commutation. These consist in the use of certain externals, whether things, persons, or even works: of things as when one man takes from or restores to another that which is his: of persons as when a man does an injury to the very person of another…: and of works as when a man justly enacts a work of another or does a work for him…. Commutative justice directs commutations that can take place between two persons. Of these some are involuntary, some voluntary…. Voluntary commutations are when a man voluntarily transfers his chattel to another person. And if he transfer it simply so that the recipient incurs no debt, as in the case of gifts, it is an act not of justice, but of liberality. A voluntary transfer belongs to justice in so far as it includes the notion of debt.' Aquinas then goes on to distinguish between the different kinds of contract, sale, usufruct, loan, letting and hiring, and deposit, and concludes, 'In all these actions the mean is taken in the same way according to the equality of repayment. Hence all these actions belong to the one species of justice, namely, commutative justice.'[2]

[Footnote 1: ii. ii. 61, 2.]

[Footnote 2: ii. ii. 61, 3. The reasoning of Aristotle is characteristically reinforced by the quotation of Matt. vii. 12; ii. ii. 77,1.]

This is not the place to discuss the precise meaning of the equality upon which Aquinas insists, which will be more properly considered when we come to deal with the just price. What is to be noticed at present is that all the transactions which are properly comprised in a discussion of economic theory—sales, loans, etc.—are grouped together as being subject to the same regulative principle. It therefore appears more correct to approach the subject which we are attempting to treat by following that principle into its various applications, than by making one particular application of the principle the starting-point of the discussion.

It will be noticed, however, that the principles of commutative justice all treat of the commutations of external goods—in other 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 the case of the sale of the use of money. The last matter with which we shall deal is the machinery by which exchanges are conducted, namely, money. Many other subjects, such as slavery and the legitimacy of commerce, will be treated as they arise in the course of our treatment of these principal divisions.

In its ultimate analysis, the whole subject may be reduced to a classification of the various duties which attached to the right of private property. The owner of property, as we shall see, was bound to observe certain duties in respect of its acquisition and its consumption, and certain other duties in respect of its exchange, whether it consisted of goods or of money. The whole fabric of mediæval economics was based on the foundation of private property; and the elaborate and logical system of regulations to ensure justice in economic life would have had no purpose or no use if the subject matter of that justice were abolished.

It must not be understood that the mediæval writers treated economic subjects in this order, or in any order at all. As we have already said, economic matters are simply referred to in connection with ethics, and were not detached and treated as making up a distinct body of teaching. Ashley says: 'The reader will guard himself against supposing that any mediæval writer ever detached these ideas from the body of his teaching, and put them together as a modern text-book writer might do; or that they were ever presented in this particular order, and with the connecting argument definitely stated.'[1]

[Footnote 1: Op. cit., vol. i. pt. ii. p. 387.]