Substitution

Substitution (substitutio) was the appointment of another heir (heres substitutus) by the testator in the place of an instituted heir in the event that the latter could not or did not wish to inherit.

The substitutio vulgaris was the usual and least complicated form of substitution which occurred when the testator wished to avoid dying intestate. He simply appointed a second heir as a substitute for the original heir. In this way the testator could appoint a whole succession of substitute heirs in his will with, in the final instance, one of his slaves as a heres necessarius.^[1091] This form of substitution may be described as an institution of an heir subject to a suspensive condition; namely, that the original heir for some reason failed to inherit.^[1092]

The substitutio pupillaris related to the inability of a person below the age of puberty (impubes) to compose a will. If a paterfamilias thought that his child whom he had instituted as heir might die before reaching the age of puberty, he could by virtue of his potestas nominate the person who should succeed in that case. This form of substitution had two aspects: in the first place the testator stipulated that if the child did not for some reason inherit, a third person would inherit in his place; he then supplemented this stipulation by adding that if the child should inherit but die before reaching the age of puberty (i.e., before becoming capable of creating a will), another person would assume his place.^[1093] The first part of this substitution was no different from the substitutio vulgaris, while the second part was termed substitutio pupillaris. One might surmise that such a case featured in effect two wills: one of the father himself and one the father composed on the strength of his potestas for the impubes, who himself could not craft a will.

The third form of substitution, known as substitutio quasi-pupillaris or substitutio exemplaris, was introduced by Justinian in respect of persons with mental defects. Following the model of the substitutio pupillaris, Justinian empowered a testator to appoint substitutes for his children of further descendants who were insane or otherwise mentally deficient. The right to effect a substitution of this kind could be exercised not only by the paterfamilias but also any ascendant, such as a mother who instituted a mentally deficient person as heir. However, the choice of substitutes was limited to descendants or, should there be no such person, brothers and sisters of the insane person. Once again, the underlying idea was that an insane person could not himself compose a valid will and, therefore, this task was performed by an ascendant on his behalf.^[1094]

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