[IDEM libro octauo quaestionum. ] §12.6.56.prSufficit ad causam indebiti incertum esse, temporaria sit an perpetua exceptionis defensio.
[THE SAME, in the eighth book of Questions.] It is sufficient for the ground of an undue payment that it is uncertain whether the defense of an exception is temporary or perpetual.
nam si qui, ne conueniatur, donec Titius consul fiat, paciscatur, quia potest Titio decedente perpetua fieri exceptio, quae ad tempus est Titio consulatum ineunte, summa ratione dicetur, quod interim soluitur, repeti: ut enim pactum, quod in tempus certum collatum est, non magis inducit condictionem, quam si ex die debitor soluit, ita prorsum defensio iuris, quae causam incertam habet, condictionis instar optinet.
For if anyone should agree that he is not to be sued until Titius becomes consul, because the exception—which is temporary if Titius enters upon the consulship—can become perpetual if Titius dies, it will be said with the greatest reason that what is paid in the meantime can be recovered. For just as an agreement which is referred to a fixed time does not induce a recovery any more than if a debtor pays before the day, so indeed a legal defense which has an uncertain cause obtains the force of a recovery.