ON THE NOTION OF CAUSE 219 



earlier and later times is determinate except in so far as 

 other forces than gravitation or other bodies than those 

 in the solar system have to be taken into consideration. 

 But other forces, so far as science can discover, appear 

 to be equally regular, and equally capable of being 

 summed up in single causal laws. If the mechanical 

 account of matter were complete, the whole physical 

 history of the universe, past and future, could be inferred 

 from a sufficient number of data concerning an assigned 

 finite time, however short. 



In the mental world, the evidence for the universality 

 of causal laws is less complete than in the physical world. 

 Psychology cannot boast of any triumph comparable to 

 gravitational astronomy. Nevertheless, the evidence is 

 not very greatly less than in the physical world. The 

 crude and approximate causal laws from which science 

 starts are just as easy to discover in the mental sphere as 

 in the physical. In the world of sense, there are to begin 

 with the correlations of sight and touch and so on, and 

 the facts which lead us to connect various kinds of sen- 

 sations with eyes, ears, nose, tongue, etc. Then there 

 are such facts as that our body moves in answer to our 

 volitions. Exceptions exist, but are capable of being 

 explained as easily as the exceptions to the rule that un- 

 supported bodies in air fall. There is, in fact, just such 

 a degree of evidence for causal laws in psychology as will 

 warrant the psychologist in assuming them as a matter 

 of course, though not such a degree as will suffice to 

 remove all doubt from the mind of a sceptical inquirer. 

 It should be observed that causal laws in which the given 

 term is mental and the inferred term physical, or vice 

 versa , are at least as easy to discover as causal laws in 

 which both terms are mental. 



It will be noticed that, although we have spoken of 



