The debate over the appropriate level for a central bank’s inflation objective reminds us of a 40-year-old Sherlock Holmes movie called “The Seven-Per-Cent Solution.” Convinced that Holmes’ addiction to cocaine (the solution in the title) had made him delusional, Watson took the master sleuth to Vienna to be treated by Sigmund Freud.

Has the 2% solution for inflation targeting in advanced economies made central bankers similarly delusional? Are they stubbornly attached to an outdated target? That argument gained ground in recent years as policymakers in Europe, Japan, and the United States struggled to stimulate weak economies and stabilize prices with policy interest rates stuck at the zero bound...