This chapter focuses on growth as a continuous process and understands the concepts of exponential functions and natural logarithms. The term 'exponential function' is usually used to describe the specific natural exponential function. In mathematics there is a special number which yields several useful results when used as a base for an exponential function and is usually represented by the letter 'e'. In economics, exponential functions to the base e are particularly useful for analysing growth rates. Logarithms to the base e have several useful properties and applications in mathematics. These are known as 'natural logarithms', and the usual notation is 'ln'. In a basic Keynesian macroeconomic model, with no foreign trade and no government sector, total expenditure will be the sum of consumer expenditure and exogenously determined investment.