text:  Had the eye been indicated to us in the mere act of seeing; had we become apprised of its existence _before_ we had associated our visual sensations with the tangible objects constituting the material universe the probability nay the certainty is that we would have associated them with this eye and that then it would have been as impossible for us to break up the association between colours and the organ as it now is for us to dissolve the union between colours and material things