Editing Operational definition (section)

=== Philosophy ===
The ''Stanford Encyclopedia of Philosophy'' entry on scientific realism, written by [[Richard Boyd]], indicates that the modern concept owes its origin in part to [[Percy Williams Bridgman]], who felt that the expression of scientific concepts was often abstract and unclear. Inspired by [[Ernst Mach]], in 1914 Bridgman attempted to redefine unobservable entities concretely in terms of the physical and mental operations used to measure them.<ref name=Boyd>{{cite encyclopedia|last=Boyd|first=Richard|title=Scientific Realism|url=https://plato.stanford.edu/archives/sum2010/entries/scientific-realism/|encyclopedia=Stanford Encyclopedia of Philosophy|access-date=8 February 2013}}</ref> Accordingly, the definition of each unobservable entity was uniquely identified with the instrumentation used to define it. From the beginning objections were raised to this approach, in large part around the inflexibility. As Boyd notes, "In actual, and apparently reliable, scientific practice, changes in the instrumentation associated with theoretical terms are routine.  and apparently crucial to the progress of science. According to a 'pure' operationalist conception, these sorts of modifications would not be methodologically acceptable, since ''each'' definition must be considered to identify a ''unique'' 'object' (or class of objects)."<ref name=Boyd />