The design of removable partial dentures has progressed both clinically and in laboratory research. Nonetheless, there still appears to be a conflict between the empirical practice and the scientific data available. On this basis, the authors question several aspects of the lingual connector. If lingual connectors are required to be rigid, how is this best achieved and can it be assured that designs impart sufficient rigidity? On the contrary, is it possible to make the connector too rigid? No conclusions are attempted in this theoretical discussion, but research to resolve the dilemma is encouraged.