic school that in the strict sense there is no change. However, he also agreed with Heraclitus that there was a general "mingling and separation" within the universe. The universe itself is composed of four elements: earth, air, fire and water. There are millions of particles for each element and these combine in different ways to form all that we see. As things decay and change, these elements separate. The composition of the particles, however, never changes. The mingling and separation of particles was caused by Love (bringing them together) and Hate (breaking them apart).

Anaxagoras, while intrigued by Empedocles' solution found it did not satisfy him. After careful study, Anaxagoras concluded that there were many more than four elements. The different types of elements ranged in the millions of substances. Our flesh and bones were the result of millions of different flesh and bone particles combing as was everything else in the universe. No element can be changed into another and thus there was fundamentally no change and yet as the elements combined, separated and recombined there was change. These motions were not from any force within them (such as Love or Hate), but rather the motions of the universe.

This lead the way for the school of Greek philosophy known as the Atomists. Most famous of these schools are Leucippus and Democritus. While they both agreed with their predecessors that change was the result of combining and separation of atoms, they disagreed about the nature of the elements. Prior to the Atomists, the belief was that elements differed in quality; that is that flesh elements where different from bone elements. The Atomists taught that all units (called 'atoms') where alike in quality with hooks, holes, bumps and grooves and other such ways of connecting. Within each atom, there is also motion so that it moves about and attaches itself to other atoms.

The essence of change for the Atomists was then a matter of separating and combining atoms. These atoms were never changed but constant, very small, and identical (thus there was no change from one type to another). The things we see in the world are then different arrangements of groups of atoms.

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