Short answer. It is a substitution where the first heir, called the fiduciary, is entrusted with preserving and later transmitting the inheritance to a second heir. Article 863 makes it valid only if the substitution goes no further than one degree from the heir originally instituted, and both the fiduciary and the second heir are alive when the testator dies.
What the law says
A fideicommissary substitution by virtue of which the fiduciary or first heir instituted is entrusted with the obligation to preserve and to transmit to a second heir the whole or part of the inheritance, shall be valid and shall take effect, provided such substitution does not go beyond one degree from the heir originally instituted, and provided further, that the fiduciary or first heir and the second heir are living at the time of the death of the testator.
Civil Code, Article 863 — Fideicommissary Substitution. Read the full provision →
Two heirs, one obligation between them
Article 863 describes a fideicommissary substitution as one by virtue of which the fiduciary or first heir instituted is entrusted with the obligation to preserve and to transmit to a second heir the whole or part of the inheritance. The first heir, called the fiduciary, does not simply receive the inheritance outright and freely. He holds it under an obligation — to preserve it, and in time to transmit it to the second heir the testator named to receive it afterward.
The one-degree limit
The article does not leave this arrangement open-ended. It is valid only provided such substitution does not go beyond one degree from the heir originally instituted. That limit prevents a testator from chaining together an indefinite sequence of successive heirs, each holding for the next. The obligation to preserve and transmit can run from the first heir to a second — one degree — but the statute stops the substitution there.
Both heirs must be alive when the testator dies
Article 863 adds a second condition for validity: the fiduciary or first heir and the second heir are living at the time of the death of the testator. Both people in the arrangement — the one entrusted with preserving the inheritance and the one who is eventually to receive it — need to exist and be alive at that moment. If either condition in the article is not met, the substitution as described does not take effect.
What this means for the property involved
Because the fiduciary's role is defined as one of preservation rather than free disposal, the whole point of Article 863 is that the property — the whole or part of the inheritance — is meant to reach the second heir substantially intact. The fiduciary is not simply an heir who happens to be asked to pass something along later; the obligation to preserve is built into the substitution itself, for as long as the arrangement Article 863 describes remains in effect.