  We present a simple method to count the number of hadronic form factors based
on the partial wave formalism and crossing symmetry. In particular, we show
that the number of independent nucleon form factors of spin-n, twist-2
operators (the vector current and energy-momentum tensor being special
examples) is n+1. These generalized form factors define the generalized
(off-forward) parton distributions that have been studied extensively in the
recent literature. In proving this result, we also show how the J^{PC} rules
for onium states arise in the helicity formalism.
