238 



Thoughts on Causality. 



sary truths and admitted principles, is a permissible and 

 safe procedure, and so natural and available, that, not unfre- 

 quently, the scientist himself falls into the use of it, at the 

 same time that he professes to observe rigorously the 

 canons of scientific induction. 



The test of a physical truth, that it must be capable of 

 mental presentation, is legitimate ; but a moment's reflec- 

 tion will convince any one that it is an impossible test in 

 the whole field of abstract ideas. By what sort of process, 

 for instance, would Professor Tyndall bring before his 

 mind's eye a vorstellung of cheapness, or ambition, or de- 

 spair, or even the generalization induced from a body of 

 phenomena? 



In this phenomenal world, science disposes its data accord- 

 ing to their resemblances, concomitances and sequences. 

 An observed invariable sequence is styled a law. In the 

 generalized faith that a certain sequence will remain invari- 

 able, science forecasts terms which lie in the future ; and, 

 in a similar faith that it has always been invariable, science 

 retraces the pathway of phenomena into the inaccessible 

 past. But it is of the utmost importance to refrain from 

 endowing the word law with the notion of efficiency. We 

 say loosely that the law of chemical affinities causes the 

 disengagement of carbonic acid when chalk and sulphuric 

 acid are brought together ; that it is a law of life that the 

 stomach should not be dissolved by its own juices ; that it 

 is the law of the " survival of the fittest" which causes the 

 progressive improvement either assumed or proven in the 

 successive generations of a species in the state of nature. 

 We are apt to think that when we have ranged a phe- 

 nomenon under its appropriate order of sequence, we have 

 pointed out its cause ; whereas, laws are only uniformities 

 of juxtaposition of phenomena. There is no efficacy inlaw. 

 It is not a force, but only the method of activity of force 

 or the order of its effects. The law which expresses the 

 relations subsisting between the intensity of gravity and 



