572 FALLACIES. 



premise by supposing proved Avhat he is attempting to prove by it. The 

 most effectual way, in fact, of exposing a petitio principii, when circum- 

 stances allow of it, is by challenging the reasoner 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 propositions from the other, but into admitting propo- 

 sitions 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 

 support^s 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 concatena- 

 tion in a system of doctrines, and the difficulty with which people admit the 

 persuasion that any thing which holds so well together can possibly fall. 



Since every case where a conclusion which can only be proved from cer- 

 tain 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 rea- 

 soning. It is necessary, for completing our view of the fallacy, to exempli- 

 fy 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 commonest modes of so expressing it, is to 

 present the proposition itself in abstract terms, as a proof of the same 

 proposition expressed in concrete language. This is a very frequent mode, 

 not only of pretended proof, but of pretended explanation ; and is parodied 

 when Moliere {Le Malade Imaginaire) makes one of his absurd physi- 

 cians say, 



Mihi a docto doctore, 



Demandatiu- causam et rationem quare 

 Opium facit dormire. 



A quoi lespondeo, 



Quia est in eo 



Virtus dorniitiva, ' 



Cujus est natura 



Sensus assoupire. 



The words Nature and Essence are grand instruments of this mode of 

 begging the question, as in the well-known argument of the scholastic 

 theologians, that the mind thinks always, because the essence of the mind 

 is to think. Locke had to point out, that if by essence is here meant some 

 property which must manifest itself by actual exercise at all times, the 

 premise is a direct assumption of the conclusion ; while if it only means 

 that to think is the distinctive property of a mind, there is no connection 

 between the premise and the conclusion, since it is not necessary that a dis- 

 tinctive property should be perpetually in action. 



The following is one of the modes in which these abstract terms, Nature 

 and Essence, are used as instruments of this fallacy. Some particular prop- 

 erties of a thing are selected, more or less arbitrarily, to be termed its nature 

 or essence; and when this has been done, these properties are supposed to 

 be invested with a kind of indefeasibleness; to have become paramount to 

 all the other properties of the thing, and incapable of being prevailed over 



