Sentence:  `` History has this in common with every other science : that the historian is not allowed to claim any single piece of knowledge , except where he can justify his claim by exhibiting to himself in the first place , and secondly to any one else who is both able and willing to follow his <WSD>demonstration</WSD> , the grounds upon which it is based . 
Meaning of the word marked with <WSD> tags:  proof by a process of argument or a series of proposition proving an asserted conclusion