Q. Describe Keynesian cross model?

Keynesian cross model is a simple version of what we call the 'complete Keynesian model' or simply the Keynesian model. Keynesian model has as its origin the writings of John Maynard Keynes in the 1930s, specifically the book 'The general theory of Employment, Interest, and Money'. Though this book was written as a criticism of the classical model, similarities between Keynesian model and classical model are definitely greater than the differences. Let's point out the three most significant differences directly: 

• Say's Law doesn't apply in the Keynesian model.
• the quantity theory of money doesn't apply in the Keynesian model.
• the nominal wage level W is an exogenous variable in Keynesian model.

Remember that W being exogenous means that it's pre-determined outside the model. It doesn't necessarily mean that it's constant over time - even though this is a common assumption. Though the nominal wage should be known at any point in time in this model. To simplify our description of Keynesian model, we will begin by presuming that W is constant.