:n. m.] TEE TEST OF TRUTH. 6.1 



ascribe the flow of a river to the same force which causes the 

 fall of a stone," and if, " in further explanation of a move- 

 ment produced by gravitation in a direction almost horizontal, 

 we cite the law that fluids subject to mechanical forces exert 

 reactive forces which are equal in all directions," we are going 

 through a process of demonstration, — we are including a 

 special fact under a more general fact. If now we seek the 

 warrant for this more general fact, and find it in that most 

 general fact that force persists, we are still going through a 

 process of demonstration. But if lastly we inquire for the 

 warrant of this most general fact, we shall get no reply save 

 that no alternative can be framed in thought. That force 

 persists we are compelled to believe, since the proposition that 

 force can arise out of nothing or can lapse into nothing is a 

 verbal proposition which we can by no amount of effort 

 translate into thought. Thus at the end of every demonstra- 

 tion we must reach an axiom for the truth of which our 

 only test is the inconceivability of its negation. 



Secondly, from a different point of view, a demonstration 

 is a series of propositions, every one of which is necessarily 

 involved in the preceding one. How do we know it to be 

 thus necessarily involved ? How do we know that the state- 

 ment that action and reaction are equal and opposite is 

 necessarily involved in the statement that force persists ? 

 Simply because we can conceive no alternative, since to do 

 so would be to perform the impossible task of formulating in 

 consciousness an equation between something and nothing. 

 Thus our only warrant for each step of a demonstration is 

 the fact that any alternative step is one which the mind 

 cannot take. 



Such is indeed our only warrant for that most certain of 

 all facts — the existence of our own states of consciousness. 

 If you say that you have a sensation of redness, and I 

 require you to prove the statement, you can only reiterate 

 that such is the fact, the testimony of consciousness as to the 



