JOHN STUART MILL'S PHILOSOPHY TESTED. 



285 



lines exist, and, correcting this blunder of fact, 

 the logical contradiction vanishes. Certainly he 

 gives no proper reason for his confident denial of 

 their existence. But merely to strike out a page 

 of Mill's Logic will not vindicate his logical char- 

 acter. How came he to put a statement there 

 which is in absolute conflict with the rest of his 

 arguments ? No interval of time, no want of 

 revision, can excuse this inconsistency, for the 

 passage occurs in the first edition of the " System 

 of Logic" (vol. i., p. 297), and reappears un- 

 changed (except as regards one word) in the last 

 and ninth edition. The curious substitution of 

 the words " not strictly true " for the word " false " 

 shows that Mill's attention had been directed to 

 the paragraph ; and a good many remarks might 

 be made upon this little change of words, were 

 there not other matters claiming prior attention. 

 We have seen that Mill considers our knowl- 

 edge of geometry to be founded to a great extent 

 on mental experimentation. I am not aware that 

 any philosopher ever previously asserted, with 

 the same distinctness and consciousness of his 

 meaning, that the observation of our own ideas 

 might be substituted for the observation of things. 

 Philosophers have frequently spoken of their 

 ideas or notions, but it was usually a mere form 

 of speech, and their ideas meant their direct 

 knowledge of things. Certainly this was the case 

 with Locke, who was always talking about ideas. 

 Descartes, no doubt, held that whatever we can 

 clearly perceive is true ; but he probably meant 

 that it would be logically possible. I do not 

 think that Descartes in his geometry ever got to 

 mental experimentation. But, however, this may 

 be, Mill, of all men, ought not to have recom- 

 mended such a questionable scientific process, 

 if we may judge from his statements in other 

 parts of the "System of Logic." The fact is 

 that Mill, before coming to the subject of Geome- 

 try, had denounced the handling of ideas instead 

 of things as one of the most fatal errors — indeed, 

 as the cardinal error of logical philosophy. In 

 the chapter upon the "Nature and Import of 

 Propositions," ' he says: 



" The notion that what is of primary impor- 

 tance to the logician in a proposition, is the rela- 

 tion between the two ideas corresponding to the 

 subject and predicate (instead of the relation be- 

 tween the two phenomena which they respectively 

 express), seems to me one of the most fatal errors 

 ever introduced into the philosophy of Logic ; and 

 the principal cause why the theory of the science 

 has made such inconsiderable progress during the 



1 Book I., chapter v., section 1, fifth paragraph. 



last two centuries. The treatises on Logic, and 

 on the branches of Mental Philosophy connected 

 with Logic, which have been produced since the 

 intrusion of this cardinal error, though sometimes 

 written by men of extraordinary abilities and at- 

 tainments, almost always tacitly imply a theory 

 that the investigation of truth consists in contem- 

 plating and handling our ideas, or conceptions of 

 things, instead of the things themselves : a doc- 

 trine tantamount to the assertion that the only 

 mode of acquiring knowledge of Nature is to 

 study it at second hand, as represented in our 

 own minds." 



Mill here denounces the cardinal error of in- 

 vestigating Nature at second hand, as represent- 

 ed in our own minds. Yet bis words exactly de- 

 scribe that process of mental experimentation 

 which he has unquestionably advocated in geom- 

 etry, the most perfect and certain of the sci- 

 ences. 



It may be urged, indeed, with some show of 

 reason, that the method which might be erro- 

 neous in one science might be correct in another. 

 The mathematical sciences are called the exact 

 sciences, and they may be of peculiar character. 

 But, in the first place, Mill's denunciation of the 

 handling of ideas is not limited |>y any excep- 

 tions ; it is applied in the most general way, and 

 arises upon the general question of the Import 

 of Propositions. It is, therefore, in distinct con- 

 flict with Mill's subsequent advocacy of mental 

 experimentation. 



In the second place, Mill is entirely precluded 

 from claiming the mathematical sciences as pecul- 

 iar in their method, because one of the principal 

 points of his philosophy is to show that they are 

 not peculiar. It is the outcome of his philosophy 

 to show that they are founded on a directly em- 

 pirical basis, like the rest of the sciences. He 

 speaks l of geometry as a " strictly physical sci- 

 ence," and asserts that every theorem of geome- 

 try is a law of external Nature, and might have 

 been ascertained by generalizing from observa- 

 tion and experiment. 5 What will our physicists 

 say to a strictly physical science, which can be 

 experimented on in the private laboratory of the 

 philosopher's mind ? What a convenient sci- 

 ence ! What a saving of expense in regard of 

 apparatus, and materials, and specimens ! 3 



1 Book III., chapter xxiv., section 7, about the 

 tenth line. 



5 Same section, beginning of second paragraph. 



3 Since writing the above, I have made the signifi- 

 cant discovery that in the first and second editions a 

 clause follows the passage quoted from Book I., chap- 

 ter v., section 1, paragraph 5 (vol. i., middle of page 



