 Additionally, there is another potential problem that arises from thinking about the faithful model assumption, namely what is the relationship or mapping between model and target system? Is it one-to-one as we standardly assume? Or is it a one-to-many relation (several different nonlinear models of the same target system or, potentially, vice versa) or a many-to-many  relationship?[5] For many classical mechanics problems—namely, where linear models or force functions are used in Newton’s second law—the mapping or translation between model and target system appears to be straightforwardly one-to-one. However, in nonlinear contexts, where one might be constructing a model from a data set generated by observing a system, there are potentially many nonlinear models that can be constructed, where each model is as empirically adequate to the system behavior as any other. Is there really only one unique model for each target system and we simply do not know which is the “true” one (say, because of underdeterminiation problems—see  scientific realism)?  Or is there really no one-to-one relationship between our mathematical models and target systems? 