A complete individual nature or substance, when it exists in the actual order, really distinct and separate in its own complete entity from every other existing being, exercising its powers and discharging its functions of its own right and according to the laws of its own being, is said to _subsist_, or to have the perfection of _subsistence_. In this state it not only _exists in itself_ as every substance does; it is not only _incommunicable_ to any other being as every individual is, in contradistinction with _second_ or _universal_ substances which are, as such, indefinitely communicable to individuals; but it is also a complete whole, incommunicable _as a mere integral or essential part_ to some other whole, unlike the incomplete substantial constituents, or integral parts, members or organs of, say, an individual organic body; and finally it is incommunicable in the sense that it is not capable of being assumed into the subsisting unity of some other superior “suppositum” or “person”. All those characteristics we find in the individual “subsisting thing” or “person”. It “exists in itself” and is not communicable to another substance _as an accident_, because it is itself a substance. It is not communicable _to individuals as a universal_, because it is itself an individual. It is not communicable _as an integral or essential part to a whole_, because it is itself a complete substance and nature.(286) Finally it is not communicable to, and cannot be assumed into, the unity of a higher personality so as to subsist by virtue of the latter’s subsistence, because it has a perfection incompatible with such assumption, _viz._ its own proper subsistence, whereby it is already an actually subsisting thing or person in its own right, or _sui juris_, so to speak. The mention of this last sort of incommunicability would be superfluous, and indeed unintelligible, did we not know from Divine Revelation that the human nature of our Divine Lord and Saviour, Jesus Christ, though it is a complete and most perfect individual nature, is nevertheless _not a person_, because It is assumed into the Personality of the Second Person of the Divine Trinity, and, united hypostatically or personally with this Divine Person, subsists by virtue of the Divine Subsistence of the latter.