State law of diminishing returns to a factor. 

Statement of law. The law of diminishing return to a factor states, 'If we keep increasing the employment of variable input, with other inputs fixed, eventually a point will be reached after which the resulting addition to output (i.e. marginal product) of that input will start falling'. In fact, only Classical economists treated it as a separate law which applies in the field of agriculture but modern economists apply it in every field of production. They treat this law just one aspect (aspect of diminishing returns) of law of variable proportions.