Three-sector model

The three-sector model in economics divides economies into three sectors of activity: extraction of raw materials (primary), manufacturing (secondary), and service industries which exist to facilitate the transport, distribution and sale of goods produced in the secondary sector (tertiary).[1] The model was developed by Allan Fisher,[2][3][4] Colin Clark,[5] and Jean Fourastié[6] in the first half of the 20th century, and is a representation of an industrial economy. It has been criticised as inappropriate as a representation of the economy in the 21st century.[7]

Industrial output in 2005
Service output in 2005

According to the three-sector model, the main focus of an economy's activity shifts from the primary, through the secondary and finally to the tertiary sector. Countries with a low per capita income are in an early state of development; the main part of their national income is achieved through production in the primary sector. Countries in a more advanced state of development, with a medium national income, generate their income mostly in the secondary sector. In highly developed countries with a high income, the tertiary sector dominates the total output of the economy.

The rise of the post-industrial economy in which an increasing proportion of economic activity is not directly related to physical goods has led some economists to expand the model by adding a fourth quaternary or fifth quinary sectors, while others have ceased to use the model.