[…] Carnap has made it clear that what we take as ground elements [for a constitutional system] is a matter of choice. They are not dignified as the atomic units from which others must be built; they simply constitute one possible starting point. […] In choosing erlebs, Carnap is plainly seeking to approximate as closely as possible what he regards the original epistemological state […] Yet whether it does so or not is no test of the system. […] Hence […] argument concerning whether the elements selected are really primitive in knowledge is extraneous to the major purpose of the system. (SQ, 96–98)