The divergence of opinion is natural, since in most discussions of property the opposing theorists have usually been discussing different things. Property is the most ambiguous of categories. It covers a multitude of rights which have nothing in common except that they are exercised by persons and enforced by the State. {54} Apart from these formal characteristics, they vary indefinitely in economic character, in social effect, and in moral justification. They may be conditional like the grant of patent rights, or absolute like the ownership of ground rents, terminable like copyright, or permanent like a freehold, as comprehensive as sovereignty or as restricted as an easement, as intimate and personal as the ownership of clothes and books, or as remote and intangible as shares in a gold mine or rubber plantation. It is idle, therefore, to present a case for or against private property without specifying the particular forms of property to which reference is made, and the journalist who says that "private property is the foundation of civilization" agrees with Proudhon, who said it was theft, in this respect at least that, without further definition, the words of both are meaningless. Arguments which support or demolish certain kinds of property may have no application to others; considerations which are conclusive in one stage of economic organization may be almost irrelevant in the next. The course of wisdom is neither to attack private property in general nor to defend it in general; for things are not similar in quality, merely because they are identical in name. It is to discriminate between the various concrete embodiments of what, in itself, is, after all, little more than an abstraction.