We must now examine the type of exploitation which arises because the supply of labour is imperfectly elastic to the unit of control. The supply to an industry may be less than perfectly elastic for any of the reasons discussed in Chapter 8. The nature of the limitation upon the supply of labour is not relevant to our inquiry, for our analysis can be applied to limitations of any type, but for the sake of simplicity we will first deal only with one case: that in which all the workers employed are alike in their efficiency in the industry in question, and yet progressively higher wages have to be paid to all in order to attract fresh supplies of labour. This might occur because it was necessary to tempt labour away from better paid occupations, to overcome the cost of movement from more distant regions, or to overcome a preference for other occupations.