INTRODUCTION. 



.ved, without reaching at last a widest truth which can be merged 

 in no other, or derived from no other. And whoever contemplates 

 : the relation in which it stands to the truths of science in general, 



S c 



vr-^dll see that this truth, transcending demonstration, is the Persist- 

 tence of force." * * * 



" Such, then, is the foundation of any possible system of posi- 

 C live knowledge. Deeper than demonstration deeper even than 

 definite cognition deep as the very nature of mind, is the postu- 

 late at which we have arrived. Its authority transcends all others 

 JT 3 whatever ; for not only is it given in the constitution of our own 

 *> *j J consciousness, but it is impossible to imagine a consciousness so 

 constituted as not to give it. Thought, involving simply the estab- 

 lishment- of relations, may be readily conceived to go on while yet 

 *o these relations have not been organized into the abstracts we call 

 C space and time ; and so there is a conceivable kind of consciousness 

 which does not contain the truths commonly called d priori, in- 

 volved in the organization of these forms of relations. But thought 

 cannot be conceived to go on without some element between which 

 ^ its relations may be established ; and so there is no conceivable 

 v kind of consciousness which does not imply continued existence as 

 ^ ^ iv its datura. Consciousness without this or that particular form is 

 possible ; but consciousness without contents is impossible. 



" The sole truth which transcends experience by underlying it, is 

 thus the Persistence of force. This being the basis of experience, 

 must be the basis of any scientific organization of experiences. To 

 this an ultimate analysis brings us down ; and on this a rational 

 synthesis must be built up." 



To the question, What then is the value of experimental inves- 

 tigations upon the subject, if the truth sought cannot be estab- 

 lished by inductions from them ? Mr. Spencer replies : " They are 

 of value as disclosing the many particular implications which the 

 general truth does not specify ; they are of value as teaching us how 

 much of one mode of force is the equivalent of so much of another 

 mode ; they are of value as determining uncler what conditions each 



