FALLACIES OF RATIOCINATION. 435 



scarcely ever possible decidedly to affirm that any 

 argument involves a bad syllogism : but this detracts 

 nothing from the value of the syllogistic rules, since 

 it is by them that a reasoner is compelled distinctly 

 to make his election what premisses he is prepared 

 to maintain. The election made, there is generally 

 so little difficulty in seeing whether the conclusion 

 follows from the premisses set out, that we might 

 without much logical impropriety have merged this 

 fourth class of fallacies in the fifth, or Fallacies of 

 Confusion. 



4. Perhaps, however, the commonest, and cer- 

 tainly the most dangerous fallacies of this class, are 

 those which do not lie in a single syllogism, but slip 

 in between one syllogism and another in a chain of 

 argument, and are committed by changing the pre- 

 misses. A proposition is proved, or an acknowledged 

 truth laid down, in the first part of an argumentation, 

 and in the second a further argument is founded not 

 upon the same proposition, but upon some other, 

 resembling it sufficiently to be mistaken for it. In- 

 stances of this fallacy will be found in almost all the 

 argumentative discourses of unprecise thinkers; and 

 we need only here advert to one of the obscurer forms 

 of it, recognised by the schoolmen as the fallacy a 

 dicto secundum quid ad dictum simpliciter. This is com- 

 mitted when, in the premisses, a proposition is asserted 

 with a qualification, and the qualification lost sight 

 of in the conclusion; or oftener, when a limitation or 

 condition, though not asserted, is necessary to the truth 

 of the proposition, but is forgotten when that propo- 

 sition comes to be employed as a premiss. Many of the 

 bad arguments in vogue belong to this class of error. 

 The premiss is some admitted truth, some common 



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