[IDEM libro secundo manualium. ] §41.3.48.prSi existimans debere tibi tradam, ita demum usucapio sequitur, si et tu putes debitum esse.
[THE SAME, On Manuals, book 2] If, believing that I owe you something, I deliver it to you, usucapion follows only if you also believe that it is owed.
aliud, si putem me ex causa uenditi teneri et ideo tradam: hic enim nisi emptio praecedat, pro emptore usucapio locum non habet.
It is different if I believe that I am bound by a contract of sale and therefore deliver it; for in this case, unless a sale has preceded, usucapion "as purchaser" does not take place.
diuersitatis causa in illo est, quod in ceteris causis solutionis tempus inspicitur neque interest, cum stipulor, sciam alienum esse nec ne: sufficit enim me putare tuum esse, cum soluis: in emptione autem et contractus tempus inspicitur et quo soluitur: nec potest pro emptore usucapere, qui non emit, nec pro soluto, sicut in ceteris contractibus.
The reason for this difference is that in other cases of acquisition, the time of performance is looked at, and it does not matter whether I know or not that the thing belongs to another when I stipulate; for it is sufficient that I believe it to be yours when you perform. In sale, however, both the time of the contract and the time at which performance is made are looked at; and he who did not buy cannot acquire by usucapion "as purchaser," nor can he do so "as on performance," as in other contracts.