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A new method to extract |V bc | is proposed based on a sum–rule for semilep-tonic decays of the B meson. The method relies on much weaker assumptions than previous approaches which are based on heavy–quark symmetry. This sum–rule only relies on the assumption that the virtual cc pair content of the B meson can be neglected. The extraction of the CKM matrix element also requires that the sum–rule saturates in the kinematically accessible region. is one of the fundamental parameters of the standard model. Direct measurements of this matrix element at the quark level are not possible because the quarks are confined in hadrons. Thus, to extract V bc from experimental measurements it is necessary to understand the strong interactions well enough to relate the observables, which involve hadrons, to the underlying quark dynamics. In principle, if one knew the exact quantum state for an initial hadron containing a b quark and an exact quantum final state containing a c quark, one could extract the magnitude of V bc from a weak decay from the initial " b " hadron to the final state. Until recently it was believed that until reliable ab initio calculations were available directly from QCD via lattice simulations, one was unadvoidabley forced to rely on low energy models for the hadronic matrix elements. However, as was noted by Nussinov and Wetzel [1] and by Isgur and Wise [2], if the assumptions underlying heavy quark symmetry are valid, there is a model independent way to extract |V bc | from exclusive semi-leptonic weak decays of the B meson into a D or D * meson; analogously, semi-leptonic decays of the Λ b into Λ c could be used. An alternative method to extract V bc from semi-leptonic decays has been proposed by Bjorken, Dunietz and Tarron (BDT) [3]. The BDT method also depends on the validity of the assumptions underlying heavy quark symmetry; if valid, BDT show that inclusive B meson or Λ b semi-leptonic decays into charmed states at fixed three momentum satisfy a sum-rule. In fact, this sum rule basically just reproduces the spectator model, and hence by experimentally measuring the semi-leptonic partial width, one directly extracts |V bc |. In the present letter we observe, there exists a sum-rule for semi-leptonic B or Λ b decays similar in spirit to BDT but with much weaker assumptions. In particular, the only assumption we …