264 RECENT PROGRESS OF THE THEORY OF VISION. 



answer for any other. Then, in order to help out the hypothesis, 

 the very doubtful assumption has to be made that, in these 

 other cases, sensation is overcome and extinguished by opposing 

 experience. But what confidence could we put in any of our 

 perceptions if we were able to extinguish our sensations as we 

 please, whenever they concern an object of our attention, for 

 the sake of previous conceptions to which they are opposed 1 

 At any rate, it is clear that in every case where experience must 

 finally decide, we shall succeed much better in forming a correct 

 notion of what we see, if we have no opposing sensations to 

 overcome, than if a correct judgment must be formed in spite 

 of them. 



It follows that the hypotheses which have been successively 

 framed by the various supporters of intuitive theories of vision, 

 in order to suit one phenomenon after another, are really quite 

 unnecessary. No fact has yet been discovered inconsistent with 

 the Empirical Theory : which does not assume any peculiar 

 modes of physiological action in the nervous system, nor any 

 hypothetical anatomical structures ; which supposes nothing 

 more than the well-known association between the impressions 

 we receive and the conclusions we draw from them, according 

 to the fundamental laws of daily experience. It is true that 

 we cannot at present offer any complete scientific explanation 

 of the mental operations involved, and there is no immediate 

 prospect of our doing so. But since these operations actually 

 exist, and since hitherto every form of the intuitive theory has 

 been obliged to fall back on their reality when all other explana- 

 tion failed, these mysteries of the laws of thought cannot be 

 regarded from a scientific point of view as constituting any 

 deficiency in the Empirical Theory of Vision. 



It is impossible to draw any line in the study of our percep- 

 tions of space which shall sharply separate those which belong 

 to direct Sensation from those which are the result of Expe- 

 rience. If we attempt to draw such a boundary, we find that 

 experience proves more minute, more direct and more exact 

 than supposed sensation, and in fact proves its own superiority 

 by overcoming the latter. The only supposition which does 



