FALLACIES OF CONFUSION. 507 



It is, indeed, not a matter of inference but of authentic history, tliat 

 Plato's doctrine of Ideas, and the Anstotelian doctrine (essentially the 

 same as the Platonic) of substantial forms and second substances, frrew 

 up in the precise way here pointed out ; from the supposed necessity 

 of findinc:, in thinc^s vvliich wore said to have the same, nature, or the 

 satne qualities, somethinrr which was the same in the very sense in which 

 a man is the same as himself All the idle speculations respectinir to 

 6v, TO ev, TO o^oiov, and similar abstractions, so common in the ancient 

 and in some modern schools of philosophy, sprung from the same 

 source. The Aristotelian logicians had, however, seen one case of the 

 ambiguity, and provided against it, with their peculiar ft^licity in the 

 invention of technical language, when they distingnished things which 

 diflered both specie and numero from those which dirtero<l numero 

 tantum, that is, which were exactly alike (in some particular resjKict at 

 least) but were distinct individuals. An extension of this distinction 

 to the two meanings of the word Same, namely, things which are the 

 same specie tantum, and a thing which is the same numero as well as 

 specie, would have prevented the confusion which has been a source of 

 so much darkness and such an abundance of positive error in the higher 

 philosophy. 



One of the most singular examples of the lengths to which a philos- 

 opher of eminence may be led away by an ambiguity of language, is 

 afforded by this very case. 1 refer to the famous argument by which 

 Bishop Berkeley flattered himself that he had for ever put an end to 

 " skepticism, atheism, and irreligion." It is briefly as follows. 1 

 thought of a thing yesterday ; I ceased to think of it ; I think of it again 

 to-day. I had, therefore, in my mind yesterday an idea of the object ; 

 I have also an idea of it to-day : this idea is evidently not another, but 

 the very same idea. Yet an intervening time elapsed in which I had 

 it not. Where was the idea during this interval 1 It must have been 

 somewhere; it did not cease to exist; otherwise the idea 1 had yester- 

 day could not be the sa?ne idea; no more than a man I see alive to-day 

 can be the same whom I saw yesterday, if the man has died in the 

 meanwhile. Now an idea cannot be conceived to exist anywhere 

 except in a mind ; and hence here must exist an Universal Mind, in 

 which all ideas have their permanent residence, during the intervals of 

 their conscious presence in our own minds. 



That Berkeley here confounded sameness numero with sameness 

 specie, that is, with exact resemblance, and assumed the former when 

 there was only the latter, hardly needs be more particularly pointed 

 out. He could never have brf)ached this strange tlieory if he had 

 understood, that when we say we have the same thought to-day which 

 we had yesterday, we do not mean the same individual thought, but a 

 thought exactly similar: as wo say that we have the same illness which 

 we had last year, meaning only the same sort of illness. 



In one remarkable instance the scientific world was divided into two 

 furiously hostile parties by an ambiguity of langtiage affecting a branch 

 of science which, more completely than most others, enjoys the advan- 

 tage of a precise and well-defined terminology. I nsfi^r to the famous 

 dispute respecting the vis viva, the history (tf which is given at large in 

 Professor Playfair's Dissertation. The question was whuthi^r tho. /"orce 

 of a moving body was proportional (its mass being given) to its velocity 

 simply, or to the square of its velocity : and the ambiguity was in the 



