Following some observations of Howard Stein, I argue that, contrary to
contemporary standard philosophical views of physical theories, 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 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, \emph{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 segregation is possible without an
argument, and, indeed, I offer many arguments that such a segregation is
not feasible. It follows that an adequate semantics for theories cannot
be founded on ontology, but rather on epistemology and methodology. I
develop and marshall my arguments based on an attempt at a fundamental
reorentiation away from the standard view of a theory: I propose that it
is more fruitful to conceive of a theory as an integral body of
knowledge rather than as a formal system in conjunction with procedures
for bringing the formalism into contact with empirical data or experience.