words, they assume the existence of property of external goods in
individuals. Commutations are but a result of private property; in a
state of communism there could be no commutation. This is well pointed
out by Gerson[1] and by Nider.[2] It consequently is important,
before discussing exchange of ownership, to discuss the principle of
ownership itself; or, in other words, to study the static before the
dynamic state.[3]

[Footnote 1: _De Contractibus_, i. 4 'Inventa est autem commutatio
civilis post peccatum quoniam status innocentias habuit omnia
communia.']

[Footnote 2: _De Contractibus_, v. 1: 'Nunc videndum est breviter unde
originaliter proveniat quod rerum dominia sunt distincta, sic quod
hoc dicatur meum et illud tuum; quia illud est fundamentum omnis
injustitiae in contractando rem alienam, et post omnis injustitia
reddendo eam.']

[Footnote 3: See l'Abbé Desbuquois, _op. cit._, p. 168.]

We shall therefore deal in the first place with the right of private
property, which we shall show to have been fully recognised by the
mediæval writers. We shall then point out the duties which this
right entailed, and shall establish the position that the scholastic
teaching was directed equally against modern socialistic principles
and modern unregulated individualism. The next point with which we
shall deal is the exchange of property between individuals, which is a
necessary corollary of the right of property. We shall show that such
exchanges were regulated by well-defined principles of commutative
justice, which applied equally in the case of the sale of goods and in