10 So strong and convincing are these arguments that it seems amazing that some should now be setting up anew certain obsolete opinions in opposition to what is here laid down. They assert that it is right for private persons to have the use of the soil and its various fruits, but that it is unjust for any one to possess outright either the land on which he has built or the estate which he has brought under cultivation. But those who deny these rights do not perceive that they are defrauding man of what his own labor has produced. For the soil which is tilled and cultivated with toil and skill utterly changes its condition; it was wild before, now it is fruitful; was barren, but now brings forth in abundance. That which has thus altered and improved the land becomes so truly part of itself as to be in great measure indistinguishable and inseparable from it. Is it just that the fruit of a man's own sweat and labor should be possessed and enjoyed by any one else? As effects follow their cause, so is it just and right that the results of labor should belong to those who have bestowed their labor.
Source: Rerum Novarum (Vatican.va)