It might be, although it is not probable, that what appears green to me and what I call green, may appear different to other people, perhaps gray, red, or brown, or some other color that I know not of: yet other people will—just as much as I do—call that peculiar sensation green which they experience under the same conditions, for instance, when seeing the fresh leaves of a tree. It is quite indifferent how variegated in single minds the feelings may be that accompany each kind of sensation. So long as they have for every special objective state a special analogue, they can map out in their minds their surroundings, they can have a correct representation of the world, and so long as they employ the same symbols (words or other signs) for indicating the same objective states, it is quite indifferent whether or not the feelings that are produced in the process of observation vary. It would make no more difference for the general purpose of mental operations, than it would if we were to employ Roman letters, or Italics, or Greek or Hebrew characters to designate the lines and points in explaining a mathematical figure. The main thing is that certain points are marked and represented by some sign which stands for this or that point and for that alone. To cite another example in illustration of the subjective element of feeling in cognition, we may compare our knowledge of the world to the map of a city. The map may be printed in black, green, red, blue, or any other color. The color in which the map is printed represents the subjective element of feeling, while the form of the lines, their geometrical configuration, contains the objective element of the things represented. The map is good, i. e. its representations are true, if the squares and the streets of the city stand in the same relation among each other, as the little blocks and divisions on the map do. Whether the map is printed in green or blue will make no difference so long as we find everything we want to know about the city represented in a way such that we should be able to set ourselves aright and to find our bearings if we went astray. The subjective element in mind is not of one half the importance generally attributed to it. The objective element, being that which is represented, is paramount, and it is the aspiration of all the sciences to concentrate their entire attention upon the objective features of observation. Objective truth is what we want, and objective truth is identical with a scientific description of facts. * * * * * What then is the criterion of objective truth for the interpretation of facts? Is it not wanting? May it not be that a person, Mr. A., will under given circumstances regularly see a ghost. Indeed we do not doubt that he will, and we can even prove it by experiment. This being so, is not the interpretation of facts as to whether the phenomenon is a real ghost or a mere vision, beyond any criterion of truth?