The main reason why the long - run Phillips curve may have a negative slope is that workers may continue to suffer from money illusion in the long - run and so be prepared to accept money wage increases which fall short of the actual inflation rate.
The main reason why the long - run Phillips curve may have a negative slope is that workers may continue to suffer from money illusion over a long period of time and so be prepared to accept money wage increases which fall short of the actual inflation rate.