368 INDUCTION. 



causa materialis. The next condition is, there must be an 

 earth : and accordingly it is often said, that the fall of a stone 

 is caused by the earth ; or by a power or property of the 

 earth, or a force exerted by the earth, all of which are merely 

 roundabout ways of saying that it is caused by the earth ; 

 or, lastly, the earth's attraction ; which also is only a technical 

 mode of saying that the earth causes the motion, with the 

 additional particularity that the motion is towards the earth, 

 which is not a character of the cause, but of the effect. Let 

 us now pass to another condition. It is not enough that the 

 earth should exist ; the body must be within that distance 

 from it, in which the earth's attraction preponderates over 

 that of any other body. Accordingly we may say, and the 

 expression would be confessedly correct, that the cause of the 

 stone's falling is its being within the sphere of the earth's 

 attraction. We proceed to a further condition. The stone is 

 immersed in water : it is therefore a condition of its reaching 

 the ground, that its specific gravity exceed that of the sur- 

 rounding fluid, or in other words that it surpass in weight 

 an equal volume of water. Accordingly any one would be 

 acknowledged to speak correctly who said, that the cause of 

 the stone's going to the bottom is its exceeding in specific 

 gravity the fluid in which it is immersed. 



Thus we see that each and every condition of the pheno- 

 menon may be taken in its turn, and, with equal propriety in 

 common parlance, but with equal impropriety in scientific dis- 

 course, may be spoken of as if it were the entire cause. And 

 in practice, that particular condition is usually styled the cause, 

 whose share in the matter is superficially the most conspi- 

 cuous, or whose requisiteness to the production of the effect 

 we happen to be insisting on at the moment. So great is the 

 force of this last consideration, that it sometimes induces us 

 to give the name of cause even to one of the negative condi- 

 tions. We say, for example, The army was surprised because 

 the sentinel was off his post. But since the sentinel's absence 

 was not what created the enemy, or put the soldiers asleep, 

 how did it cause them to be surprised ? All that is really 

 meant is, that the event would not have happened if he had 



