In the best known treatment of it, it was presented as an obstacle to equality because, in order to live as a person who uses it for their income, they must live upon the labor of another, eventually killing them; in response to the titular question asking what it is, that work proclaims that it is theft.  
In The Commonwealth of Oceana, Robert Harrington argued that this concept was the basis for the power of a state.  The largest section of William Blackstone's Commentaries on the Laws of England deals with it, and Charles Comte wrote about the "theory of" it in an attempt to maintain it in the wake of the July Revolution.  Frederic Bastiat defined it as a form of value that can be traded away, and not as a physical object.  In The Mystery of Capital, Hernando de Soto outlined the need for (*) rights to this concept as a necessity for developing economies.  In the best known treatment of it, it was presented as an obstacle to equality because, in order to live as a person who uses it for their income, they must live upon the labor of another, eventually killing them; in response to the titular question asking what it is, that work proclaims that it is theft.  For 10 points, name this concept discussed by Pierre-Joseph Proudhon, defined as something that is owned by someone.
In The Commonwealth of Oceana, Robert Harrington argued that this concept was the basis for the power of a state.  
{property}