The theoretical definition of partial ionic character is considered. The basic requirements which the author feels must be met before a satisfactory theoretical definition can be found are outlined. It is shown that current models for defining partial ionic character fall short of meeting these criteria. Suggestions are made as to the directions in which one must look for better models. In particular, it is emphasized that the dual requirements of orthogonal concepts based upon models which are invariant to arbitrary choices of basis functions must be met.