Final answer:
The Keynesian model predicts that changes in the money supply will affect output in the short run, but they wil only affect prices in the long run.
Step-by-step explanation:
The Keynesian model predicts that in the short run, changes in the money supply will affect output, while in the long run, these changes will only affect prices. In the short run, when there is an increase in the money supply, it will lead to an increase in aggregate demand, which will stimulate output and increase employment.
On the other hand, a decrease in the money supply will have the opposite effect, leading to a decrease in output and employment. In the long run, however, the Keynesian model suggests that changes in the money supply will only affect prices.
This is because wages and prices are assumed to be flexible in the long run, and any changes in aggregate demand will be absorbed by changes in prices rather than output.