X VOLITION: LIBERTY AND NECESSITY 217 



the stopping of any clock or watch, than to say that it does not 

 commonly go right. But an artist easily perceives that the same 

 force in the spring or pendulum has always the same influence 

 on the wheels ; but fails of its usual effect, perhaps by reason 

 of a grain of dust, which puts a stop to the whole movement. 

 From the observation of several parallel instances, philosophers 

 form a maxim, that the connexion between all causes and 

 effects is equally necessary, and that its seeming uncertainty in 

 some instances proceeds from the secret opposition of contrary 

 causes." (IV. pp. 101-2.) 



So with regard to human actions : 



" The internal principles and motives may operate in a uni- 

 form manner, notwithstanding these seeming irregularities ; in 

 the same manner as the winds, rains, clouds, and other varia- 

 tions of the weather are supposed to be governed by steady 

 principles ; though not easily discoverable by human sagacity 

 and inquiry." (IV. p. 103.) 



Meteorology, as a science, was not in existence 

 in Hume's time, or he would have left out the 

 "supposed to be." In practice, again, what dif- 

 ference does any one make between natural and 

 moral evidence ? 



" A prisoner who has neither money nor interest, discovers 

 the impossibility of his escape, as well, when he considers the 

 obstinacy of the goaler, as the walls and bars with which he is 

 surrounded ; and, in all attempts for his freedom, chooses 

 rather to work upon the stone and iron of the one, than upon 

 the inflexible nature of the other. The same prisoner, when 

 conducted to the scaffold, foresees his death as certainly from 

 the constancy and fidelity of his guards, as from the operation 

 of the axe or wheel. His mind runs along a certain train of 

 idoas : The refusal of the soldiers to consent to his escape ; the 

 action of the executioner ; the separation of the head and body ; 



