542 FALLACIES. 



their preconceived impressions, we need not be surprised that this should 

 be so lamentably true as all experience attests it to be, on things more 

 neai'ly connected with their stronger feelings — on moral, social, and i-elig- 

 ious subjects. The information which an ordinary traveler brings back 

 from a foreign country, as the result of the evidence of his senses, is almost 

 always such as exactly confirms the opinions with which he set out. He 

 has had eyes and ears for such things only as he expected to see. Men read 

 the sacred books of their religion, and pass unobserved therein multitudes 

 of things utterly irreconcilable with even their own notions of moral ex- 

 cellence. With the same authorities before them, different historians, alike 

 innocent of intentional misrepresentation, see only what is favorable to 

 Protestants or Catholics, royalists or republicans, Charles I. or Cromwell ; 

 while others, having set out with the preconception that extremes must 

 be in the wrong, are incapable of seeing truth and justice when these are 

 wholly on one side. 



The influence of a preconceived theory is well exemplified in the super- 

 stitions of barbarians respecting the virtues of medicaments and charms. 

 The negroes, among whom coral, as of old among ourselves, is worn as an 

 amulet, aftirm, according to Dr. Paris,* that its color " is always affected 

 by the state of health of the wearer, it becoming paler in disease." On a 

 matter open to imiversal observation, a general proposition which has not 

 the smallest vestige of truth is received as a result of experience ; the pre- 

 conceived opinion preventing, it would seem, any observation whatever on 

 the subject. . 



§ 4. For illustration of the first species of non-observation, that of In- 

 stances, what has now been stated tnay suffice. But there may also be 

 non-observation of some material circumstances, in instances which have 

 not been altogether overlooked — nay, which may be the very instances on 

 which the whole superstructure of a theory has been founded. As, in the 

 cases hitherto examined, a general proposition was too rashly adopted, on 

 the evidence of particulars, true indeed, but insufficient to support it; so 

 in the cases to which we now turn, the particulars themselves have been 

 imperfectly observed, and the singular propositions on which the generali- 

 zation is grounded, or some at least of those singular propositions, are 

 false. 



Such, for instance, was one of the mistakes committed in the celebrated 

 phlogistic theory ; a doctrine which accounted for combustion by the ex- 

 trication of a substance called phlogiston, supposed to be contained in all 

 combustible matter. The hypothesis accorded tolerably well with super- 

 ficial appearances ; the ascent of flame naturally suggests the escape of a 

 substance; and the visible residuum of ashes, in bulk and weight, generally 

 falls extremely short of the combustible material. The error was, non-ob- 

 servation of an important portion of the actual residue, namely, the gaseous 

 products of combustion. When these were at last noticed and brought 

 into account, it appeared to be a universal law, that all substances gain in- 

 stead of losing weight by undergoing combustion ; and after the usual at- 

 tempt to accommodate the old theory to the new fact by means of an ar- 

 bitrary hypothesis (that phlogiston had the quality of positive levity in- 

 stead of gravity), chemists were conducted to the true explanation, namely, 

 that instead of a substance separated, there was, on the contrary, a substance 

 absorbed. 



* Pharmacologia, p. 21. 



