  The impact of pionic correlations and meson--exchange currents in determining
the (vector) response functions for electroweak quasielastic lepton scattering
from nuclei is discussed. The approach taken builds on previous work where the
Fermi gas model is used to maintain consistency in treating forces and currents
(gauge invariance) and to provide a Lorentz covariant framework. Results
obtained in first-order perturbation theory are compared with infinite-order
summation schemes (HF and RPA) and found to provide quite successful
approximations for the quasielastic response functions. The role of pionic
correlations in hardening the responses R_L and R_T is investigated in some
detail, including studies of the relative importance of central and tensor
pieces of the force and of exchange and self-energy diagrams; in addition,
their role in significantly modifying the longitudinal parity-violating
response R_{AV}^L is explored. The MEC are shown to provide a small, but
non-negligible, contribution in determining the vector responses.
