EXTENSION OF LAWS TO ADJACENT CASES. 391 



been any thing but conclusive. That a cause which, in opposition to very 

 powerful causes, produced no perceptible effect during five thousand years, 

 should produce a very considerable one by the end of twenty thousand, has 

 nothing in it which is not in conformity with our experience of causes. 

 We know many agents, the effect of which in a short period does not 

 amount to a perceptible quantity, but by accumulating for a much longer 

 period becomes considerable. Besides, looking at the immense multitude 

 of the heavenly bodies, their vast distances, and the rapidity of the motion 

 of such of them as are known to move, it is a supposition not at all contra* 

 dictory to experience that some body may be in motion toward us, or we 

 toward it, within the limits of whose influence we have not come during 

 five thousand years, but which in twenty thousand more may be producing 

 effects upon us of the most extraordinary kind. Or the fact which is ca- 

 pable of preventing sunrise may be, not the cumulative effect of one cause, 

 but some new combination of causes ; and the chances favorable to that 

 combination, though they have not produced it once in five thousand years, 

 may produce it once in twenty thousand. So that the inductions which 

 authorize us to expect future events, grow weaker and weaker the further 

 we look into the future, and at length become inappreciable. 



We have considered the probabilities of the sun's rising to-morrow, as 

 derived from the real laws ; that is, from the laws of the causes on which 

 that uniformity is dependent. Let us now consider how the matter would 

 have stood if the uniformity had been known only as an empirical law ; if 

 we had not been aware that the sun's light and the earth's rotation (or the 

 sun's motion) were the causes on which the periodical occurrence of day- 

 light depends. We could have extended this empirical law to cases adja- 

 cent in time, though not to so great a distance of time as we can now. 

 Having evidence that the effects had remained unaltered and been punctu- 

 ally conjoined for five thousand years, we could infer that the unknown 

 causes on which the conjunction is dependent had existed undiminished and 

 uncounteracted during the same period. The same conclusions, therefore, 

 would follow as in the preceding case, except that we should only know 

 that during five thousand years nothing had occurred to defeat perceptibly 

 this particular effect ; while, when we know the causes, we have the addi- 

 tional assurance that during that interval no such change has been notice- 

 able in the causes themselves as by any degree of multiplication or length 

 of continuance could defeat the effect. 



To this must be added, that when we know the causes, we may be able 

 to judge whether there exists any known cause capable of counteracting 

 them, while as long as they are unknown, we can not be sure but that if we 

 did know them, we could predict their destruction from causes actually in 

 existence. A bed-ridden savage, Avho had never seen the cataract of Niag- 

 ara, but who lived within hearing of it, might imagine that the sound he 

 heard would endure forever ; but if he knew it to be the effect of a rush of 

 waters over a barrier of rock which is progressively wearing away, he would 

 know that within a number of ages which may be calculated it will be heard 

 no more. In proportion, therefore, to our ignorance of the causes on which 

 the empirical law depends, we can be less assured that it will continue to 

 hold good ; and the further we look into futurity, the less improbable is it 

 that some one of the causes, whose co-existence gives rise to the derivative 

 uniformity, may be destroyed or counteracted. With every prolongation 

 of time the chances multiply of such an event ; that is to say, its non-occur- 

 rence hitherto becomes a less guarantee of its not occurring within the 



