  I argue that, contrary to the standard view, one cannot understand the
structure and nature of our knowledge in physics without an analysis of the way
that observers (and, more generally, measuring instruments and experimental
arrangements) are modeled in theory. One upshot is that standard pictures of
what a scientific theory can be are grossly inadequate. In particular, standard
formulations assume, with no argument ever given, that it is possible to make a
clean separation between, on the one hand, one part of the scientific knowledge
a physical theory embodies, viz., that encoded in the pure mathematical
formalism and, on the other, the remainder of that knowledge. The remainder
includes at a minimum what is encoded in the practice of modeling particular
systems, of performing experiments, of bringing the results of theory and
experiment into mutually fruitful contact---in sum, real application of the
theory in actual scientific practice. This assumption comes out most clearly in
the picture of semantics that naturally accompanies the standard view of
theories: semantics is fixed by ontology's shining City on the Hill, and all
epistemology and methodology and other practical issues and considerations are
segregated to the ghetto of the theory's pragmatics. We should not assume such
a clean separation is possible without an argument, and, indeed, I offer many
arguments that such a separation is not feasible. An adequate semantics for
theories cannot be founded on ontology, but rather on epistemology and
methodology.
