  We present an analysis of the role of the running coupling constant at the
intersection of perturbative and nonperturbative QCD in the context of the
quark-hadron duality \`a la Bloom-Gilman. Our framework will be the unpolarized
structure function of the proton in the resonance region. We suggest that the
realization of duality is related to the inclusion of nonperturbative effects
at the level of the coupling constant. The outcome of our analysis is a smooth
transition from perturbative to nonperturbative QCD physics, embodied in the
running of the coupling constant at intermediate scales.
