The suggestion by several authors that the solar differential rotation
is caused by a large scale instability of the basic convective state
is examined. We find that the proposed mean-field models are unstable
to a Rayleigh-Benard type instability, but argue that this cannot expl
ain the differential rotation of the Sun, because such a flow would be
come nonaxisymmetric. We discuss the applicability of the mean-field e
quations to the problem.