  We find that the electric field is not a suitable physical quantity to
describe the response of a non-metallic material in the study of non-resonant
near-field optics. In practice, we show the spin-less one-electron two-level
system responds differently to longitudinal and transverse electric fields
under the non-resonant condition. This difference originates from the
non-relativistic nature of the system, and should exist in actual many-electron
systems. For this type of system, it is a logical fallacy to use the
constitutive equation in terms of the total electric field and the associated
permittivity. Recognizing this fallacy, both experimental and theoretical
progress is needed in the field of non-resonant near-field optics of
non-metallic materials.
