GAI INSTITUTIONVM
LIBER III§88. (Nunc transeamus) ad obligationes, quarum summa diuisio in duas species diducitur: omnis enim obligatio uel ex contractu nascitur uel ex delicto.
§89. Et prius uideamus de his quae ex contractu nascuntur. harum autem quattuor genera sunt: aut enim re contrahitur obligatio aut uerbis aut litteris aut consensu.
§90. Re contrahitur obligatio uelut mutui datione: [mutui autem datio] proprie in his [fere] rebus contingit quae pondere numero mensura constant, qualis est pecunia numerata uinum oleum, frumentum aes argentum aurum; quas res aut numerando aut metiendo aut pendendo in hoc damus, ut accipientium fiant et quandoque nobis non eaedem sed aliae eiusdem naturae reddantur: unde etiam mutuum appellatum est, quia quod ita tibi a me datum est ex meo tuum fit.
§91. Is quoque qui non debitum. accepit ab eo qui per errorem soluit re obligatur; nam proinde ei condici potest SI PARET EVM DARE OPORTERE, ac si mutuum accepisset. unde quidam putant pupillum aut mulierem, cui sine tutoris auctoritate non debitum per errorem datum est, non teneri condictione non magis quam mutui datione. sed haec species obligationis non uidetur ex contractu consistere, quia is qui soluendi animo dat magis distrahere uult negotium quam contrahere.
(Ed. by J. Muirhead. The Institutes of Gaius and the Rules of Ulpian. Edinburgh: Clark, 1904)
§ 88. Let us now pass to obligations, of which the chief division is into two species; for every obligation arises either from contract or from tort.
§ 89. And, first, let us look into those which arise from contract. Of these, there are four kinds; for an obligation is contracted either by the thing, or by words, or by writing, or by consent.
§ 90. An obligation is contracted by means of the thing itself, as in the case of a loan in kind. The contract of loan in kind properly applies to those things which are estimated by weight, number, or measure, such as coined money, wine, oil, corn, copper, silver, gold, which things we give either by counting, or measuring, or weighing them, in order that they may become the property of those receiving them, and the identical things are not returned to us, but others of the same nature; and, hence, this is called a "mutuum", because that which has been so given by me to you from being mine becomes yours.
§ 91. He, also, who receives a thing which is not owed to him from a person who pays it by mistake, is bound by the thing, for he can be sued by the personal action, "if it appear that he ought to give", just as if he had received a loan in kind. Hence, some think that a pupil, or a woman to whom, without the authorisation of the tutor, something has been paid by mistake which was not due, is not liable to a personal action, any more thin by the giving of a loan in kind. But this kind of obligation does not seem to arise out of contract, since be who gives with the intention of paying, is rather desirous of dissolving than of forming an obligation.
Trans. by J. Muirhead. The Institutes of Gaius and the Rules of Ulpian. Edinburgh: Clark, 1904)
