In the three-sector theory of economics, the business sector is divided into three types: the primary sector of raw materials, the secondary sector of manufacturing, and the tertiary sector of sales and services. Additionally, some modern theories further elaborate upon the tertiary sector, creating from it a quaternary sector that pertains to information services and a quinary sector related to scientific and cultural advancement.
In economics, the business sector is the portion of the economy that consists of for-profit companies. The economic theories of Jean Fourastie and Colin Clark rank the types of business sectors in order of their level of economic advancement.
The theory argues that, as it develops industrially, greater portions of a society's population are employed in the secondary sector instead of the first. This results in generally higher per-capita incomes and a higher qualities of life. In the United States and Europe, this process was demonstrated by the Industrial Revolution.
Societies that later progress into post-industrial economies gradually experience a similar population shift into the tertiary sector, which requires higher levels of education and opportunity. Thus, the private and public wealth seen in post-industrial societies is largely generated from the sale of finished products and services.