The spectroscopic factor has long played a central role in nuclear reaction theory. However, it is not an observable. Consequently it is of minimal use as a meeting point between theory and experiment. In this paper the nature of the problem is explo
red. At the many-body level, unitary transformations are constructed that vary the spectroscopic factors over the full range of allowed values. At the phenomenological level, field redefinitions play a similar role and the spectroscopic factor extracted from experiment depend more on the assumed energy dependence of the potentials than on the measured cross-sections. The consistency conditions, gauge invariance and Wegmanns theorem play a large role in these considerations.
The nature of the scientific method is controversial with claims that a single scientific method does not even exist. However the scientific method does exist. It is the building of logical and self consistent models to describe nature. The models ar
e constrained by past observations and judged by their ability to correctly predict new observations and interesting phenomena. The observations exist independent of the models but acquire meaning from their context within a model. Observations must be carefully done and reproducible to minimize errors. Models assumptions that do not lead to testable predictions are rejected as unnecessary.
