No mechanistic explanation will serve to account for this order of clairvoyance since it is inextricably involved in the mystery of consciousness itself. Yet our already overworked analogy can perhaps cast a little light even here.
To the flat-man, the third dimension of objects passing through his plane translates itself to his experience into time. Were he capable of rising in the positive direction of the third dimension, he would have pre-vision, because he would be cognizant of that which had not yet intersected his plane: by sinking in the negative direction, he would have post-vision, because he could re-cognize that which had already passed.
Now there are excellent reasons, other than those based on analogy, that the fourth-dimensional aspect of things may manifest itself to our ordinary experience, not as spatial extension, but as temporal change. Then, if we conceive of clairvoyance as a transcending by consciousness of our three-dimensional space, prevision and post-vision would be logically possible as corresponding to the positive and negative of the fourth dimension. This may be made clearer by the aid of a homely illustration.
PISGAH SIGHTS OF LIFE'S PAGEANT
Suppose you are standing on a street corner, watching a procession pass. You see the pageant as a sequence of objects and individuals appearing into view near by and suddenly, and disappearing in the same manner. This would represent our ordinary waking consciousness of what goes on in the world round about. Now imagine that you walk up the street in a direction opposite to that in which the procession is moving. You then rapidly pass in review a portion of the procession which had not yet arrived at the point you were a few moments before. This would correspond to the seeing of something before it "happened," and would represent the positive aspect of clairvoyance in time—prevision. Were