Some economicists such as Paul Samuelson have taken issue with Marx's concept of the reserve army of labour. Samuelson argues that much Marxian literature assumes that the mere existence of the unemployed drives down wages, when in reality is dependent upon contingent factors (Are the unemployed easily available as replacements? Is the mere threat of replacement sufficient to get workers to accept a wage cut or does the employer have to demonstrate this is not an empty threat?).