"Commodities can provisionally be defined as objects of economic value." (Arjun Appadurai, "Commodities and the politics of value," in The Social Life of Things, p 3)This economic value, following Simmel, is defined as a reciprocal formation in the possibilities of exchange. "The sacrifice or renunciation that is interposed between man and the object of his demand is, at the same time, the object of someone else's demand. The one has to give up possession or enjoyment that the other wants in order to persuade the latter to give up what he owns and the former wants." (The Philosophy of Money, p 78) Thus, rather than looking for some characteristic of the commodity itself as its defining characteristic, Appadurai argues that commodities should be look at as "things in motion" in order to illuminate their human and social context. He defines the "commodity situation in the social life of any "thing" the situation in which its exchangibility (past, present, or future) for some other thing is its socially relevant feature." (p.13) These exchanges take place within specific "regimes of value," and may only be one phase in the "life history" of an object. 

Karl Marx describes the fetish quality of commodities as a misplacement, projection, or reification. "It is nothing but the definite social relation between men themselves which assumes here, for them, the fantastic form of a relation between things." (Capital, Chapt 1, sect. 4)