ning water, men will
insist upon inquiring why it is not true of land, of articles of food,
of tools and implements, of capital and even, it may be, of the
luxuries upon which a truly human life depends. Accordingly, how to
give a rational account of the so-called natural right of property and
how to fix the natural limits of that right became vexed questions of
philosophical jurisprudence.

Antiquity was content to maintain the economic and social _status quo_
or at least to idealize it and maintain it in an ideal form. The
Middle Ages were content to accept _suum cuique tribuere_ as
conclusive. It was enough that acquisition of land and movables and
private ownership of them were part of the existing social system.
Upon the downfall of authority, seventeenth-and eighteenth-century
jurists sought to put natural reason behind private property as
behind all other institutions. When Kant had undermined this
foundation, the nineteenth-century philosophical jurists sought to
deduce property from a fundamental metaphysical datum; the historical
jurists sought to record the unfolding of the idea of private property
in human experience, thus showing the universal idea; the utilitarian
demonstrated private property by his fundamental test and the
positivist established its validity and necessity by observation of
human institutions and their evolution. In other words, here as
elsewhere, when eighteenth-century natural law broke down, jurists
sought to put new foundations under the old structure of natural
rights, just as natural rights had been put as a new foundation to
support institutions which theretofore had found a sufficient basis in
authority.

Theories by which men have sought to give a rational account of
private property as a social and legal institution may be arranged
conveniently in six principal groups, each including many forms. These
groups may be called: (1) Natural-law theories, (2) metaphysical
theories, (3) historical theories, (4) positive theories, (5)
psychological theories and (6) sociological theories.

Of the natural-law theories, some proceed on a conception of
principles of natural reason derived from the nature of things, some
on conceptions of human nature. The former continue the ideas of the
Roman lawyers. They start with a definite principle found as the
explanation of a concrete case and make it a universal foundation for
a general law of property. As it has been put, they find a postulate