Hence is it that in man the possession of subsistence belongs neither to the soul nor to the body, and there is no other subsistence in him but the sum of the two natures of which he is composed, but the whole of the two extremes united together, and which is at the same time spirit and body, incorruptible and corruptible, the intelligent and the brute.
Hence, neither the soul nor the body are denominated separately by their respective functions; but it is the whole man who receives the attribution and the different appellations of the actions and states of either nature, and we say, man thinks, man walks, man wills, man grows. Consequently that axiom, Actiones et denominationes sunt suppositorum, Actions are to be attributed to the subsistence. We remark, in the second place, that in the infinite alone the subsistence and personality is necessary, and consequently can never be separated from him or be dependent on any other. Because in this order personality affects a nature essentially complete, total, and of its own intrinsic nature absolutely independent in its action and in its eternal and immutable state, of all external substance.
It follows, therefore, that if a divine personality enters into a finite nature, it must necessarily preserve its own subsistence, since it is evident that, if a divine person is united to a created nature in a manner so close and intimate as to form one single individuality, the created nature, in force of the principles above stated, would have no individuality of its own, and the divine personality would, in such case, necessarily be the supreme and independent principle constituting the new individual, the infinite term and completion of the two natures. Now, such is the hypostatic union. The infinite person of the Word united to himself human nature in a manner so close and intimate as to form one single individuality, Christ Jesus, the Theanthropos; so that the human nature of Christ had no subsistence of its own, but subsisted of the personality of the Word. Hence, in Christ the Word of God was the only supreme and independent principle, who knew himself to be a whole apart, composed of the human and divine natures, who bore alone the attribution and solidarity of the actions springing from either nature, and who was, consequently, the only person in Christ.
But to make the nature of the hypostatic union more intelligible to the reader, we shall dwell upon it a little longer.
We may reduce all the unions between the infinite and the finite to three. The first is the action of God creating finite substances, maintaining them in existence and directing all their movements, permitting, however, their defects and shortcomings.
This is the first and fundamental union between the infinite and the finite. It begins the moment the finite is created, and continues in existence by preservation and concurrence. All this in the natural order. In the supernatural order there is also a first and fundamental union, as we shall see, by which the action of God effects, as it were, a new and superior term, preserves and directs it in its development. Thus, the first union between the finite and the infinite is the action of God effecting a finite term, maintaining it in existence and directing it in its development, both in the substantial and in the sublimative moments. However, this union not only leaves whole and entire the individuality and subsistence of the two terms united, but is not even so close and intimate as to prevent the finite term of the union from occasionally failing in its action, and of falling short of the aim to which it naturally tends. Hence a second and more excellent species of union. By it the infinite is so closely united with the finite as not only to preserve it, and to direct it in all its actions, but also to prevent it from falling into defects and errors.
This second kind of union, though, as it is evident, far exceeding the former in intimacy and perfection, since it implies an extraordinary employment of activity on the part of the infinite, and a special elevation of the finite, is yet not so close as to deprive the finite term of its own subsistence and individuality.[32] We may, therefore, conceive a third kind of union, whereby an infinite personality may be united to a finite nature so closely and so intimately as not only to move and direct it in all its actions, as not only to prevent it from falling into failings and imperfections, but as to make it the intrinsic instrument, the intimate organ of his own infinite action in such a manner as to form of the finite nature and of the infinite personality a new and single individuality.
This supposition is eminently possible. For, on the one hand, the infinite personality being possessed of infinite energy, and, on the other, the finite nature being endowed with an indefinite capacity of sublimation, nothing can detain the first from communicating itself to the second with such energy, power, and intensity of communication as to render it its own most intimate and dependent organ of action. In fact, let the communication of an infinite person to a finite nature be carried to its highest possible degree of union short of absorbing and destroying the real existence of the finite, its substantiality, so to speak; let this finite nature be, accordingly, raised to the highest possible intimacy with the infinite person; let the latter take such intense possession of the former as to make it its own intrinsic organ, the immediate and sole instrument of his own infinite operation, and what will the result be? Why, that the finite nature will no longer possess itself, no longer form a whole by itself separated from and independent of any other; no longer bear the attribution of the actions springing from its nature; in short, it will no longer be a subsistence and an individuality by itself, but will form one single individuality with the divine person, or rather the infinite person will be the only single subsistence of the two natures united, the infinite and the finite. The finite nature in this supposition would stand, with regard to the infinite person, in the same relation in which our body stands with regard to our soul. For the union of body and soul, which constitutes the individual called man, takes place according to this kind of union. The soul is united to the body in a manner so close and so intimate as to render the body its own most intrinsic, dependent instrument, the organ of its operations in such a manner that, in force of this operation, the body does not possess itself, does not form a whole apart, nor is it accountable for the actions which immediately flow from its nature. In other words, it has no subsistence of its own, but subsists of the subsistence of the soul and the whole individual man. The result of this union is possessed of the subsistence and forms one person.
The Incarnation of the Word is like to this union, hence called hypostatic or personal union. The second person of the Trinity united himself to the entire human nature, constituted of body and soul, in a manner so close and intimate as to be himself the subsistence of the human nature; the latter never enjoying a subsistence of its own, because, contemporaneously to the very first instant of its existence, it became the internal, the immediate, and the most intimate organ of the Word of God, and subsisted of the subsistence of the Word, so that it never bore the attribution and solidarity of those actions which have an immediate origin in human nature, but the attribution and solidarity, and, consequently, the moral worth, of those actions belonged to the personality of the Word, according to the axiom that Actiones sunt suppositorum.
Hence the union between the Word of God and his human nature was not a moral union, which always implies the distinct individuality and personality of the two terms united, as Nestorius thought, and many would-be Christians of the present day seem to hold.