Semileptonic<i>B</i>and<i>D</i>decays in the quark model

We predict the matrix elements and resulting electron spectra for semileptonic meson decays using the quark potential model. Particular attention is paid to the high-energy electron end-point region in B decay since it is crucial to a determination of the b\ensuremath{\rightarrow}u weak mixing angle. It is argued that in this region the usual inclusive (``quark decay'') calculations are unjustified and must be replaced by explicit sums over decays of the original meson into low-mass exclusive hadronic final states.