A robust understanding of the relationship between labor and property can be developed from the concepts of order and authority. In this way, we can avoid the nebulous attribution of "value".
A man, by his labor, incorporates something into an order: i.e. it is reordered to some good that is extrinsic to it; the laborer's work is given a new or deepened participation in the order of man, as it were.
The man, whose reason and will has moved it into a more noble participation, assumes authority over it. In a sense, the laborer is a lawgiver over his work. We should here avoid such misattributions as "legitimacy" or "sovereignty". The laborer has authority over his work insofar as it does not contradict with the order in which he himself is a part.
With such an approach to labor, we can honor P. Leo XIII's judgment on the relation of labor and property; viz. that man has the right to property by virtue of reason through labor.
We may also maintain St. Thomas' position; viz. that common property is by natural law granted to man to furnish the necessities of life, and private property is a matter of positive law. Positive law builds, as it were, on the natural law; human authority maintains the order of society (a perfectly natural thing) by promulgating among his subjects ordinances of reason for their common good. Labor begins as an ordinance of reason, and is carried out as obedience to that ordinance.
It is not appropriate to consider labor separately from that for which labor is accomplished; labor is immediately undertaken for the sake of the social order of the family, and ultimately for the good of the state. Here, too, various extremes may be avoided: The order of the state ought not to be contradicted by so-called "private" interests, yet without the household dimension, (most) labor becomes inordinate by reason of proportion to its end.
Because labor is bound up with order, and property is that over which one has authority by virtue of his labor, not all activities which serve to accumulate possessions are labor, properly speaking; and not all possessions are property. For example, theft, extortion, and usury are intrinsically disordered activities: possessions obtained unjustly are not proper to those who hold them, as opposed to the things a man might get through, say, farming poorly (a disordered, but intrinsically good activity).
