  In this paper we study QCD and power corrections to sum rules which show up
in deep inelastic lepton-hadron scattering. Furthermore we will make a
distinction between fundamental sum rules which can be derived from quantum
field theory and those which are of a phenomenological origin. Using current
algebra techniques the fundamental sum rules can be expressed into expectation
values of (partially) conserved (axial-) vector currents sandwiched between
hadronic states. These expectation values yield the quantum numbers of the
corresponding hadron which are determined by the underlying flavour group
$SU(n)_F$. In this case one can show that there exist an intimate relation
between the appearance of power and QCD corrections. The above features do not
hold for phenomenological sum rules, hereafter called non-fundamental. They
have no foundation in quantum field theory and they mostly depend on certain
assumptions made for the structure functions like superconvergence relations or
the parton model. Therefore only the fundamental sum rules provide us with a
stringent test of QCD.
