1I give that you give, as I give you a Digest that you give me a Code, so that if  I deliver a Digest, you are bound to deliver me a Code. Or if I say, I give that  you do, that is, I give you a Code that you cause a Digest to be written for me. Or  I do that you give, that is, I build you a house that you give me a Code. Or I do  that you do, that is, I build you a hall that you build me a chamber. These gifts  subsist under a modus and bind the contracting parties, so that if I give or do, you  are bound to give or do as you agreed. But they do not enable me to recall what I  have given if you are unwilling to do what you promised. 2I can only sue [to compel  you] to do,3 unless it is otherwise agreed at the beginning. For to this gift subject to  a modus a condition may be added at the outset, as if I say, And if you do not give  or do what you agreed that I may recall what I gave, or recover the charges  incurred in connexion with what4 I did. If no condition is added, however, I  cannot.5
If a gift is made subject to a condition.
 A gift may be made subject to a condition without6 a modus, as where I say, I  give you that thing if something be done or not done, if the condition relates to  the future, 7for though [they may be uncertain to us] the present and past are not  in suspense as the future is; the condition either invalidates the obligation at once  or defers it in no way.8 Then either9 the condition is possible or impossible.10 If  possible and within the donee's power,11 as where I say, I give you such a thing  if you give me ten, the gift is good but suspended until the condition occurs,12  so that if you claim the thing I can except that you have not given me ten. 13If  the condition is impossible, as I give you that thing if you touch the sky with your  finger, the gift is not valid, [but if I say if you do not touch the sky, it is valid],  as though no condition had been imposed.14 A gift is not valid ab initio but in  suspense if the condition is placed in the power of another, as I give you this  thing if Titius wishes me to, or if he so decides, or does such an act, for unless  he does so the gift will not be good. So if the condition is fortuitous, as I give  you such a thing if a ship arrives from Asia, or if Titius is made consul; the gift  will be in suspense because such gifts hang upon the vagaries of fortune.15 If the  condition is mixed, as where it is partly within the donee's power and partly  fortuitous,16 and disjunctive, as I give you this thing if you give me ten [or a ship  arrives from Asia], it suffices if one of the conditions is fulfilled. 17But if several  conditions are annexed conjunctively, as if this and that be done, they all must  be satisfied; if disjunctively, (as said above) it is sufficient to comply with one or  the other of them.1819Some conditions are express and in negative words, as if  Titius is not heir be you heir,20 or if