FALLACIES OF CONFUSION. 399 



prove it, without knowing how, that he tries to establish his 

 premise by supposing proved what he is attempting to prove 

 by it. The most effectual way, in fact, of exposing a 

 Petitio Principii, when circumstances allow of it, is by 

 challenging the reason er to prove his premises ; which if 

 he attempts to do, he is necessarily driven into arguing in 

 a circle. 



It is not uncommon, however, for thinkers, and those 

 not of the lowest description, to be led, even in their own 

 thoughts, not indeed into formally proving each of two pro 

 positions from the other, but into admitting propositions 

 which can only be so proved. In the preceding example 

 the two together form a complete and consistent, though 

 hypothetical, explanation of the facts concerned. And the 

 tendency to mistake mutual coherency for truth ; to trust 

 one s safety to a strong chain though it has no point of sup 

 port ; is at the bottom of much which, when reduced to the 

 strict forms of argumentation, can exhibit itself no otherwise 

 than as reasoning in a circle. All experience bears testimony 

 to the enthralling effect of neat concatenation in a system 

 of doctrines, and the difficulty with which people admit the 

 persuasion that anything which holds so well together can 

 possibly fall. 



Since every case where a conclusion which can only be 

 proved from certain premises is used for the proof of those 

 premises, is a case of petitio principii, that fallacy includes a 

 very great proportion of all incorrect reasoning. It is neces 

 sary, for completing our view of the fallacy, to exemplify 

 some of the disguises under which it is accustomed to mask 

 itself, and to escape exposure. 



A proposition would not be admitted by any person in his 

 senses as a corollary from itself, unless it were expressed in 

 language which made it seem different. One of the com 

 monest modes of so expressing it, is to present the propo 

 sition itself in abstract terms, as a proof of the same propo 

 sition expressed in concrete language. This is a very 

 frequent mode, not only of pretended proof, but of pre 

 tended explanation ; and is parodied when Moliere makes 



