Ad Quintum Mucium libri
Ex libro XXVII
Dig. 12,6,52Idem libro vicensimo septimo ad Quintum Mucium. Damus aut ob causam aut ob rem: ob causam praeteritam, veluti cum ideo do, quod aliquid a te consecutus sum vel quia aliquid a te factum est, ut, etiamsi falsa causa sit, repetitio eius pecuniae non sit: ob rem vero datur, ut aliquid sequatur, quo non sequente repetitio competit.
Ad Dig. 12,6,52Windscheid: Lehrbuch des Pandektenrechts, 7. Aufl. 1891, Bd. II, § 423, Note 11.The Same, On Quintus Mucius, Book XXVII. We make payment either for a good reason or for a purpose, and the reason may depend upon what has already passed, for example, where I make payment because I have obtained something from you or something has been done by you, so that, even if the reason is nonexistent, no action will lie for the recovery of the money; but payment for a purpose is made where some act is to be performed, and if this does not take place, a suit for the recovery of the money will lie.