CHAPTER XVIII 

 NECESSARY TRUTH 



Idealism and experience Common-sense and experience Kinds of pro- 

 perties The limits within which we can know and think Truths reached through 

 simple enumerations Necessary truths Mathematical axioms Cause and effect 

 Causation is a common-sense notion Science is common sense Thorough- 

 going idealism is unassailable, but leads to a cul-de-sac. 



568. A LL knowledge, all thinking is founded ultimately on 

 /\ experience that has been stored by the memory. 

 "* -^" Experience begins with sense-impressions. The 

 one thing that no one can doubt is the existence of his own 

 feelings. There lies before me what common-sense regards as a 

 sheet of paper. I may, after much thought, have doubts about 

 the existence of that sheet, but I can have none about the existence 

 of the sensations that seem to reveal it to me nor of my thoughts 

 about them. If I think as a thorough-going idealist, I can note 

 these feelings ; if I go so far as to use the coherence of thought 

 that common sense has established, I can also observe and re- 

 member their co-existences and sequences. But there the matter 

 ends. The origin of them and of their co-existences and sequences 

 remains an unfathomable mystery. On the other hand, if I make 

 the assumption which common sense makes, if I suppose that the 

 sheet has a real existence external to me and that my feelings 

 are aroused by the properties or qualities of it, then the matter 

 does not end there. A limitless field of thought opens up. If this 

 object has a real existence and certain properties, then innumerable 

 other objects have real existences and properties which are not 

 merely my feelings but the exciting cause of them. Above all, 

 just as the properties of the sheet of paper and those of my mind 

 bring the two things into relation, so are all other things brought 

 into relation by means of their properties. In this way the 

 universe is linked together and becomes a unity. 



569. If, then, the assumption that there is a universe external 

 to my mind, and that it is revealed to me by my feelings, be given, 

 it follows that, though knowledge begins with sense-impressions, 



