  We study the Aharonov-Casher (AC) effect and the related He-McKellar-Wilkens
(HMW) effect in 2+1 dimensions. In this restricted space these effects are the
result of the interaction of the electromagnetic field tensor with the dual of
a current. Transferring the dual operation from the current to the field tensor
shows that this interaction may be reinterpreted as due to the interaction of
an effective vector potential and a current, and the AC and HMW effects follow
immediately. A general proof of this for particles with an arbitrary spin is
provided.
  The restriction to 2+1 dimensions, with this interpretation, provides a
unified way of treating the AC and HMW effects for an arbitrary spin. Perhaps
more interestingly the treatment shows that a spin-0 particle can show AC and
HMW effects, although it has no magnetic or electric dipole moment in the usual
sense.
