Two basic types of dephasing mechanisms, carrier-carrier and carrier-phonon scattering including hole-hole and hole-phonon scattering are proposed in the theory of ultrafast polarization dephasing of continuum transitions in bulk semiconductors. The contribution of optical phonon scattering to the dephasing rate is the average of the scattering rates for electrons and holes. A weighting factor that reflects the change in the momentum of the particle in a collision is introduced into the usual integral of the carrier-carrier scattering rate to describe the contribution of carrier-carrier scattering to the dephasing rate for the case of static screening interaction. The theoretical calculations are in quantitative agreement with the reported experimental results.