_The perception of a past event as in process of occurring, or the
prevision of something which comes to pass later_.
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.