This document discusses the relationship between the aggregate expenditure (AE) model and the aggregate demand (AD) curve. It explains that a change in AE due to price changes leads to a movement along the fixed AD curve, while a non-price change in AE causes the AD curve to shift. It also shows graphs depicting how an increase in the price level reduces AE and GDP, represented as a downward shift of the AD curve. Finally, it illustrates that any non-price change in AE, such as an investment increase, results in an upward shift of both the AE curve and the AD curve, raising equilibrium GDP.