560 FALLACIES. 



consequent be false, the antecedent is false ; but this, If the consequent be 

 true, the antecedent is true, by no means holds good, but is an error corre- 

 sponding to the simple conversion of a universal affirmative. Yet hardly 

 any thing is more common than for people, in their private thoughts, to 

 draw this inference. As when the conclusion is accepted, which it so oft- 

 en is, for proof of the premises. That the premises can not be true if 

 the conclusion is false, is the unexceptionable foundation of the legitimate 

 mode of reasoning called reductio ad absurdum. But people continually 

 think and express themselves, as if they also believed that the premises 

 can not be false if the conclusion is true. The truth, or supposed truth, of 

 the inferences which follow fi"om a doctrine, often enables it to find accept- 

 ance in spite of gross absurdities in it. How many philosophical systems 

 which had scarcely "any intrinsic recommendation, have been received by 

 thoughtful men because they were supposed to lend additional support to 

 religion, morality, some favorite view of politics, or some other cherished 

 persuasion: not merely because their wishes were thereby enlisted on its 

 side, but because its leading to what they deemed, sound conclusions ap- 

 peared to them a strong presumption in favor of its truth : though the 

 presumption, when viewed in its true light, amounted only to the absence 

 of that particular evidence of falsehood, which would have resulted from 

 its leading by correct inference to something already known to be false. 



Again, the very frequent error in conduct, of mistaking reverse of wrong 

 for right, is the practical form of a logical eri-or with respect to the Oppo- 

 sition of Propositions. It is committed for want of the habit of distin- 

 guishing the contrary of a proposition from the contradictory of it, and 

 of attending to the logical canon, that contrary propositions, though they 

 can not both be true, may both be false. If the error were to express it- 

 self in words, it would run distinctly counter to this canon. It generally, 

 however, does not so express itself, and 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 syl- 

 logism, either avowedly, or in the covert mode of an undistributed middle 

 term, 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 powerto 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 syllo- 

 gism: but this detracts nothing from the value of the syllogistic rules, 

 since it is by thera that a reasoner is compelled distinctly to make his elec- 

 tion what premises he is prepared 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 improprie- 

 ty have merged this fourth class of fallacies in the fifth, or Fallacies of 

 Confusion. 



