THE TWO ASPECTS OF SCIENCE 13 



briefly one other matter which belongs properly to this 

 preliminary stage. Are we right to speak at all of 

 " science " ? Every one knows to-day that there is not 

 one science but many. Physics, chemistry, astronomy, 

 geology, zoology, botany, physiology, psychology, and so 

 on, although all called " sciences," seem to be branches 

 of knowledge almost as separate as any science is from 

 philosophy. A chemist may be as ignorant of botany 

 as a philosopher of mathematics. Can we say anything 

 that is true of all these sciences and is not equally true 

 of mathematics or philosophy ? Well, that is one of the 

 questions that we have to answer, and our answer will 

 be affirmative ; we shall lay down a criterion which 

 appears to distinguish all sciences from any other branch 

 of pure learning. But a word may be said here about 

 the relations of the different sciences. 



The division between them corresponds in part to the 

 crude common-sense division of the external world of 

 nature. Thus we find some sciences (zoology, botany, 

 physiology) dealing with living beings and others (physics 

 and chemistry) with inanimate " matter." Further we 

 can distinguish sciences which deal with particular 

 objects from those which deal with the common sub- 

 stratum of objects. Thus geology deals with one parti- 

 cular object, the earth; and astronomy with other 

 particular objects, the stars ; zoology and botany 

 consider particular animals and plants. On the other 

 hand physics and chemistry deal with the substances 

 of which all particular material objects are composed ; 

 physiology with the functions common to all living 

 beings. So far the divisions between the sciences lie 

 along the lines that we should expect if science is the 

 study of the world of nature. But such divisions can 

 only be made very roughly. The province that is actually 

 regarded to-day as belonging to each science is very 

 largely the result of historical accident ; one line of 



