June 26, 1890] 



NATURE 



»95 



their present often scattered range. The great divisions 

 of the world into Palasogaea and Neogaea are confirmed 

 by palaeontology. Still more marked, however, is and 

 has been the contrast between Arcto- and Notogaea : so 

 that one feels inclined to suppose that the Neogaea is 

 only an exaggerated extension of the Notogaea. 



Such is a short outline of the contents of this book, 

 which, we feel sure, everyone interested in the study of 

 geographical zoology or of zoological geography, as the 

 case may be, will be pleased to read. 



H. Gadow. 



JEVONS AND MILL. 

 Pure Logic and other Minor Works. By W. S. Jevons. 

 Edited by Prof. Adamson and Harriet Jevons. 

 (London : Macmillan and Co., 1890.) 



THE services of the late Prof. W. S. Jevons to logic 

 were so eminent that considerable interest attaches 

 to his minor writings on that subject, which are now col- 

 lected into a volume. The earlier works, " Pure Logic " 

 and " The Substitution of Similars," which are contained 

 in the first and larger part of the volume, possess, indeed, 

 no more than a historic value. They expound his well- 

 known theory of equational logic, but for all practical 

 purposes they are replaced by the later and more inter- 

 esting exposition which is contained in the " Principles 

 of Science." 



The second part of the volume is a reprint of the 

 articles which Jevons contributed to the Contemporary in 

 criticism of J. S. Mill. A short chapter on the method 

 of difference is all that the editors were able to add to 

 them out of the mass of manuscript which the author had 

 in preparation for a systematic criticism. These essays 

 do not add to Jevons's reputation. They are a passionate 

 indictment of Mill's consistency : Jevons thought that 

 " Mill's mind was essentially illogical," and in the name 

 of logic he thought it his duty to undermine the authority 

 of Mill's writings. It may be doubted whether any work 

 of theory could bear such a strain of rigorous verbal pre- 

 cision as Jevons endeavours to impose upon Mill. How- 

 ever, not even the most devoted admirers of Mill would 

 maintain that Mill was a consistent thinker ; they would 

 find his merit elsewhere. To them and to others it will 

 seem that Jevons has left behind him a criticism far 

 worthier both of himself and of Mill, in the positive 

 advances which he made upon Mill's doctrines in his 

 own work on the principles of science, in the light which 

 he threw upon the fundamental nature of induction, upon 

 the function of hypothesis, and upon Mill's so-called 

 deductive method. 



Among the generation which is now entering upon 

 maturity many persons must have passed through a 

 similar history in their feelings with regard to Mill. 

 They became acquainted with his philosophy in youth, 

 and were carried away by its apparent clearness, its 

 freshness and youthful feeling, its love of truth, its 

 dignity, and the large views it gave them of human 

 thought and human life. It opened to them a new world 

 of thought and feeling. Afterwards, as they reflected 

 upon it, with the help of teachers anxious that en- 

 thusiasm should not blunt the edge of their pupils' 

 NO. 1078, VOL. 42] 



powers of rigorous thinking, they discovered that it 

 was riddled with contradictions real as well as verbal ; 

 was full of doctrines laid alongside of each other without 

 adjustment. By and by, when they recovered from the 

 shock of this discovery, they began to perceive that its 

 very errors were light-giving, that its inconsistencies were 

 due to Mill's large-mindedness, his susceptibility to every 

 side of a subject ; that where his reasoning was least 

 rigorous it was often most stimulating, and directed in- 

 quiry upon new and truer doctrines ; and perhaps they 

 often fell into the paradox of cherishing its errors above 

 its truths. Such persons will be inclined to resent a 

 criticism which contents itself with exposing the obvious 

 contradictions of Mill's philosophy. 



It is paying poor respect to a thinker to excuse his 

 want of consistency. But with a writer like Mill, above 

 all others, a mere destructive criticism conveys a positively 

 false impression. It is for any higher purpose of little 

 value, because it fails to point out the real significance of 

 the incriminated doctrines. And this is just the vice of 

 Jevons's attack. 



Let it be granted at once that Mill's doctrines of geo- 

 metrical axioms, of the foundation of induction, of 

 pleasure, contain glaring contradictions. Mill holds that 

 geometrical axioms are derived from experience ; but 

 while he admits that there is no such thing in existence 

 as a straight line, he declares that we can reason about 

 straight lines because our ideas of spatial figures exactly 

 correspond to the reality. He declared that all induction 

 rests ultimately, in a syllogistic relation, upon the law of 

 causation, and at the same time that this principle is 

 itself derived from particular inductions by the process 

 of simple enumeration, which he elsewhere stigmatizes as 

 vicious. With a theory of pleasure not different in 

 principle from that of Hume and Bentham, he at the 

 same time asserts a distinction of pleasures in kind. In 

 exposing these contradictions, as well as in pointing out 

 the difficulties of the method of difference, Jevons is 

 completely successful ; but in leaving the reader to infer 

 that Mill's doctrines are therefore valueless he omits the 

 most necessary part of the critic's task. Mill distinctly 

 says that the axiom that two straight lines cannot inclose 

 a space represents the limit to which many actual ex- 

 periences approximate. It is true that he did not solve 

 the ultimate difficulty of the relation to reality of such a 

 limiting proposition — call it a hypothesis, or call it an 

 ideal experiment. But, in spite of the gratuitous incon- 

 sistencies he introduces into the argument. Mill's conten- 

 tion remains unassailed that geometrical truths derive 

 their authority from the same source as all other truths. 

 With regard to the basis of induction, a more impartial 

 criticism would have pointed out that Mill failed because 

 he was untrue to himself. His doctrine of the syllogism 

 is one of the most important contributions ever made to 

 logic, but if he had been true to it he would have given 

 to the law of universal causation as major premiss of the 

 inductive syllogism a function like that which he assigns 

 to the major premiss of every syllogism, and both secured 

 the consistency of his whole theory as well as the truth 

 of this particular doctrine. His distinction of pleasures 

 according to kind is impossible on his own theory, its 

 real position in his mind uncertain, and its suggestiveness 

 in any case small ; but, with its appeal to the judgment of 



