70 The Scientific Method. 



and, to the question whether self-observation is the whole 

 fact of knowledge or only half that fact, it has no answer 

 except one which contradicts and destroys itself. 



This amazing internal self-contradiction in the answer 

 which idealism gives to the fundamental question of all 

 philosophy namely, " What can I know ? " is, of itself, the 

 unanswerable refutation of its claim to be philosophy at all. 

 Yet let us look further, since idealism and its offspring are 

 the only dangerous opponents of the scientific method out- 

 side of the circle of theological dogmatism. 



The scientific method is essentially summed up in the 

 three words observation, hypothesis, verification. The data 

 of observation, including both self-observation and world- 

 observation, comprise the whole materials of knowledge. 

 These materials idealism arbitrarily cuts down by half, and 

 its declaration that the individual can not observe a real ex- 

 ternal world is the distinctive idealistic principle. Since, 

 however, this principle, if logically carried out, asserts the 

 absolutely solitary existence of the individual thinker, and 

 therefore denies the existence of all other individuals, ideal- 

 ism, in order to rescue itself from patent and ridiculous ab- 

 surdity, supplements its idealistic principle by the realistic 

 inference that is, it allows itself to concede the existence 

 of a real external world so far as other individuals are con- 

 cerned, as a mere inference, postulate, or hypothesis, which 

 can never be converted into knowledge by any possible ob- 

 servation. We have seen that the idealistic principle destroys 

 itself by self-contradiction unless it is rigorously carried out 

 into positive denial of the existence of all individuals except 

 the solitary thinker ; or, in other words, that solipsism is the 

 only self -consistent form of idealism. But now let us ask, 

 What is the value of its alleged realistic inference ? 



I answer that this practical concession of the existence of 

 other individuals is no inference at all, has no logical value 

 whatever, and is at bottom nothing but a mere common- 

 sense belief, precisely similar to that " naive realism " which 

 idealists themselves are never tired of satirizing. The act- 

 ual existence of other individuals is not a question of infer- 

 ence at all, but a question of fact ; and no fact can be logic- 

 ally inferred from another fact. Inference remains mere 

 hypothesis until it has been converted into knowledge by 

 verification ; and all verification is fresh observation. That 

 is, mere unverified inference does not and can not infer a 

 fact, except as a merely possible fact ; it takes the verifica- 



