Any temporally-quantized statistical operator characterizing a dynamic
ally isolated and localized non-relativistic quantum system which evol
ves strictly irreversibly can be approximated guile well for many purp
oses by one in which its intrinsic discrete overall time lapses are me
rely replaced by an appropriate single continuous temporal parameter.
Each such approximation differs very little from its original because
of a small total squared difference of the two which is found to exist
at all times. It is readily produced from any statistical operator wh
ich is a solution of the pertinent von Neuman's equation of motion. Th
e approximation satisfies a temporal differential equation similar in
some respects to that ascribed conventionally to a subsystem interacti
ng with the remainder of an otherwise isolated quantum system and to t
hat proposed recently imposing an intrinsic decoherence on the evoluti
onary behavior of such systems, but differs fundamentally from both. S
everal examples illustrate the applicability and limitations of the ap
proximation.