[POMPONIUS libro sexto ad Sabinum. ] §36.2.13.prHuiusmodi legatum: 'siue illud factum fuerit siue non fuerit, illi do lego', ad heredem non transit, nisi alter casus uiuo legatario exstiterit, quoniam causa, ex qua debeatur, praecedere semper debet.
[POMPONIUS in the sixth book on Sabinus.] A legacy of this kind: 'whether that be done or not be done, I give and bequeath to him', does not pass to the heir, unless one of the two events has occurred during the lifetime of the legatee, since the ground from which it becomes due must always precede.
nec, quia certum est alterutrum futurum, omnimodo debebitur: nam tale legatum, 'cum morietur, heres dato', certum est debitum iri et tamen ad heredem legatarii non transit, si uiuo herede decedat.
Nor, because it is certain that one or the other will happen, will it be due unconditionally: for such a legacy as 'when my heir dies, let my heir give it' is certain to become due, and yet it does not pass to the heir of the legatee if the legatee dies while the heir is still alive.