Why would an economist choose either the neoclassical perspective or the Keynesian perspective, but not both? Why would an economist choose either the neoclassical perspective or the Keynesian perspective, but not both?

This is because the concepts and approaches to economic issues differ.

Explanation:

Too begin with, it is important to understand the concept of neoclassical perspective and Keynesian perspective.

Neoclassical perspective hinges on the fact that demand and supply as the Filip behind production, pricing, productivity and consumption pattern of end users and thus a factor towards economic growth and productivity. It simply allows for market forces to interplay.

Keynesian perspective, on the other hand, hinges on the fact that the demand is the singular factor behind economic growth and prosperity. Thus, an economy driving towards growth and development should increase its aggregate demand.

In effect, and going by the above definitions, an economist will thus only choose one simply because the two perspectives differ in approach and concepts.

While one considers both aggregate demand and aggregate supply as a tool towards economic growth and prosperity, the other is strictly conservational, and believes the authority should stimulate only aggregate demand as a tool towards economic growth and development.