In the absence of written documents, it is difficult to explain this radical change, which one sometimes describes as “Greek miracle”. Perhaps the regrouping of various local cultures in the same expansionist hegemony creates it a need for political stability and obliges it to invent a new speech of conciliation, where the analysis of the phenomena occupies a great place. In parallel, the appearance of new worships, more individualistic, could weaken the influence which exerted on the spirits traditional mythology.  
 
Greek science

Science as a search for a rational explanation to the natural phenomena thus starts with the Greeks. The concept even of science épistémê is a Greek invention; it indicates a coherent way to give an account of the physical world starting from a small number of assumptions metaphysics, from which rise logically from the proposals allowing to explain the observable phenomena. Thanks to science, the Greeks will raise the technical training which they inherited on a level of abstraction never yet reached.

Greek science was not born from nothing. By their contacts with civilizations Mesopotamian and Egyptian, the Greeks discover mathematics, astronomy, medicine and the techniques such that these cultures practice them, but this corpus of knowledge, which will occupy a paramount place in the Greek thought of the Life and Ve century, plays a not very important part, even non-existent, in the first attempts to apprehend the physical world rationally.

The first Greek “physicists” indeed apply their faculties of analysis to the phenomena most immediately observable; thus, at the beginning of the VI E century - in particular in Ionie - three fundamental questions arise:  

- Which is the reality fundamental, single, which underlie and unify the apparent diversity of nature, or, to take again their own term, which is the phusis?  

- How diversity born is from this fundamental unit?  

- Which is the source and does movement (or change) cause in the world?  
 
“Physicists” and philosophers

The answers brought to these paramount questions vary according to the thinkers, but they are divided into two main categories which one respectively describes as “materialism” and of “formalism”.  The first philosophers, the “physicists” of Ionie, transpose, to the VI E century, of old mythical cosmogonies.  

Thalès de Milet, at the beginning of the VI E century, proposes a material phusis: the principle first is water, because it is presented naturally in three states of the matter (gas, liquid and solid) and that the richness of the sea life seems to make of it the source of all the life. For the remainder, nothing Thalès is known, but one of its pupils, Anaximandre, further pushes the abstraction while explaining than if the phusis is material, it must be an undifferentiated matter, from where then the diversity of the objects of the sensitive world emerges.  

But all the materialists do not accept the idea of a single phusis. The nuclear physicists, of which most known is undoubtedly Démocrite d' Abdère, at the end of the O C century, postulate the existence of tiny material particles moving in an empty space. The multiple shapes and combinations of the particles explain the variety of nature, and their constant recombinations are the cause of the changes which one observes in the universe. For certain nuclear physicists, the number of the particles is infinite; for others, it important but is finished. The Empédocle philosopher, with the O C century, imagines a world made up of four basic elements (ground, water, air and fire) in variable proportions.

The formal ones - and in particular disciples of Pythagore, to the VI E century - accept the material world like a preexistent data, of which it is advisable to seek the principles of organization rather. For them, the world is an ordered, harmonious, balanced cosmos and organics which owes its order and its form with the numbers and their properties. The pythagorism is, as much as a science, a religion with strong mystical component, but it bequeaths to the posterity what will become the instrument of privileged research and the mode of expression of rational sciences: mathematics.

Cosmos

It offers the aspects different from same a phusis (“natural”), and from a principle first (water for Thalès de Milet, the infinite one for Anaximandre, air for Anaximène) the generation depends on all that saw. In Occident, the Pythagorean ones rather seek in the numerical reports this gasoline of the things, and Xénophane de Colophon, which was to have a decisive influence, with the O C century, on the school éléate (Parménide and later Zénon), replace the number by one, motionless and immutable, and in parallel affirm the incompatibility of the human reason with the anthropomorphic beliefs of the religion.  

The Life century is also the age where, with logographes like Hécatée de Milet, create for themselves the history and geography that Ve century, there still, will develop with Hérodote and especially Thucydide, our essential sources on the history of the contemporary Greek world (Xénophon, its continuator, is far from having its qualities of analysis). It is the time also where, in Greece of Asia, a first medical school based on the observation develops, that of Hippocrates, which competes with the school of Cnide, more traditional, whereas in Occident that of Crotona, with Alcméon, seems to nourish Pythagorean reflections.  

As for Empédocle d' Agrigente, it tries to solve contradiction between the appearance of the multiple things and the unit Être. Its theory of the elements, used by Aristote, was to continue until the Middle Ages. Alchemy and homeopathy will remember later its doctrines according to which “the similar one knows the similar one”.  
 

These présocratiques testifies to the glare of the civilization which accompanies maturity by the archaism. Scientists as much as philosophers, they open the era of a multiple research, guided by the reason.  

It is with Socrate, and after him, with Plato and Aristote, that philosophy separates from science and fact from the man, more than of the world, the main object of its reflections.

