If the rejoinder be made that Pope Leo could have had no other group of persons in mind than the Single Taxers, when he wrote the paragraph quoted above, our answer must be that he did not definitely identify them, either by naming them, as he named the Socialists, or by any other sufficiently explicit designation. Applying to this paragraph the customary and recognised rules of interpretation, we are obliged to conclude that it does not contain an explicit condemnation of the Single Tax system. To put the substance of this chapter in two sentences: Private landownership is a natural right because in present conditions the institution is necessary for individual and social welfare. The right is certainly valid as against complete Socialism, and probably valid as against any such radical modification of the present system as that contemplated by the thoroughgoing Single Taxers. FOOTNOTES: [34] The marriage rights of criminals, degenerates, and other socially dangerous persons, are passed over here as not pertinent to the present discussion. For the same reason nothing is said of the perfectly valid _social_ argument in favour of the individual right of marriage. [35] Cf. Vermeersch, "Quaestiones de Justitia," no. 204. [36] The argument in the text is obviously empirical, drawn from consequences. There is, however, a putatively intrinsic or metaphysical argument which is sometimes urged against the justice of the Single Tax system. It runs thus: since the fruits of a thing belong to the owner of the thing, "res fructificat domino," rent, which is the economically imputed fruit of land, necessarily and as a matter of natural right should go to the owner of the land. As will be shown later, the formula at the basis of this contention is not a metaphysical principle at all, but a conclusion from experience. Like every other formula or principle of property rights, it must find its ultimate basis in human welfare. [37] Liberatore, "Principles of Political Economy," pp. 130, 134. [38] Cf. Vermeersch, op. cit., no. 210; Ryan, "Alleged Socialism of the Church Fathers." [39] "In IV Sent.," d. 15, q. 2, n. 5; and "Reportata parisiensia," d. 15, q. 4, n. 7-12. [40] "De Justitia et Jure," tr. 2, d. 18 and 20. [41] "De Justitia et Jure," c. 5, n. 3. [42] "De Legibus," l. 2, c. 14, n. 13 and 16. [43] "In Summa," 1ma 2ae, d. 157, n. 17. [44] "De Justitia et Jure," d. 4, a. 1. [45] "Summa Theologica," 2a 2ae, q. 57, a. 2 and 3. [46] "De Justitia et Jure," d. 6, s. 1, n. 6. CHAPTER VI LIMITATIONS ON THE LANDOWNER'S RIGHT TO RENT