But, aggregate demand is only half of the view of the economy that we have been building up to in macroeconomics. The other half of this view, aggregate supply, was covered in the following SparkNote on Aggregate Supply . For now, we will focus on the basics of aggregate demand. We will work through why the aggregate demand curve is downward sloping. We will also catch a glimpse of how the aggregate demand curve is derived. Finally, we will see how the aggregate demand curve shifts when economic variables change the aggregate demand.