92.  In order to disentangle our minds from whatever prejudices we may entertain with relation to the subject in hand, nothing seems more apposite than the taking into our thoughts the case of one born blind, and afterwards, when grown up, made to see.  And though, perhaps, it may not be an easy task to divest ourselves entirely of the experience received from sight, so as to be able to put our thoughts exactly in the posture of such a one’s, we must, nevertheless, as far as possible, endeavour to frame true conceptions of what might reasonably be supposed to pass in his mind.

93.  It is certain that a man actually blind, and who had continued so from his birth, would by the sense of feeling attain to have ideas of upper and lower.  By the motion of his hand he might discern the situation of any tangible object placed within his FI reach.  That part on which he felt himself supported, or towards which he perceived his body to gravitate, he would term lower, and the contrary to this upper; and accordingly denominate whatsoever objects he touched.

94.  But then, whatever judgments he makes concerning the situation of objects are confined to those only that are perceivable by touch.  All those things that are intangible and of a spiritual nature, his thoughts and desires, his passions, and in general all the modifications of the soul, to these he would never apply the terms upper and lower, except only in a metaphorical sense.  He may, perhaps, by way of allusion, speak of high or low thoughts:  but those terms in their proper signification would never be applied to anything that was not conceived to exist without the mind.  For a man born blind, and remaining in the same state, could mean nothing else by the words higher and lower than a greater or lesser distance from the earth; which distance he would measure by the motion or application of his hand or some other part of his body.  It is therefore evident that all those things which, in respect of each other, would by him be thought higher or lower, must be such as were conceived to exist without his mind, in the ambient space.

95.  Whence it plainly follows that such a one, if we suppose him made to see, would not at first sight think anything he saw was high or low, erect or inverted; for it hath been already demonstrated in sect. 41 that he would not think the things he perceived by sight to be at any distance from him, or without his mind.  The objects to which he had hitherto been used to apply the terms up and down, high and low, were such only as affected or were some way perceived by his couch:  but the proper objects of vision make a new set of ideas, perfectly distinct and different from the former, and which can in no sort make themselves perceived by touch.  There is, therefore, nothing at all that could induce him to think those terms applicable to them:  nor would he ever think it till such time as he had observed their connexion with tangible objects, and the same prejudice began to insinuate itself into his understanding, which from their infancy had grown up in the understandings of other men.