The long-run Phillips curve becomes almost vertical at the natural rate of unemployment. 12. Of course, there is a possibility of lengthening the short-run ‘trade-offs’ indefinitely, since inflation surprises in each period can elongate the long-run perpetually. But, in that case the ‘trade-offs’ will become sharper in each successive period.
In other words, to maintain the unemployment below the ‘natural’ rate, policy authorities will have to inflate the economy at higher rates in each successive period. This has a major policy implication even if the economy does not operate on the long-run vertical Phillips curve.