  Sum rules based upon heavy quark effective theory indicate that the
Isgur-Wise function $\xi(w)$ has a minimum slope as w approaches 1, which is
zero for light degrees of freedom with zero spin and 1/4 for light spin 1/2.
Quark-model studies reveal sources for a minimum slope from a variety of
relativistic effects. In this paper the origins of the minimum slope in the
sum-rule and quark-model approaches are compared by considering hadrons with
arbitrary light spin. In both approaches the minimum slope increases with the
light spin, but there appears to be no detailed correspondence between the
quark-model and sum-rule approaches.
