498 NATURAL SCIENCE. sept.. 



to also recognise what they do know, what they must know if they 

 know anything, and what is that soHd foundation on which alone 

 they can securely rear any self-consistent and stable fabric of 

 knowledge. 



It would occupy too much space were I to enter upon any 

 defence of the evident and fundamental truths of science, nor is it 

 needful, as I have done so elsewhere both briefly^ and also more at 

 length.'' 



There are four essential truths concerning what we know : — 



1. We can know not only our actions, sensations, imaginations, 

 reminiscences, emotions, perceptions, and conceptions, but also our 

 own substantial and continuous personal existence.s 



2. We know, through memory, real existences external to all our 

 present experience, i.e., we have the faculty of knowing what, pace 

 Mr. Ryle, is objective truth.^ 



3. We know that there are truths which are true not only here and 

 now, but which must be true ever and always — as that " nothing can 

 at the same time both be and not be. "7 We know this to be not merely 

 a law or condition of our own mind, but that it is true of all " things- 

 in-themselves " apart from the existence of any or every mind. 



4. We know that, if certain principles be true, then whatever 

 logically follows from them must be true likewise.^ 



Unless we know these things science is logically impossible, and 

 any scientific man who denies them either deceives himself or seeks 

 to deceive others. Without them it is impossible to have — what 

 alone should satisfy a man of science — a system of knowledge com- 

 plete and harmonious, satisfactory and stable, from its deepest 

 foundation to its loftiest pinnacle. 



If these truths are really doubted or denied by anyone, he must 

 fall into a state of mental paralysis and intellectual inanition ; 

 though, of course, men may really hold and act on them, while sup- 

 posing or pretending they do nothing of the kind,9 there being so 

 much both of stupidity and dishonesty in the world. 



Really, however, to believe that any appeal lies to sensation from 

 that which the intellect declares to be evidently true, is a self- 

 stultifying belief. How, save by the intellect, can we know that we 

 possess a sensitive faculty, or that we have '* sense-impressions " and 

 ** sense-impresses " at all ? 



But if we know so much, i.e., if we know the four truths above 

 enumerated — what difficulty is there in recognising that we may 

 know and do know yet more ? 



* See Nature, Nov. 19, 1891, pp. 60-62; and Nov. 26, pp. 82-85; also Supple- 

 mentary Notes in the numbers for Jan. 7, 1892, p. 222, and Feb. 11, p. 343. 

 ■• See On Truth, a Systematic Inquiry, Kegan Paul, Trench & Co., 1889. 

 "^ See On Truth, pp. 3-28. "^ Op. n't., pp. 29-37. 



7 Op. cit., pp. 39-46. » op. at , pp. 53 59 



9 Op. cit., pp. 134. 135. 



