  We consider social learning in a changing world. Society can remain
responsive to state changes only if agents regularly act upon fresh
information, which limits the value of social learning. When the state is close
to persistent, a consensus whereby most agents choose the same action typically
emerges. The consensus action is not perfectly correlated with the state
though, because the society exhibits inertia following state changes. Phases of
inertia may be longer when signals are more precise, even if agents draw large
samples of past actions, as actions then become too correlated within samples,
thereby reducing informativeness and welfare.
