[IDEM libro septuagensimo quarto ad edictum. ] §17.1.46.prSi quis pro eo spoponderit, qui ita promisit: 'si Stichum non dederis, centum milia dabis'? et Stichum redemerit uilius et soluerit, ne centum milium stipulatio committatur, constat posse eum mandati agere.
[THE SAME, On the Edict, Book LXXIV.]\n\nIf anyone has become a guarantor for a person who promised: "If you do not deliver Stichus, will you give one hundred thousand?", and in order that the stipulation for the one hundred thousand should not be forfeited, has purchased Stichus for less and delivered him, it is established that he can bring an action of mandate.
igitur commodissime illa forma in mandatis seruanda est, ut, quotiens certum mandatum sit, recedi a forma non debeat: at quotiens incertum uel plurium causarum, tunc, licet aliis praestationibus exsoluta sit causa mandati quam quae ipso mandato inerant, si tamen hoc mandatori expedierit, mandati erit actio.
Therefore, the most convenient rule to be observed in mandates is that as often as the mandate is certain, one must not depart from its form; but as often as it is uncertain or concerns several matters, then, although the cause of the mandate has been discharged by performances other than those which were inherent in the mandate itself, yet if this was advantageous to the mandator, the action of mandate will lie.