574 FALLACIES. 



acters by the phrases referred to ; but that such could have been the mean- 

 ing intended is very unlikely, considering the contempt of the ancient phi- 

 losophers for vulgar opinion. In any other sense they are clear cases of 

 Petitio Principii, since the word laudable, and the idea of boasting, im- 

 ply principles of conduct; and practical maxims can only be proved from 

 speculative truths, namely, from the properties of the subject-matter, and 

 can not, therefore, be employed to prove those properties. As well might 

 it be argued that a government is good because we ought to support it, or 

 that there is a God because it is our duty to pray to him. 



It is assumed by all the disputants in the "De Finibus" as the founda- 

 tion of the inquiry into the summum bonum, that " sapiens semper beatus 

 est." Not simply that wisdom gives the best chance of happiness, or that 

 wisdom consists in knowing what happiness is, and by what things it is 

 promoted ; these propositions would not have been enough for them ; but 

 that the sage always is, and must of necessity be, happy. The idea that 

 wisdom could be consistent with unhappiness, was always rejected as inad- 

 missible: the reason assigned by one of the interlocutors, near the begin- 

 ning of the third book, being, that if the wise could be unhappy, there was 

 little use in pursuing wisdom. But by unhappiness they did not mean 

 pain or suffering ; to that it was granted that the wisest person was liable 

 in common with others : he was happy, because in possessing wisdom he 

 had the most valuable of all possessions, the most to be sought and prized 

 of all things, and to possess the most valuable thing was to be the most 

 happy. By laying it down, therefore, at the commencement of the inquiry, 

 that the sage must be happy, the disputed question respecting the sum- 

 mum honum, was in fact begged ; with the further assumption, that pain 

 and suffering, so far as they can co-exist with wisdom, are not unhappiness, 

 and are no evil. 



The following are additional instances of Petitio Principii, under more 

 or less of disguise. 



Plato, in the Sophistes, attempts to prove that things may exist which 

 are incorporeal, by the argument that justice and wisdom are incorporeal, 

 and justice and wisdom must be something. Here, if by something be 

 meant, as Plato did in fact mean, a thing capable of existing in and by 

 itself, and not as a quality of some other thing, he begs the question in 

 asserting that justice and wisdom must be something ; if he means any 

 thing else, his conclusion is not proved. This fallacy might also be class- 

 ed under ambiguous middleterm ; something, in the one premise, meaning 

 some substance, in the other merely some object of thought, whether sub- 

 stance or attribute. 



It was formerly an argument employed in proof of what is now no long, 

 er a popular doctrine, the infinite divisibility of matter, that every portion 

 of matter however small, must at least have an upper and an under sur 

 face. Those who used this argument did not see that it assumed the very 

 point in dispute, the impossibility of arriving at a minimum of thickness; 

 for if there be a minimum, its upper and under surface will of course be 

 one ; it will be itself a surface, and no more. The argument owes its very 

 considerable plausibility to this, that the premise does actually seem more 

 obvious than the conclusion, though really identical with it. As expressed 

 in the premise, the proposition appeals directly and in concrete language 

 to the incapacity of the human imagination for conceiving a minimum. 

 Viewed in this light, it becomes a case of the a priori fallacy or natural 

 prejudice, that whatever can not be conceived can not exist. Every fal- 



