FALLACIES OF RATIOCINATION. 379 



to compel it to do so is the most effectual method of detecting 

 and exposing it. 



3. Among Fallacies of [Ratiocination are to be ranked 

 in the first place, all the cases of vicious syllogism laid down 

 in the books. These generally resolve themselves into having 

 more than three terms to the syllogism, either avowedly, or in 

 the covert mode of an undistributed middleterm, or an illicit 

 process of one of the two extremes. It is not, indeed, very easy 

 fully to convict an argument of falling under any one of these 

 vicious cases in particular ; for the reason already more than 

 once referred to, that the premises are seldom formally set 

 out : if they were, the fallacy would impose upon nobody ; 

 and while they are not, it is almost always to a certain degree 

 optional in what manner the suppressed link shall be filled 

 up. The rules of the syllogism are rules for compelling a 

 person to be aware of the whole of what he must undertake 

 to defend if he persists in maintaining his conclusion. He 

 has it almost always in his power to make his syllogism good 

 by introducing a false premise ; and hence it is 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 com- 

 pelled distinctly to make his election what premises he is pre- 

 pared to maintain. The election made, there is generally so 

 little difficulty in seeing whether the conclusion follows from 

 the premises 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 certainly 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 premises. A proposition is proved, or an acknow- 

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

 and in the second a further argument is founded not on the 

 same proposition, but on some other, resembling it sufficiently 



