The first Greek philosophers of nature were Thales, Anaximander, his student Anaximenes (appr. 570 BC) and in turn the latter’s assumed students Anaxagoras (appr 500 – 428 BC) and Diogenes. They were the first to distance themselves thoroughly from mythological thinking and enter theoretical thinking. They started the tradition of trying to explain the universe and general phenomena. Their school of thought is called the Miletan School. Thales believed in one material first substance to everything else, Anaximander believed in the indinite, apeiron, as the primary substance and Anaximenes believed that air was the primary substance to everything in the cosmos. Fire had to be thin air, water was thickened air, from further thinkening earth emerged and finally that must have become stone. This must have been a gradual two way process, depending on dominance of cold or heat. Also the human soul was made of air, according to Anaximenes. Planet Earth must have come into existence the same fashion, as a flat round disk, floating on air currents encircling her. Anaximander, his teacher, assumed that the Earth had the shape of a barrel floating in space. Anaximenes proclaimed ‘like our soul, consisting of air, keeping us together, thus breath and air keeps the entire world in place’. Similar condensations of air should have led to the birth of the Sun and stars. These bodies’ fiery nature would be caused by the speed of their motion, according to Anaximenes. Planet Earth had to be centre of the cosmos, with the stars as its most remote objects. The Moon was Earth’s most proximate object, then came the Sun, then the other planets. The Sun would not turn around the Earth, she would disappear every night behind the horizon and return every morning to her usual point of rising. Anaximenes thought that the Moon itself casts no light but thanks its rays of light to the Sun.
Anaxagoras believed that everything is infinitely divisible and that even the smallest portion of matter contains some of each element. The differences in form result from different portions of the elements and their seemingly endless numbers of possible combinations. Unlike Democritus he apparently did not believe in smallest particles, atoms, that form a material. Both the big and the small are infinite. Anaxagoras believed that the mind is the supreme ordering principle, it is infinite and self-controlling, it is mixed with nothing and is itself by itself. Anaxagoras was the first philosopher to introduce an abstract philosophical concept: Nous. Nous is the thinking, omnipotent, but impersonal Spirit or Mind. Thanks to this mind a well-ordered cosmos arose from the original chaos. This Nous seems to have been a first mover that left the universe to its own devices after initial creation, in Anaxagoras’ view. In everything there is a share of everything, except mind, and mind is present in some things too. Everything is in everything, all qualities are present in even the smallest core and this enables a smooth transition from one material into another and makes birth and destruction of matter just false appearance. Living creatures possess, unlike dead creatures, Nous. This same Nous gives men and animals their soul. Men seems superior to animals, because he has hands. Visible differences in intellect are consequence of physical differences. Being an astronomer, Anaxagoras observed vortexes and spiral phenomena in nature and he believed that the universe was created through the rotary motion of a spiral, where initially all mass was united in the center and driven by a centrifugal force driven by ‘mind’, celestial bodies and other things came into being through seperation of mass. Today some say, that if the mass of a galaxy was concentrated at its center, it would have created a black hole and gravitation would be too strong for anything to escape from it. Stars and the Sun are fiery stones, but we can’t feel the heat because of their distance, according to Anaxagoras. He thought to recognize mountains and living creatures on the Moon and the Sun had to be bigger than the Peloponnesos. Anaxagoras proved that air was no vacuum but material substance by blowing up utters and a pipet that enclosed air by water and he concluded that sound had to be movement of air. Anaxagoras was highly respected in Athens, not in the least by statesman Pericles, but later he was accused of Persian sympathies and heresy when he taught that the Sun was a fiery stone and the Moon only earth. He had to leave Athens, in spite of Pericles’ protection, and return to Ionia.
Diogenes, who was a doctor, believed as well that air was the source of all Being from which all substances can be produced; the only difference between air and other Beings is its thickness. Diogenes, however, accredited air, as the first matter, intelligence. ‘The air swirling within him not only supported, but directed also. Air as source of all things is necessary as perpetual and indestructible matter, but as a soul it is also equipped with a conscience’. Diogenes also believed in an indefinite number of worlds and supported the idea that the Earth is a round ball supported by air. Diogenes, however, did not follow Anaxagoras’ dualism. Diogenes probably had atheist sympathies, which may have cost him popularity in Athens.
Fragments and quotes of the ancient philosophers’ works, no more, have been preserved and quoted by later authors, such as passages from Diogenes’ most important work ‘De natura’. Other works from his hand are possibly ‘Against the sophists’, ‘Against the philosophists of nature’, ‘On Meteorology’ and ‘On the nature of man’. Anaxagoras has written one book, of which quotes have been preserved by Simplicius. Pythagoras left us no writings. Marcus Tullius Cicero (106 – 43 BC) was the first author to use the name ‘Presocratic’ philosophy for the ancient Greek philosophers before Socrates. Orpheus lyrics have been preserved, however, Aristotle denied their originality. Diogenes Laertius, 3rd Cent AD, wrote an extended biography on Greek philosophers. The work of these philosophers, however, meant a turning point from mythical and traditional religious thinking towards theoretical thinking and observation, even though many philosophers suffered disapproval to downright persecution in Athens. Not just devine explanations behind the univers were narrated and taught, from now on thought was given to processes and characteristics in nature and man themselves.
And thus we arrive at a man who was among the first to introduce religious skepticism and gained unrivaled status in philosophy when sophism was at its height of popularity: Socrates.