Many of the jobs that existed before the recession (in home building, for example) are gone for good, and the people who held those jobs don’t have the skills needed to work in other fields. A big chunk of current unemployment, the argument goes, is therefore structural, not cyclical: resurgent demand won’t make it go away. Though this may sound like an academic argument, its consequences are all too real. If the problem is a lack of demand, policies that boost demand—fiscal stimulus, aggressive monetary policy—will help. But if unemployment is mainly structural there’s little we can do about it.