FALLACIES OF TESTIMONY. 573 



to all which concerns the " supernatural " (using that term in its gen- 

 erally understood sense, without attempting a logical definition of it), 

 the allowance that has to be made for " prepossession " is so large as 

 practically to destroy the validity of any testimony which is not sub- 

 mitted to the severest scrutiny according to the strictest scientific 

 methods. Of the manner in which, within my own experience, wliat 

 seemed the most trustworthy testimony has been completely discred- 

 ited by the application of such methods, I shall give some examples 

 hereafter. 



I would by no means claim for myself or any other scientific man 

 an immunity from idoln.trous prepossessions; for we must all be guided 

 in our researches by S07ne notion of what we expect to find ; and this 

 notion may be very misleading. Thus, when no metal was known 

 that is not several times heavier than water, it was not surprising that 

 Dr. Pearson, as he poised upon his finger the first globule of potassium 

 produced by the battery of Davy, should have exclaimed, " Bless me, 

 how heavy it is ! " though, when thrown into water, the metal floated 

 upon it. But while the true disciple of Bacon is on his guard against 

 " idolatry," and is constantly finding himself inidely handled (as Dr. 

 Pearson was) by "the irresistible logic of facts" if he falls into it, the 

 pledged upholder of any religious system can be scarcely other than, 

 in some degree, an " idolater." The real philosopher, says Schiller, is 

 distinguished from the " trader in knowledge " by his " always loving 

 truth better than his system." 



Bacon's classification of " idols " is based on the sources of our pre- 

 possessions; and, although his four types graduate insensibly into 

 each other, yet the study of them is very profitable. Sir John Her- 

 schel is, I think, less successful when he classifies them as 1. Preju- 

 dices of opinion, and 2. Prejudices of sense ; because an analysis of 

 any of his " prejudices of sense " shows that it is really a " prejudice of 

 opinion." My first object is to show that we are liable to be afiected 

 by our prepossessions at every stage of our mental activity, from our 

 primary reception of impressions from without, to the highest exer- 

 cise of our reasoning powers ; and that the value of the testimony 

 of any individual, therefore, as to any fact whatever, essentially 

 depends upon his freedom from any prepossessions that can afiect it. 



That our own states of consciousness constitute what are, to each 

 individual, the most certain of all truths in a philosophical sense (as 

 J. S. Mill says) the only certain truths will, I suppose, be generally 

 admitted ; but there is a wide hiatus between this and the position 

 that eveiy state of consciousness which represents an external object 

 has a real object answering to it. In fact, although w^e are acccus- 

 tomed to speak of " the evidence of our senses " as worthy of the high- 

 est credit, nothing is easier than to show that the evidence of any one 

 sense, without the check afforded by comparison with that of another, 

 is utterly untrustworthy. 



