512 FALLACIES. 



doctrines, and the difficulty with which men 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 premisses is used for the proof of those premisses, is a case of 

 petitio jJrincipii, that fallacy includes a very great proportion of all in- 

 coiTect reasoning. It is necessary, 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 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 explana- 

 tion ; and is parodied by Moliere vdien he makes one of his absurd 

 physicians say, "I'opium endormit parcequ'il a une vertu soporifique," 

 or, in the amusing doggerel quoted by Mr. Whewell — 



Mihi demandatur 



A (loctissimo doctore, 

 Quare opium facit dormire ; 



Et ego respondeo, 



Quia est in eo 



Virtus dormitiva, 

 Cujus natura est sensus assopire. 



The words Nature and Essence are grand instruments of this mode 

 of begging the question. As in the well-known al"gument of the scho- 

 lastic 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 exer- 

 cise at all times, the premiss 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 connexion between the premiss and the conclusion, 

 since it is not necessary that a distinctive property should be pei-pet- 

 ually in action. 



The following is one of the modes in which these abstract tei-ms, 

 Nature and Essence, are used as instruments of this fallacy. Some 

 particular properties 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 indefeasible- 

 ness ; to have become paramount to all the other properties of the 

 thing, and incapable of being prevailed over or counteracted by them. 

 As when Aristotle, in a passage which we have already cited from Mr. 

 Whewell, " decides that there is no void on such arguments as this : 

 in avoid there could be no difference of up and down; for as in 

 nothing there are no differences, so there are none in a privation or 

 negation; but a void is merely a privation or negation of matter; 

 therefore, in a void, bodies could not move up and down, which it is 

 in their nature to do."* In other words ; It is the nature of bodies to 

 move up and down, ergo any physical fact which supposes them not 

 so to move, cannot be authentic. This mode of reasoning, by which 

 a bad generalization is made to overrule all facts which contradict it, 

 is petitio principii in one of its most palpable forms. 



* Wheweix's History of the Inductive Scietices, i, 44. 



