iv MODERN SCIENCE 



349 



first. Wherein consists the difference of attitude of 

 the two sciences toward change ? We may formu 

 late it by saying that ancient science thinks it knows its 

 object sufficiently when it has noted of it some privileged 

 moment s, whereas modern science considers the object at 

 any moment whatever. 



The forms or ideas of Plato or of Aristotle corre 

 spond to privileged or salient moments in the history 

 of things those, in general, that have been fixed by 

 language. They are supposed, like the childhood or 

 the old age of a living being, to characterize a period 

 of which they express the quintessence, all the rest 

 of this period being filled by the passage, of no interest 

 in itself, from one form to another form. Take, for 

 instance, a falling body. It was thought that we got 

 near enough to the fact when we characterized it as a 

 whole : it was a movement downward ; it was the 

 tendency toward a centre ; it was the natural movement 

 of a body which, separated from the earth to which it 

 belonged, was now going to find its place again. 

 They noted, then, the final term or culminating point 

 (reXo?, a/cyu,??) and set it up as the essential moment : 

 this moment, that language has retained in order 



* O O 



to express the whole of the fact, sufficed also for 

 science to characterize it. In the physics of Aristotle, 

 it is by the concepts &quot;high&quot; and &quot;low,&quot; spontaneous 

 displacement and forced displacement, own place and 

 strange place, that the movement of a body shot into 

 space or falling freely is defined. But Galileo thought 

 there was no essential moment, no privileged instant. 

 To study the falling body is to consider it at it matters 

 not what moment in its course. The true science of 

 gravity is that which will determine, for any moment 

 of time whatever, the position of the body in space. 



