  The analyzability of the universe into subsystems requires a concept of the
"independence" of the subsystems, of which the relativistic quantum world
supports many distinct notions which either coincide or are trivial in the
classical setting. The multitude of such notions and the complex relations
between them will only be adumbrated here. The emphasis of the discussion is
placed upon the warrant for and the consequences of a particular notion of
subsystem independence, which, it is proposed, should be viewed as primary and,
it is argued, provides a reasonable framework within which to sensibly speak of
relativistic quantum subsystems.
