GENERAL SUMMARY AND CONCLUDING REMARKS. 395 



much more efficient an instrument than the mind to which it 

 ministers, that its presence can only be explained as a pre- 

 paration for the higher efficiency of mental life as afterwards 

 exhibited b)' civilized man. Lastly, Professor De Quatrefages 

 contradicts both the En^^lish naturalists by vehemently insist- 

 ing that, so far as the jjowcrs of intellect are concerned, there 

 is a demonstrable identity of kind between animal intelli- 

 gence and human, whether in the savage or civilized condi- 

 tion : he argues that the distinction only arises in the domain 

 of morals and religion. So that, if our opinion on the issue 

 before us were to be in any way influenced by the voice of 

 authority, I might represent the judgments of these my most 

 representative opponents as mutually cancelling one another 

 — thus yielding a zero quantity as against the enormous and 

 self-consistent weight of authority on the other side. 



But, quitting all considerations of authority, I proceeded 

 to investigate the question de novo, or exclusively on its own 

 merits. To do this it was necessary to begin with a some- 

 what tedious analysis of ideation. The general result was to 

 yield the following as my classification of ideas. 



1. Mere memories of perceptions, or the abiding mental 

 images of past sensuous impressions. These are the ideas 

 which, in the terminology of Locke, we may designate Simple, 

 Particular, or Concrete. Nowadays no one questions that 

 such ideas are common to animals and men. 



2. A higher class of ideas, which by universal consent 

 are also common to animals and men ; namely, those which 

 Locke called Complex, Compound, or Mixed. These arc 

 something more than the simple memories of particular per- 

 ceptions ; they are generated by the mi.xture of such memories, 

 and therefore represent a compound, of which " particular 

 ideas " are the elements or ingredients. By the laws of asso- 

 ciation, particular ideas which cither resemble one another in 

 themselves, or frequently occur together in experience, tend 

 to coalesce and blend into one: as in a "composite photo- 

 graph " the sensitive plate is able to unite many more or less 

 similar images into a single picture, so the sensitive tablet of 



