Kirchhoff’s diffraction theory is introduced as a new case study in the realism debate. The theory is extremely successful despite being both inconsistent and not even approximately true. Some habitual realist proclamations simply cannot be maintained in the face of Kirchhoff’s theory, as the realist is forced to acknowledge that theoretical success can in some circumstances be explained in terms other than truth. The idiosyncrasy (or otherwise) of Kirchhoff’s case is considered.