EXTENSION OF LAWS TO ADJACENT CASES. 



3^t 



opaque revolving body will alternately 

 produce day and night ; but since the 

 sun no longer does shine on such 

 a body, the derivative uniformity, 

 the succession of day and night on 

 the given planet, is no longer true. 

 Those derivative uniformities, there- 

 fore, which are not laws of causation, 

 are (except in the rare case of their 

 depending on one cause alone, not on 

 a combination of causes) always more 

 or less contingent on collocations ; 

 and are hence subject to the charac- 

 teristic infirmity of empirical laws, 

 that of being admissible only where 

 the collocations are known by expe- 

 rience to be such as are requisite for 

 the truth of the law, that is, only 

 within the conditions of time and place 

 confirmed by actual observation. 



§ 2. This principle, when stated in 

 general terms, seems clear and indis- 

 putable ; yet many of the ordinary 

 judgments of mankind, the propriety 

 of which is not questioned, have at 

 least the semblance of being incon- 

 sistent with it. On what grotmds, it 

 may be asked, do we expect that the 

 sun will rise to-morrow ? To-morrow 

 IS beyond the limits of time compre- 

 hended in our observations. They 

 have extended over some thousands 

 of years past, but they do not in- 

 clude the future. Yet we infer with 

 confidence that the sun will rise to- 

 morrow ; and nobody doubts that we 

 are entitled to do so. Let us con- 

 sider what is the warrant for this con- 

 fidence. 



In the example m question, we 

 know the causes on which the deri- 

 vative uniformity depends. They are, 

 the sun giving out light, the earth in 

 a state of rotation and intercepting 

 light. The induction which shows 

 these to be the real causes, and not 

 merely prior effects of a common 

 cause, being complete, the only cir- 

 cumstances which could defeat the 

 derivative law are such as would 

 destroy or counteract one or other 

 of the combined causes. While the 

 causes exist, and are not counter- 



acted, the effect will continue. If 

 they exist and are not counteracted 

 to-morrow, the sun will rise to- 

 morrow. 



Since the causes, namely, the sun 

 and the earth, the one in the state of 

 giving out light, the other in a state 

 of rotation, will exist until sojnething 

 destroys them, all depends on the 

 probabilities of their destruction, or 

 of their counteraction. We know by 

 observation (omitting the inferential 

 proofs of an existence for thousands 

 of ages anterior) that these pheno- 

 mena have continued for (say) five 

 thousand years. Within that time 

 there has existed no cause sufficient 

 to diminish them appreciably, nor 

 which has counteracted their effect in 

 any appreciable degree. The chance, 

 therefore, that the sun may not rise 

 to-morrow amounts to the chance 

 that some cause, which has not mani- 

 fested itself in the smallest degree 

 during five thousand years, will exist 

 to-morrow in such intensity as to 

 destroy the sun or the earth, the 

 sun's light or the earth's rotation, or 

 to produce an immense disturbance 

 in the effect resulting from those 

 causes. 



Now, if such a cause will exist to- 

 morrow, or at any future time, some 

 cause, proximate or remote, of that 

 cause must exist now, and must have 

 existed during the whole of the five 

 thousand years. If, therefore, the 

 sun do not rise to-morrow, it will be 

 because some cause has existed, the 

 effects of which, though during five 

 thousand years they have not amounted 

 to a perceptible quantity, will in one 

 day become overwhelming. Since 

 this cause has not been recognised 

 during such an interval of time by 

 observers stationed on our earth, it 

 must, if it be a single agent, be either 

 one whose effects develop themselves 

 gradually and very slowly, or one 

 which existed in regions beyond our 

 observation, and is now on the point 

 of arriving in our part of the universe. 

 Now all causes which we have expe- 

 rience of act according to laws in- 



