The concept of labor is the strong foundation in Marx's theory of labor value,the duality of labor is very important to Marx's theory.However,the"foundation stone"of his labor theory is only an inheritance of the metaphysical understanding of"things"since modern times.Marx packages this understanding of"things"into the concept of labor,giving the concept of labor a"solidity"character.Looking back on the criticism of Senior's"last hour"theory in Capital,inspired by Mar's criticism,it is found that the concept of"concrete labor"actually contains an abstract"thing",and this is the metaphysical premise that Marx had not been conscious of in his labor theory of value,that is,he identified"solid"labor based on"things".