Justin Fox at Bloomberg on Carroll D. Wright in the 1870s:
As David Leonhardt explained in a great New York Times column in 2008, this all started in the U.S. with Carroll D. Wright, who as head of the Massachusetts Bureau of the Statistics of Labor during the economic hard times of the 1870s set out to measure joblessness while excluding people he considered malingerers:
The survey asked town assessors to estimate the number of local people out of work. Wright, however, added a crucial qualification. He wanted the assessors to count only adult men who “really want employment,” according to the historian Alexander Keyssar. By doing this, Wright said he understood that he was excluding a large number of men who would have liked to work if they could have found a job that paid as much as they had been earning before.Wright went on to become the first commissioner of what is now the BLS.
...if they could have found a job that paid as much as they had been earning before.
Maynard Keynes in 1936:
If, indeed, it were true that the existing real wage is a minimum below which more labour than is now employed will not be forthcoming in any circumstances, involuntary unemployment, apart from frictional unemployment, would be non-existent. But to suppose that this is invariably the case would be absurd.
... if they could find a job that paid less, they would take it. They wouldn't prefer it, but if nothing else was available...
Scott Sumner in 2015:
I think they were unemployed because of sticky wages, and that if workers collectively accepted lower wages then we would have had full employment in 1936.
... they refused to work for less...