LOGIC. 



while most related to matters quite different. As 

 many of the designations have come into familiar 

 use, it is proper to take notice of the leading 

 cases. 



The undistributed middle is a pure breach of 

 syllogism. ' A term is said to be " distributed " 

 when it is taken universally so as to stand for 

 everything it is capable of being applied to ; and 

 consequently " undistributed," when it stands for 

 a portion only of the things signified by it. Thus, 

 " all food," or every kind of food, are expressions 

 which imply the distribution of the term " food ; " 

 " some food " would imply its non-distribution.' 

 The syllogism, ' Food is necessary to life ; corn is 

 food ; therefore corn is necessary to life,' is faulty 

 from undistributed middle ; inasmuch as the 

 affirmation, 'food is necessary,' c. has the form 

 of a universal proposition, with the reality of a 

 particular one. 



The ceqztivocatio is when a word is used in two 

 different senses, giving really no middle term if 

 the middle term be in question or a term in the 

 conclusion which is not the same name as that 

 used in the premises. For example, ' All criminal 

 actions ought to be punished by law ; prosecutions 

 for theft are criminal actions ; therefore prosecu- 

 tions for theft ought to be punished by law.' 

 Here the middle term is doubly ambiguous, both 

 criminal and action having different senses in the 

 two premises. 'The following example can be 

 traced through books for three centuries : " Every 

 dog runs on four legs ; Sirius (the dog-star) is a 

 dog ; therefore Sirius runs on four legs." ' 



' The fallacia compositionis and fallacia divi- 

 sionis consist in joining or separating those things 

 which ought not to be joined or separated. Thus, 

 " two and three are even and odd ; but five is not 

 even and odd."' 



' The fallacia accentus was an ambiguity arising 

 from pronunciation. A very forced emphasis 

 upon one word may, according to usual notions, 

 suggest false meanings. Thus, " thou shalt not 

 bear false witness against thy neighbour," is fre- 

 quently read from the pulpit either so as to convey 

 the opposite of a prohibition, or to suggest that 

 subornation is not forbidden, or that anything 

 false except evidence is permitted, or that it 

 may be given for him, or that it is only against 

 neighbours that false witness may not be borne.' 



' All these fallacies in dictione come under the 

 head of ambiguous language, and amount to 

 nothing but giving the syllogism four terms, two 

 of them under the same name. The fallacies 

 extra dictionem (apart from or unconnected with 

 the language) are set down as follows : 



' The fallacia accidentis (judging of a thing by 

 some accidental property), and that a dicto secun- 

 dum quid ad dictum simpliciter (passing from 

 what is true in some respect to what is true abso- 

 lutely). The first consists in inferring of the sub- 

 ject with an accident that which was premised of 

 the subject only ; the second, in inferring of the 

 subject only that which was premised of the sub- 

 ject with an accident. Of the first, we may give 

 the instance : " Wine is pernicious ; therefore it 

 ought to be forbidden." The expressed premise 

 refers to wine used immoderately ; the conclusion 

 is meant to refer to wine however used.' * 



1\& petitio principiiy or begging of the question, 



De Morgan's Formal Logic, chap. xiii. 



is one of the logical terms that has found its way 

 into ordinary life. ' Galileo has charged Aristotle 

 himself with having fallen into this error, when he 

 tried to prove that the earth was at the centre of 

 the world by this argument : 



' The nature of heavy things is to tend to the 

 centre of the universe, and of light things to go off 

 from it ; 



' Now, experience proves that heavy things tend 

 towards the centre of the earth, and that light 

 things go off from it ; 



' Therefore the centre of the earth is the same 

 as the centre of the universe. 



' It is clear that there is in the major of this 

 argument a manifest begging of the question; 

 for we see well enough that heavy things tend 

 towards the centre of the earth ; but where did 

 Aristotle learn that they tend towards the centre 

 of the universe, unless he assumed that the centre 

 of the earth is the same as the centre of the 

 universe ? which is the very conclusion he wishes 

 to prove by that argument.' * 



Arguing in a circle is at bottom the very same 

 fallacy. 



' The ignoratio elenchi, or ignorance of the 

 refutation, is what we should now call answering 

 to the wrong point ; or proving something which is 

 not contradictory of the thing asserted. It may 

 be considered either as an error of form or of 

 matter ; and it is, of all the fallacies, that which 

 has the widest range.' 



The argumenta ad hominem, 'having some 

 reference to the particular person to whom the 

 argument is addressed, will generally be found to 

 partake of the above fallacy. Such are recrim- 

 ination and charge of inconsistency, as : " You 

 cannot use this assertion, because in such another 

 case you oppose it." But if the original argument 

 itself should be a personal attack, then such a 

 retort as the preceding may be a valid defence.' 



'The fallacia consequentis (now very often 

 called a non sequitur} is the simple affirmation 

 of a conclusion which does not follow from the 

 premises.' 



The non causa pro causa. This is a fallacy of 

 insufficient induction, or the inferring of a connec- 

 tion of cause and effect where there is only a 

 mere sequence as in the celebrated instance of 

 the rustic who made Tenterden steeple the cause 

 of Goodwin Sands. The words post hoc, ergo 

 propter hoc, also express the same fallacious tend- 

 ency to ascribe a necessary connection between 

 two things that happen to occur in succession. 

 This is the great argument in favour of every 

 medicine that has been believed efficacious : some 

 one had it, and got better. 



'The fallacia plurium interrogationum consists 

 in trying to get one answer to several questions in 

 one. It is sometimes used by barristers in the 

 examination of witnesses, who endeavour to get 

 yes or no to a complex question which ought to be 

 partly answered in each way, meaning to use the 

 answer obtained, as for the whole, when they have 

 got it for a part/t 



THE LOGIC OF THE SCIENCES. 



The general laws and abstractions that are 

 arrived at by the methods above described, are 



Port Royal Logic, part III. chap, xix. 

 f De Morgan, p. 269. 



363 



