"It is because of différance that the movement of
signification is possible only if each so-called "present" element,
each element appearing on the scene of presence, is related to
something other than itself, thereby keeping within itself the mark of
the past element, and already letting itself be vitiated by the mark
of its relation to the future element, this trace being related no
less to what is called the guture than to what is called the past, and
constituting what is called the present by means of this very relation
to what it is not: what it absolutely is not, not even a past or a
future as a modified present."
Jacques Derrida, "Différance"