Short answer. When a will leaves you a choice between two things but does not say who decides, the right to choose belongs to the heir who is obliged to give the legacy. If no particular heir bears that obligation, the executor or administrator of the estate makes the selection instead.
What the law says
the choice is presumed to be left to the heir upon whom the obligation to give the legacy or devise may be imposed, or the executor or administrator of the estate if no particular heir is so obliged
Civil Code, Article 940 — Alternative Legacies. Read the full provision →
Who holds the right to choose
Article 940 of the Civil Code sets the default rule clearly: the choice is presumed to belong to the heir who bears the obligation to deliver the legacy or devise. That heir picks which of the two items you receive. If the will does not saddle any particular heir with that duty — for instance, the estate itself owes the legacy — then the executor or administrator of the estate steps in and makes the selection. The person who must eventually hand over the thing is the one who gets to decide which thing it will be.
What happens if that heir or legatee dies before choosing
The right to choose does not lapse simply because the person who held it dies before exercising it. Under the same article, the right passes to the respective heirs of that person. So if the heir who was supposed to pick dies intestate or under a separate will, their own heirs inherit the decision-making power. This matters in practice: if you are the legatee waiting for someone else to choose, a death in the obligated heir's family does not automatically entitle you to pick for yourself — it moves the choice to a new set of people, not to you.
Once the choice is made, it cannot be taken back
Article 940 is explicit: once made, the choice is irrevocable. The moment the selecting party communicates their decision — whether to you or to the estate — that selection is locked in. There is no changing it later on the grounds of regret or a better deal. This protects you as the legatee: once the choosing party has committed, they cannot switch to the other item. If you are the one waiting to receive the legacy, it is worth confirming that a clear communication of the choice has actually been made before treating the matter as settled.
The general rules on alternative obligations still apply
Article 940 also points out that, except for what it specifically addresses, the provisions of the Civil Code regulating obligations of the same kind shall be observed — meaning the broader framework for alternative obligations governs questions the succession article does not directly answer. If one of the two items is lost or destroyed before the choice is made, for example, the surviving item becomes what the legatee receives. These background rules fill in the gaps the will left open, and they operate alongside the succession-specific rules in Article 940.