Marx agreed that workers employed in circulation (e.g., in marketing) do not produce value (otherwise he would have to concede that value could be produced by market exchange). They can, however, be a source of surplus value. They are like machines which cannot produce value but whose use can increase relative surplus value by lowering the costs of wage goods and so diminishing the value of labour power thereby producing more surplus value for the capitalist. Costs entailed in circulation and state administration, Marx argued, should be viewed as deductions out of value and surplus value production. Costs of circulation in the market (other than those of transportation), no matter whether borne by the industrial or merchant capitalist, are considered as necessary deductions from potential value already produced. [...]