An important notion in Mauss' conceptualisation of gift exchange is what Gregory (1982, 1997) refers to as "inalienability". In a commodity economy, there is a strong distinction between objects and persons through the notion of private property. Objects are sold, meaning that the ownership rights are fully transferred to the new owner. The object has thereby become "alienated" from its original owner. In a gift economy, however, the objects that are given are inalienated from the givers; they are "loaned rather than sold and ceded". It is the fact that the identity of the giver is invariably bound up with the object given that causes the gift to have a power which compels the recipient to reciprocate. Because gifts are inalienable they must be returned; the act of giving creates a gift-debt that has to be repaid. Because of this, the notion of an expected return of the gift creates a relationship over time between two individuals. In other words, through gift-giving, a social bond evolves that is assumed to continue through space and time until the future moment of exchange. Gift exchange therefore leads to a mutual interdependence between giver and receiver. According to Mauss, the "free" gift that is not returned is a contradiction because it cannot create social ties. Following the Durkheimian quest for understanding social cohesion through the concept of solidarity, Mauss' argument is that solidarity is achieved through the social bonds created by gift exchange. Mauss emphasizes that exchanging gifts resulted from the will of attaching other people'to put people under obligations', because "in theory such gifts are voluntary, but in fact they are given and repaid under obligation".