PROLEGOMENA. XVii. 



have his own particular truth ; as visionaries and 

 madmen, who believe in their illusive sensations ; 

 if we admit to its fullest extent the right of private 

 judgment. There must, therefore, be some 

 general standard of truth. Let us examine what 

 this standard is. We shall find that it is no 

 other than authority, which in this case is almost 

 universal or of the highest kind, as it takes in the 

 whole of mankind not manifestly disordered, by 

 whose consent of judgment the illusions of the 

 maniac are detected. For example, suppose a 

 man were to get up in the middle of the streets 

 of London, and assert himself to be Emperor of 

 China ; he would be condemned by the general 

 consent of the citizens as a madman, however 

 forcibly his illusive conceit might to him be truth. 

 But it cannot be the assertion, that he is Emperor 

 of China alone that constitutes insanity ; while 

 there is another man at Pekin, who would equally 

 be deemed mad if he were to deny himself to 

 be such. The reason why one is reckoned mad 

 and the other sound for asserting the same (hinsr 

 is, because in the one case the authority of 

 mankind consents to, and in the other dissents 

 from, the assertion and troth of the individual. 



But I will solve the question in a more 

 simple manner. We know tliat there is a disease 

 not uncommon, which produces those illusive 

 sensations, called Spectra, or images presented 



B 



