  The use of weak decays to determine proton spin structure is examined in view
of possible violations of the Bjorken and Gottfried Sum rules, flavor symmetry
breaking and flavor asymmetry in the sea. The use of the neutron decay is found
to be unaffected by all these. A method for including these effects in analyses
of hyperon decays shows that a flavor-asymmetric sea produced by SU(3) symmetry
breaking has only a small effect on results for the total spin carried by
quarks. However the strange quark contribution cannot be reliably obtained from
charged lepton scattering and weak decay data alone, and requires additional
model-dependent input relating nucleon and hyperon wave functions.
