Here the contention is that we can have “the same person” and yet not necessarily “the same identical substance,” because _consciousness_ may give a personal unity to distinct and successive substances in the individual man just as _animal life_ gives an analogous unity to distinct and successive substances in the individual animal. This is very superficial; for it only substitutes for the problem of human personality the similar problem of explaining the unity and sameness of subsistence in the individual living thing: a problem which involves the fact of _memory_ in animals. For scholastic philosophers unity of life in the living thing, involving the fact of memory in animals, is explained by the perfectly intelligible and will-grounded teaching that there is in each individual living thing a _formative and vital principle_ which is _substantial_, a _forma substantialis_, which unites, in the _abiding self-identical unity of a complete individual composite substance_, the material principle of the corporeal substances which thus go, in the incessant process of substantial change known as metabolism, to form partially, and to support the substantial continuity of, the living individual. While the latter is thus in constant process of material, or partial, substantial change, it remains, as long as it lives, the same complete individual substance, and this in virtue of the abiding _substantial_ formative and vital principle which actuates and animates it. The abiding permanence or self-identity of the _subsisting individual substance_ which feels or thinks, and remembers, is an intelligible, and indeed the only intelligible, ground and explanation of memory, and of our consciousness of personal identity.