In the Blanchard/New Consensus model, the PS line shifts due to changes in costs and productivity; in the alternative model, the PS line can shift due to changes in costs and productivity, too, but also by changes in demand." Explain.

 "In the Blanchard/New Consensus model, labor costs change when W changes; in the alternative model, labor costs are considered as a total "bill" composed of W, jobs, and hours, any of which may be changed."