44 



DR. LUDWIG VOX GERDTELI.^ OX 



hypothesis, which, in its origin, differs not at all from any other 

 hypothesis : it is a rational idea which is forced upon the 

 student of nature as he advances into his analysis of actualities, 

 the soundness of which he continually proves by experience. 

 Let us take a concrete example : why do we decide 



(1) That every stone thrown upwards into the air will fall 



back to the earth, if nothing but air pressure resists 

 it : and 



(2) That, if the object does not return, there must have 



been some preventative element, such as, for instance, 

 a shock to shatter into dust, or a whirhvind, or the like. 



The answer is this : from abundant experience, in which the 

 apparent exceptions are attributable as a rule to imperfect 

 observation, and which has been verified by numerous tests, the 

 main conclusion has been reached : we believe tliat it will 

 always be so, because it has always been so. We have no 

 reason to doubt it, and therefore we call our conclusion " Know- 

 ledge." For practical life this " knowledge " has shown itself 

 to be so valuable and satisfactory that it would be foolish to 

 depend upon any other premiss (Georg Eunze, Metaphysik, 

 1905). AVhen we fire a shot into the air and fail to find it 

 again, we know as a practical certainty that the shot has not 

 disappeared into the cosmos and lighted perliaps on Sirius, but 

 that it has fallen somewhere on the earth. But this practical 

 certainty is, as a matter of exact theory, not proved or 

 apodictical knowledge," but only a w^ell-grounded conviction 

 of a high degree of credibility : theoretically considered, it 

 would at least be conceivable that a bullet might, under 

 different conditions, escape into the cosmos. But, so far as 

 experience goes, bodies ahvays return to earth. We therefore 

 assume that in agreement with previous experience, all bullets 

 discharged from a rifie return as a matter of course and 

 practical certainty to earth, even when we have no evidence of 

 their whereabouts. And we have a right to this assumption 

 until a case occurs which can be proved to be an exception. 



But this practical certainty must not for a moment be 

 allowed to lead us into the eiTor of thinking that the Causal 

 principle is aught else than hypothesis. To be sure, the Causal 

 principle is a hypothesis of a remarkable kind. It differs from 

 all other hypotheses which enter into Natural Law in these 

 respects : 



(1) It is a hypothesis with which we approach every future 

 possible occurrence in Nature. We expect every 



