44 SCIENCE AND THE HUMAN MIND 



quences of the theory when deduced. The theory 

 remained a doctrine, like the metaphysical systems 

 of our own day, dependent on the mental attitude 

 of its originator and his followers, and liable to be 

 upset and replaced from the foundations by the new 

 system of a rival philosopher. And this, indeed, is 

 what happened. 



The Greek atomists reasoned from the general 

 knowledge of their day in the light of the prevalent 

 metaphysical ideas. When matter is divided and 

 subdivided, do its properties remain unchanged ? 

 Is earth always earth, and water water, however far 

 the process of division be carried ? In other words, 

 are the properties of bodies ultimate facts of which 

 no further explanation can be given ? Or can we 

 represent them in terms of simpler conceptions, and 

 thus push the limits of ignorance one step further 

 back ? 



It is this attempt at a rational explanation which 

 gives to the atomic theory of the Greeks its importance 

 in the history of thought. According to the ideas 

 that preceded its birth, the qualities of substances 

 were thought to be of their essence ; the sweetness of 

 sugar, and the colour of leaves, were as much a reality, 

 not to be explained by reference to other facts, as the 

 sugar and leaves themselves. 



In contra-distinction to this view, which made all 

 further enquiry useless, Democritus taught : " Accord- 

 ing to convention there is a sweet and a bitter, a hot 

 and a cold, and according to convention there" is colour. 

 In truth there are atoms and a void." 



The atoms of Democritus were uncaused and 

 existent from eternity. They were many in size and 



