  Bloom-Gilman duality demonstrates empirically that the electroproduction of
$N^*$'s at low momentum transfers averages smoothly around the scaling curve
measured at large momentum transfers. The latter is proportional to the sum of
the squares of the constituent charges whereas the former involves the coherent
excitation of resonances and is driven by the square of summed constituent
charges. We determine the minimal necessary conditions for this equality to be
realised so that duality can occur and consider the implications for a range of
processes that may be studied soon at CEBAF.
