THE FACTS OF SCIENCE 53 



^ 7. — The Scientific Validity of a Conception 



In order that a conception may have scientific vaHdity, 

 it must be self- consistent, and deducible from the per- 

 ceptions of the normal human being. For instance, a 

 centaur is not a self-consistent conception ; as soon as our 

 knowledge of human and equine anatomy became 

 sufficiently developed, the centaur became an unthinkable 

 thing — a self-negating idea. As the man-horse is seen 

 to be a compound of sense-impressions, which are irrecon- 

 cilable anatomically, so the man-god, whose cruder type is 

 Hercules, is also seen to be a chimera, a self-contradictory 

 conception, as soon as we have clearly defined the physical 

 and mental characteristics of man. But even if an indi- 

 vidual mind has reached a conception, which at any rate 

 for that mind is perfectly self- consistent, it does not 

 follow that such a conception must have scientific validity, 

 except as far as science may be concerned with the 

 analysis of that individual mind. When a person 

 conceives that one colour — green — suffices to describe 

 the flowers and leaves of a rose-tree in my garden, I 

 know that his conception may, after all, be self-consistent, 

 it may be in perfect harmony with his sense-impressions. 

 I merely assert that his perceptive faculty is abnormal, 

 and hold him to be colour-blind. I may study the 

 individual abnormality scientifically, but his conception 

 has no scientific validity, for it is not deducible from the 

 perceptions of the normal human being. Here indeed 

 we have to proceed very cautiously if we are to determine 

 what self- consistent conceptions have scientific validity. 

 Above all, we must note that a conception does not cease 

 to be valid because it has not been deduced by the 

 majority of normal human beings from their perceptions. 

 The conception that a new individual will originate from 

 the union of a male and female cell may never have 

 actually been deduced by a majority of normal human 

 beings from their perceptions. But if any normal human 

 being be trained in the proper methods of observation, 

 and be placed in the right circumstances for investigating, 



