380 ELEMENTS OF SCIENCE 



breadth, and thickness. But ignorance how a thing has 

 come to be, does not in the least deprive us of our cer- 

 tainty of the fact that things are that we do know and 

 feel and live, and that dur body has the above- 

 mentioned dimensions i.e., that it is " extended." That 

 we have a power of feeling is evident to us by our 

 senses. That we exist, and know universal and neces- 

 sary truths, is plain because our existence and such 

 truths, have their evidence in themselves and need no 

 proof the ground on which we believe them is that 

 they are self-evident to us. 



But the student may ask whether there cannot be a 

 better criterion of truth than " self-evidence." Let us 

 then see whether or not it is possible to have a better. 

 Now, whatever the supreme and ultimate test of any 

 alleged truth may be, it must either reside in that truth 

 itself so making it luminously self-evident or in 

 something else, something external to it. But the 

 value of any external criterion could only be appreciated 

 by us through our perception of its cogency. If we 

 suddenly saw the law of contradiction written on a 

 cloud, or on the surface of the sun, such a fact 

 would not add to its cogency. In the first place, various 

 investigations might thereby be set on foot, such as the 

 sanity of a witness, or the probability of a common 

 simultaneous hallucination, and so on. But no one of 

 such investigations could come to any conclusion except 

 the principle of contradiction were first absolutely 

 accepted. Thus if a universal or necessary truth was 

 vouched for by some external criterion, the cogency of 

 which existed in that criterion itself, we should then 

 only have self-evidence after all, and " self-evidence" at 

 second hand, as regards the ultimate truth for which 

 such external criterion was to vouch. If, on the 



