552 FALLACIES. 



mitted ; when the investigation takes its proper direction, that of causes, 

 and the result erroneously obtained purports to be a really causal law. 



The most vulgar form of this fallacy is that which is commonly called 

 post hoc, ergo propter hoe, or, cum hoc, ergo propter hoc. As when it was 

 inferred that England owed her industrial pre-eminence to her restrictions 

 on commerce ; as when the old school of financiers, and some speculative 

 writers, maintained that the national debt was one of the causes of nation- 

 al prosperity ; as when the excellence of the Church, of the Houses of 

 Lords and Commons, of the procedure of the law courts, etc., were infer- 

 red from the mere fact that the country had prospered under them. In 

 such cases as these, if it can be rendered probable by other evidence that 

 the supposed causes have some tendency to produce the effect ascribed to 

 them, the fact of its having been produced, though only in one instance, is 

 of some value as a verification by specific experience ; but in itself it goes 

 scarcely any way at all toward establishing such a tendency, since, admit- 

 ting the effect, a hundred other antecedents could show an equally strong 

 title of that kind to be considered as the cause. 



In 'these examples we see bad generalization a posteriori, or empiricism 

 properly so called; causation inferred from casual conjunction, without ei- 

 ther due elimination, or any presumption arising from known properties 

 of the supposed agent. But bad generalization a priori is fully as common ; 

 which is properly called false theory ; conclusions drawn, by way of deduc- 

 tion, from properties of some one agent which is known or supposed to be 

 present, all other co-existing agents being overlooked. As the former is 

 the error of sheer ignorance, so the latter is especially that of semi-instruct- 

 ed minds ; and is mainly committed in attempting to explain complicated 

 phenomena by a simpler theory than their nature admits of. As when one 

 school of physicians sought for the universal principle of all disease in 

 "lentor and morbid viscidity of the blood," and imputing most bodily 

 derangements tp mechanical obstructions, thought to cure them by me- 

 chanical remedies ;* while another, the chemical school, " acknowledged no 

 source of disease but the presence of some hostile acid or alkali, or some 

 deranged condition in the chemical composition of the fluid or solid parts," 

 and conceived, therefore, that " all remedies must act by producing chem- 

 ical changes in the body. We find Tournefort busily engaged in testing 

 every vegetable juice, in order to discover in it some traces of an acid or 

 alkaline ingredient, which might confer upon it medicinal activity. The 

 fatal errors into which such an hypothesis was liable to betray the practi- 

 tioner, received an awful illustration in the history of the memorable fever 

 that raged at Leyden in, the year 1699, and which consigned two-thirds of 

 the population of that city to an untimely grave ; an event which in a great 

 measure depended upon the Professor Sylvius de la Boe, who having just 

 embraced the chemical doctrines of Van Helmont, assigned the origin of 

 the distemper to a prevailing acid, and declared that its cure could alone 



* "Thus Fourcroy," says Dr. Paris, "explained the operation of mercury by its specific 

 gravity, and the advocates of this doctrine fav(jied the general introduction of the preparations 

 of iron, especially in scirrhus of the spleen or liver, upon the same hypothetical principle ; for, 

 say they, whatever is most forcible in removing the obstruction must be the most proper in- 

 strument of cure : such is steel, which, besides the attenuating power with whicli it is fur- 

 nished, has still a greater force in this case from the gravity of its particles, which, being sev- 

 en times specifically heavier than any vegetable, acts in proportion with a stronger impulse, 

 and therefore is a more powerful deobstruent. This may be taken as a specimen of the style 

 in which these mechanical physicians reasoned and practiced." — Pharmacologia, pp. 38, 39- 



