Q. Describe about consumption function?

The consumption function

Aggregate demand for consumer goods is stated as total amount of finished services and goods that households wish to buy under different conditions. There is not any specific supply of consumer goods - firms offer final goods however do not distinguish between supply to consumers, supply to investors and supply to foreigners. 

We have used the symbol C for observed consumption. To be consistent with the notation we must denote the demand for consumer goods by C_D. Though this isn't common practice in macroeconomics. In its place symbol C is used for the demand for consumer goods as well. Luckily, it's almost always obvious from the context if symbol C represents the observed consumption - it's then a variable - and when C signifies the demand for consumer goods - it is then a function. 

Furthermore, the term 'demand for consumer goods' is frequently shortened to the 'demand for consumption' or simply 'consumption'. Whenever you see 'consumption', you need to figure out if it means observed consumption or consumption demand. 

In the classical model, demand for consumption is presumed to be negatively related to real interest rate r. higher real interest rates makes it more expensive to borrow money for consumption today. In the same way, it will be more favourable to postpone consumption to the future.  

Consumption is hence denoted by C(r) and this notation makes it clear that we are talking about demand for consumption and not observed consumption.