As to the use of land, we hold: That —
  While the right of ownership that justly attaches to things produced by
    labor cannot attach to land, there may attach to land a right of possession.
    As your Holiness says, “God has not granted the earth to mankind in
    general in the sense that all without distinction can deal with it as they
    please,” and regulations necessary for its best use may be fixed by
    human laws. But such regulations must conform to the moral law — must
    secure to all equal participation in the advantages of God’s general
    bounty. The principle is the same as where a human father leaves property
    equally to a number of children. Some of the things thus left may be incapable
    of common use or of specific division. Such things may properly be assigned
    to some of the children, but only under condition that the equality of benefit
    among them all be preserved.
  In the rudest social state, while industry consists in hunting, fishing,
    and gathering the spontaneous fruits of the earth, private possession of
    land is not necessary. But as men begin to cultivate the ground and expend
    their labor in permanent works, private possession of the land on which labor
    is thus expended is needed to secure the right of property in the products
    of labor. For who would sow if not assured of the exclusive possession needed
    to enable him to reap? who would attach costly works to the soil without
    such exclusive possession of the soil as would enable him to secure the benefit?
  This right of private possession in things created by God is however very
    different from the right of private ownership in things produced by labor.
    The one is limited, the other unlimited, save in cases when the dictate of
    self-preservation terminates all other rights. The purpose of the one, the
    exclusive possession of land, is merely to secure the other, the exclusive
    ownership of the products of labor; and it can never rightfully be carried
    so far as to impair or deny this. While any one may hold exclusive possession
    of land so far as it does not interfere with the equal rights of others,
    he can rightfully hold it no further.
  Thus Cain and Abel, were there only two men on earth, might by agreement
    divide the earth between them. Under this compact each might claim exclusive
    right to his share as against the other. But neither could rightfully continue
    such claim against the next man born. For since no one comes into the world
    without God’s permission, his presence attests his equal right to the
    use of God’s bounty. For them to refuse him any use of the earth which
    they had divided between them would therefore be for them to commit murder.
    And for them to refuse him any use of the earth, unless by laboring for them
    or by giving them part of the products of his labor he bought it of them,
    would be for them to commit theft. ...
  
    God’s laws do not change. Though their applications may alter with
    altering conditions, the same principles of right and wrong that hold when
    men are few and industry is rude also hold amid teeming populations and complex
    industries. In our cities of millions and our states of scores of millions,
    in a civilization where the division of labor has gone so far that large
    numbers are hardly conscious that they are land-users, it still remains true
    that we are all land animals and can live only on land, and that land is
    God’s bounty to all, of which no one can be deprived without being
    murdered, and for which no one can be compelled to pay another without being
    robbed. But even in a state of society where the elaboration of industry
    and the increase of permanent improvements have made the need for private
    possession of land wide-spread, there is no difficulty in conforming individual
    possession with the equal right to land. For as soon as any piece of land
    will yield to the possessor a larger return than is had by similar labor
    on other land a value attaches to it which is shown when it is sold or rented.
    Thus, the value of the land itself, irrespective of the value of any improvements
    in or on it, always indicates the precise value of the benefit to which all
    are entitled in its use, as distinguished from the value which, as producer
    or successor of a producer, belongs to the possessor in individual right.
  To combine the advantages of private possession with the justice of common
    ownership it is only necessary therefore to take for common uses what value
    attaches to land irrespective of any exertion of labor on it. The principle
    is the same as in the case referred to, where a human father leaves equally
    to his children things not susceptible of specific division or common use.
    In that case such things would be sold or rented and the value equally applied.
  It is on this common-sense principle that we, who term ourselves single-tax
    men, would have the community act.
  We do not propose to assert equal rights to land by keeping land common,
    letting any one use any part of it at any time. We do not propose the task,
    impossible in the present state of society, of dividing land in equal shares;
    still less the yet more impossible task of keeping it so divided.
  We propose — leaving land in the private possession of individuals,
    with full liberty on their part to give, sell or bequeath it — simply
    to levy on it for public uses a tax that shall equal the annual value of
    the land itself, irrespective of the use made of it or the improvements on
    it. And since this would provide amply for the need of public revenues, we
    would accompany this tax on land values with the repeal of all taxes now
    levied on the products and processes of industry — which taxes, since
    they take from the earnings of labor, we hold to be infringements of the
    right of property.
  This we propose, not as a cunning device of human ingenuity, but as a conforming
    of human regulations to the will of God.
  God cannot contradict himself nor impose on his creatures laws that clash.
  If it be God’s command to men that they should not steal — that
    is to say, that they should respect the right of property which each one
    has in the fruits of his labor;
  And if he be also the Father of all men, who in his common bounty has intended
    all to have equal opportunities for sharing;
  Then, in any possible stage of civilization, however elaborate, there must
    be some way in which the exclusive right to the products of industry may
    be reconciled with the equal right to land.
  If the Almighty be consistent with himself, it cannot be, as say those socialists
    referred to by you, that in order to secure the equal participation of men
    in the opportunities of life and labor we must ignore the right of private
    property. Nor yet can it be, as you yourself in the Encyclical seem to argue,
    that to secure the right of private property we must ignore the equality
    of right in the opportunities of life and labor. To say the one thing or
    the other is equally to deny the harmony of God’s laws.
  But, the private possession of land, subject to the payment to the community
                of the value of any special advantage thus given to the individual,
    satisfies both laws, securing to all equal participation in the bounty of
    the Creator
                and to each the full ownership of the products of his labor.
    ... read the whole letter