Between the ideal and the sensible Plato interposes the two
natures of time and space. Time is conceived by him to be only
the shadow or image of eternity which ever is and never has been
or will be, but is described in a figure only as past or future.
This is one of the great thoughts of early philosophy, which are
still as difficult to our minds as they were to the early
thinkers; or perhaps more difficult, because we more distinctly
see the consequences which are involved in such an hypothesis.
All the objections which may be urged against Kant’s doctrine of
the ideality of space and time at once press upon us. If time is
unreal, then all which is contained in time is unreal—the
succession of human thoughts as well as the flux of sensations;
there is no connecting link between (Greek) and (Greek). Yet, on
the other hand, we are conscious that knowledge is independent of
time, that truth is not a thing of yesterday or tomorrow, but an
‘eternal now.’ To the ‘spectator of all time and all existence’
the universe remains at rest. The truths of geometry and
arithmetic in all their combinations are always the same. The
generations of men, like the leaves of the forest, come and go,
but the mathematical laws by which the world is governed remain,
and seem as if they could never change. The ever-present image of
space is transferred to time—succession is conceived as
extension. (We remark that Plato does away with the above and
below in space, as he has done away with the absolute existence
of past and future.) The course of time, unless regularly marked
by divisions of number, partakes of the indefiniteness of the
Heraclitean flux. By such reflections we may conceive the Greek
to have attained the metaphysical conception of eternity, which
to the Hebrew was gained by meditation on the Divine Being. No
one saw that this objective was really a subjective, and involved
the subjectivity of all knowledge. ‘Non in tempore sed cum
tempore finxit Deus mundum,’ says St. Augustine, repeating a
thought derived from the Timaeus, but apparently unconscious of
the results to which his doctrine would have led.