Plato and Aristote

Are the two large currents of presocratic philosophy found in the thoughts of Plato (427? - 347? front J. - C.) and of Aristote (384-322 av. J. - C.), which diverge on the question from nature from our knowledge from the physical world. On several occasions, in particular in Timée, Plato supports that, insofar as we apprehend the world by the means of our directions, nothing proves that knowledge that we have some is not illusory, because the directions can mislead the spirit. At best, the man can hope to give world a “explanation probable”, that Plato presents in Timée in the form of a “myth” where universe, basically Pythagorean, is composed of a matter organized in harmonious proportions.  

Cosmogony and cosmology eclectics of Plato will have an influence limited on the scientific thought. However, the mathematical dimension of Timée, and the place which mathematics in Platonic epistemology and pedagogy occupies elsewhere, reinforce the importance already given by Pythagore to mathematics as a key of the knowledge of the physical world.  

If Plato is wary of the directions, Aristote sees there on the contrary the source of any knowledge. The world which one sees and which one feels is the only accessible one, and our ideas come from the abstractions which we operate on this sensory experiment. From this central conviction, Aristote works out a theory of the scientific knowledge and a corpus of positive sciences which will dominate physics and biology Western to the XVII E century, and which, even afterwards, will continue to exert a certain influence.  

In the scientific discipline, Aristote is interested in particular in biology. Its theory of sciences, moreover, expresses a vision taxonomist of the universe: the world is composed individuals whom the scientist learns how to know by determining the features which distinguish them and those that they divide with others. These shared properties define classes, which all the more understand individuals that the properties of these classes are general. For example, each man has attributes which differentiate it from the other men, but all the men in common have a property which characterizes the Man in a single and essential way. While extending this process of abstraction, the man enters broader classes: that of the animals, then that of the living beings. Each time, the scientist must carefully examine which common properties characterize in a way single and essential the individuals who compose the studied class.  

The objective of the scientist is thus to define a hierarchical classification of nature and, from there, to arrive by induction at the most general possible assertions, i.e. with the principles first. Aristote answers the three questions mentioned above thus: as regards the phusis, he thinks that the sensitive world and the objects which compose it come from a material substrate differentiated and individualized by various properties. Neither the substrate nor the forms can exist separately, and it is of this answer to the problem of the phusis that rises the fundamental concern from Aristote for the classification of the forms.

The theory of the movement at Aristote

What distinguishes the theory of Aristote of those of its predecessors is less the answer than it brings to the first two questions than the clever solution than it gives to the problem of the movement. By movement, Aristote hears the quantitative change (growth), qualitative (for example, color) or room (movement itself). Change, it notes, can occur only in the accidental properties of an object, i.e. the properties which are not used to characterize it in its gasoline.  

The physical existence is characterized itself by a constant change, and “physics” (study of nature in general) is a motion study. To understand the movement, Aristote wants to thus know of them the causes, which are four. Taking the example of a bronze statue, he explains why bronze becomes a statue because:  
 1. it is malleable and can be worked (causes material);  
 2. a sculptor makes a statue of it (causes efficient);  
 3. a sculptor has a model from which he works (causes formal);  
 4. the sculptor wants to make a statue (causes final).  

Also the Aristotelian scientist must it not only classify the phenomena of the physical world but also give an account of the methods and the causes of their changes.  

The efficient and final causes will take an particular importance in the later evolution of the Aristotelian theory. Aristote indeed establishes a fundamental distinction between the natural change and the “violent” change. In the first, the efficient cause is nature, or the gasoline of the object itself. For example, the men grow naturally, and it is also in the nature of the man, as an animal, to be able to change place. The stones, on the other hand, move naturally only in only one direction: they fall downwards. A stone which moves in another direction thus supposes an agent, i.e. an external efficient cause which should be determined. To find the cause efficient of the movement of a stone as from the moment when this one leaves the hand of that which it lance will be one of the major problems that the disciples of Aristote will be posed, in particular at the end of the Middle Ages. The research of the answer to this question will open the way, to the XVII E century, dynamics.  
 
Teleological approach

The investigation into the final cause - most important according to Aristote - characterizes well the teleological step of Aristotelian science, because any movement, and, in fact, all that exists in the physical world, has a goal towards which it tends. The central objective of the scientist is to determine in each case which is this goal. This idea of the importance of the final causes - that Aristote divides with other Greek thinkers but that its philosophical system particularly will contribute to spread - explains many Greek scientific concepts, for example concerning the finished character of the universe or the impossibility of the vacuum.  

This teleological approach also explains the tendency of the Greeks to analyze and describe the physical world in human terms. Thus, they judge nature with criteria generally considered today as eminently subjective, such as the harmony or kindness. Reciprocally, nature is a source of values morals, because Greek science also seeks, basically, to define the harmony which links the man with nature.