The state of being without any work yet looking for work is called unemployment. Economists distinguish between various overlapping types of and theories of unemployment, including cyclical or Keynesian unemployment, frictional unemployment, structural unemployment and classical unemployment. Some additional types of unemployment that are occasionally mentioned are seasonal unemployment, hardcore unemployment, and hidden unemployment. Though there have been several definitions of "voluntary" and "involuntary unemployment" in the economics literature, a simple distinction is often applied. Voluntary unemployment is attributed to the individual's decisions, but involuntary unemployment exists because of the socio-economic environment (including the market structure, government intervention, and the level of aggregate demand) in which individuals operate. In these terms, much or most of the frictional unemployment is voluntary since it reflects individual search behavior. Voluntary unemployment includes workers who reject low-wage jobs, but involuntary unemployment includes workers fired because of an economic crisis, industrial decline, company bankruptcy, or organizational restructuring. On the other hand, cyclical unemployment, structural unemployment, and classical unemployment are largely involuntary in nature. However, the existence of structural unemployment may reflect choices made by the unemployed in the past, and classical (natural) unemployment may result from the legislative and economic choices made by labor unions or political parties. The clearest cases of involuntary unemployment are those with fewer job vacancies than unemployed workers even when wages are allowed to adjust and so even if all vacancies were to be filled, some unemployed workers would still remain. That happens with cyclical unemployment, as macroeconomic forces cause microeconomic unemployment, which can boomerang back and exacerbate those macroeconomic forces.