One of the most important achievements of ancient Greek thought of the 5th century BC was undoubtedly the genesis of the concept of the atom, this tiny amount of matter that has occupied scientists and philosophers for thousands of years.
The important current that first conceived this idea was the atomic philosophy. Its representatives studied with the "Dorian" Eleatan philosophers but also opposed them. They therefore accepted the doctrine of their teachers that "BEING" is unborn and incorruptible but at the same time claimed that it moves and is divided.
Atomic philosophers first acknowledged the coexistence of emptiness and non-emptiness in the universe. The existence of a vacuum is a necessary condition for the possibility of division of physical bodies. However, they rejected the view of Zeno the Eleat about the infinite division of bodies. That is, they supported the existence of finite molecules of matter, which can not be further cut and remain atoms. Thus the theory of the atom was conceived.
The most important atomic philosopher was Democritus (470/460 - 400/390 BC) from Abdera in Thrace, the most versatile and methodical mind before Aristotle. He dealt with issues of physics, epistemology, human behavior, social and political organization.
Democritus defined the atom as unborn, incorruptible, unchangeable, complete and perfect, uniformly compact, free from emptiness, simple, unified and amorphous, without fluctuations, dilutions and densities or expansions and contractions, indivisible and with definite boundaries. In his opinion, atoms were infinite in number and shapes and moved eternally into space.
An important difference between the theory of Democritus and that of the Eleats was that the former meant substance not metaphysically but materially. At the same time, he considered the phenomena of nature not as an illusion of people but as something that happens around the essence.
As for how a world is created, Democritus taught that it is composed when in a large space void many atoms collide with each other to form a vortex. In the vortex, similar atoms are attracted to each other and form known physical bodies such as fire, water, air and earth. Then the heavier materials gather in the center and create the earth while the lighter ones are pushed towards the periphery creating the celestial bodies and the meteorological phenomena. Thus infinite worlds are synthesized and decomposed. In fact, he defined as their way of destruction the fall of one world over another. Finally, he argued that in some worlds there is no sun and moon while in others there are many such celestial bodies. In addition, the philosopher believed that in many worlds there are no liquids, animals and plants.
Democritus also formulated positions in the field of biology. Thus he argued that the skills and organs of the various animals were created by chance and that only those organs that seemed necessary to preserve each species were saved. The philosopher also considered every living organism as a small world.
As for the soul, Democritus considered it as a physical body, with a composition like fire, he identified it with the mind and believed that it wears together with the body.
For knowledge, the philosopher taught that it is related to the situations that surround each person and that the truth is at the bottom, that is, in the void and in atoms. The process of knowledge was for him a natural mechanism, which in fact was based on the "dark" sense and the "genuine" intellect. For the second to exist, a necessary condition was the existence of the first, as Aristotle later believed.
Finally, a characteristic formulation of the philosopher about the importance of teaching was this: "Teaching is close to nature because it restructures human nature and thus creates a new nature."
Today, about 300 excerpts from numerous books by Democritus survive.
