194 PHILOSOPHICAL THOUGHT. 



development of scientific thought during the century, 

 I followed an idea most clearly expressed by Herbert 

 Spencer, according to which science is partially unified 

 thought. There I took up those ideas and aspects 

 under the guidance of which a partial unification of 

 our knowledge of natural things has become possible. 

 Now in treating of the development of philosophical 

 thought I select those further conceptions which have 

 been used to arrive at a more complete if not an 

 ultimate unification of thought. As has already been 

 stated in the introductory chapter to this section, these 

 further conceptions are not to be found by looking 

 around us and outside, but rather by looking inside, by 

 introspection. They have become crystallised in certain 

 terms or words familiar in all the languages of the 

 civilised world. 



3. The conceptions under which we found it convenient 



conceptions to arrange the historical development of scientific thought 



ancient and 



modern. were mostly known already to the ancients. Modern 

 times, notably the nineteenth century, have more clearly 

 defined them, increasing them indeed by one or two 

 additional ideas such as energy and the doctrine of 

 averages. If we now look at the general conceptions, 

 expressed in definite words, which have governed modern 

 philosophical thought, we are still more struck by the 

 fact that they are not of modern origin. Although the 

 philosophical vocabulary has in the course of the nine- 

 teenth century enormously increased, it cannot be said that 

 any novel central idea is to be met with. All that has 

 been done by the enrichment of philosophical language 

 has been to attain to a clearer definition and under- 



