  There is a deeply entrenched view in philosophy and physics, the closed
systems view, according to which isolated systems are conceived of as
fundamental. On this view, when a system is under the influence of its
environment this is described in terms of a coupling between it and a separate
system which taken together are isolated. We argue against this view, and in
favor of the alternative open systems view, for which systems interacting with
their environment are conceived of as fundamental, and the environment's
influence is represented via the dynamical equations that govern the system's
evolution. Taking quantum theories of closed and open systems as our case
study, and considering three alternative notions of fundamentality: (i)~ontic
fundamentality, (ii)~epistemic fundamentality, and (iii)~explanatory
fundamentality, we argue that the open systems view is fundamental, and that
this has important implications for the philosophy of physics, the philosophy
of science, and for metaphysics.
