Sir William Arthur Lewis (23 January 1915 – 15 June 1991) was a Saint Lucian economist and the James Madison Professor of Political Economy at Princeton University.

[7] After finishing school when he was 14 years old, Lewis worked as a clerk, while waiting to be old enough to sit the examination for a government scholarship to a British university, which would be in 1932.

"[6] At the age of 18, he earned the government scholarship to attend the London School of Economics (LSE), becoming the first black individual to gain acceptance there.

While enrolled to study for a Bachelor of Commerce degree ("which offered accounting, business management, commercial law and a little economics and statistics") in 1933,[6] he would achieve similar success as he did at grade school.

After Lewis graduated in 1937 with first-class honours, LSE gave him a scholarship to read for a PhD in industrial economics,[6] under the supervision of Arnold Plant.

[13][citation needed] Lewis served as an economic advisor to numerous African and Caribbean governments, including Nigeria, Ghana, Trinidad and Tobago, Jamaica, and Barbados.

When Ghana (where in 1929 his eldest brother Stanley had settled)[14] gained independence in 1957, Lewis was appointed as the country's first economic advisor.

[22] Lewis is now characterised as "among the earliest proponents of Reparations for the former West Indies for Britain's colonial wrongs" because of the ideas he put forward in this work.

The subsistence sector is governed by informal institutions and social norms so that producers do not maximize profits and workers can be paid above their marginal product.

At an early stage of development, the "unlimited" supply of labour from the subsistence economy means that the capitalist sector can expand for some time without the need to raise wages.

Given the assumptions of the model (for example, that the profits are reinvested and that capital accumulation does not substitute for skilled labour in production), the process becomes self-sustaining and leads to modernization and economic development.

[28] Work building on Lewis's analysis has shown that productivity gains in the areas formerly occupied by the subsistence sector (e.g. agriculture) can offset some of the labour demand.