while those based upon assumption and deduction are comparatively 

 unbelievable. 



A close examination may reveal whether this relationship is an 

 accidental one, in this case, or whether it is a significant one which we 

 may expect to hold quite generally. The concepts which constitute 

 the essential materials for Darwin's theory are those of individual va- 

 riation, inheritance and natural selection. The existence of individual 

 variations, and their nature were experimentally investigated by Dar- 

 win : and may be by any other person. No one will doubt that there 

 are individual variations. So, also, the existence of natural selection, 

 and its nature, were directly investigated by Darwin, and may be by 

 any person wishing information concerning them. Or if any one 

 doubted either that individual variations and inheritance existed or 

 that natural selection operated, he could determine the facts by an 

 investigation of these forces. The conditions with regard to Locke's 

 theory, for example, are quite in contrast. Locke did not examine 

 the mind to determine its properties; he assumed it to have a certain 

 nature. And upon this assumption the validity of his theory rests, 

 as we have shown. The theory as presented by Locke offers no evi- 

 dence for the validity of the assumption, and no evidence exists for 

 it. The theory is in this peculiar position that it may sometime be 

 shown to be false, but never can be shown to be true; for if the only 

 dbjects with which the mind can be concerned were ideas, the mind 

 itself and the real things of Locke's theory could never be investigated, 

 nor the relationships between them. So the concepts which consti- 

 tute Locke's theory have never been subjected to experimental investi- 

 gation, but are purely hypothetical; and the theory is believable only 

 when one will accept the unsupported assumptions. 



The same contrast maintains between the theory of inorganic evo- 

 lution, based upon the method of experimentation, and the theory of 

 future life based upon the method of assumption and deduction. In 

 the theory of inorganic evolution, changes of temperature are tested 

 by instruments which experience has proved to be reliable. The pres- 

 ence or absence of a certain element can be certainly ascertained by 

 investigating the light emissions: this experience has verified. When 

 then the investigator, after a thorough examination, reports the differ- 

 ent temperatures of the Sun at different times, and the temperature of 

 the different stars, his results will not be doubted. Also his report that 

 some elements disappear and others appear is the direct outcome of an 

 experimental investigation. The concepts with which the theory deals 

 are experimental entities which any experimenter may, if he doubts, 

 determine the existence of. If any of the things which the theory 

 affirms to exist, did not exist; or if the nature of any thing was not 



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