vertex functions are not unique. We argue generally and with two explicit examples that while the propagator depends on the choice of field variables, the observables do not. Thus, knowledge of the off-shell meson propagator by itself gives no information unless one knows which field is used. One may be able to deduce which definition of the field has been used from a complete theory by studying the interactions with the other degrees of freedom in the problem. However, if the theory is incomplete and the interactions of the field with all of the other degrees of freedom is unknown, knowledge of the off-shell propagator by itself is not physically meaningful.

There is an even more serious problem. Modern meson exchange potentials are motivated by field theoretic concerns. However, there is no first principle method for obtaining the “correct” NN potential directly from either QCD, or from some hadron field theoretic model or from any experimentally accessible set of data of hadronic properties. Given this essential difficulty, we believe it is sensible to adopt the general approach used in the construction of meson exchange potentials to the case of charge symmetry breaking. This approach makes the pragmatic assumptions of including 