COMMON BASIS OF EMPIRICISM AND RATIONALISM 25 



a noise, and feel heat; this cannot be false; and this is what is 

 properly called perceiving (sentire), which is nothing else than 

 thinking." 1 



All this may be otherwise expressed by saying that rationalism, 

 as well as empiricism, acknowledges the absolute trustworthiness 

 of introspection as a source of truth. The difference between the 

 two schools on this score is due, first, to the improvement of the 

 method of introspection by Berkeley; and, secondly, to a conse- 

 quent great divergence of opinion as regards the actual contents 

 of the mind, revealed by introspection. The ultimate appeal, 

 however, is to the same supreme authority. 



The improvement in method is nowhere more strikingly illus- 

 trated than in the criticism of Descartes with which Berkeley 

 introduces his own theory of the visual perception of distance. 

 Descartes had seen that the altering convergence of the two eyes 

 plays a frequent part in such perception; and he promptly at- 

 tributed this part to the angle formed by the lines joining the 

 two eyes to the observed object. The greater the angle, the 

 nearer the object; and thus the idea of the angle must be the 

 basis for a judgment as to the distance. But this, Berkeley says, 

 is pure fiction. No such process of judgment takes place; and 

 the idea of the angle, upon which the judgment is supposed to 

 be based , is almost never present to consciousness. The defective- 

 ness of Descartes's procedure is that he allowed himself to specu- 

 late as to what must be in the mind in order to account for the 

 possibility of the given phenomenon (of distance-vision), instead 

 of basing his explanation upon such facts as were known from 

 direct observation. Since Berkeley's statement of the case is 

 very brief, and since it marks an epoch in the history of science, 

 a few lines may be profitably quoted. "It is evident that no idea 

 which is not itself perceived can be to me the means of perceiving 

 any other idea .... But those lines and angles by means where- 

 of some men pretend to explain the perception of distance are 

 themselves not at all perceived, nor are they in truth ever thought 



^Meditations, II; italics ours. 



