B. About the Extrinsic Medium

87. [The opinion of others] - As to the second principal article [n.56], about the extrinsic medium, the position is taken [Aquinas, Bonaventure] that grace was the medium of congruity in this [hypostatic] union.

88. [Rejection of the opinion] - Against this position I argue first that in the instant of nature in which the nature would be a person in itself if it were not assumed, it would, in the same instant, be a person in another when it is assumed (this was made clear in the first article [n.56]); but it would naturally first be a person in itself before it had the habit of grace, because the habit is the principle of operating and consequently is the perfection of that to which operating belongs; but to operate belongs to a supposit; therefore the nature would first naturally have the idea of supposit in itself before it had any grace or habit, which alone is the principle of operating. Therefore when it is assumed too it is naturally united first before grace is given to it; therefore grace is not the medium.

89. There is also a confirmation, because what belongs in itself to another belongs to it before something else does if that something else belongs to it per accidens; nature, if left to itself, would be a person in itself and of itself; therefore that would belong to nature first before the accidental habit did.

90. Again, John 1.14, “We saw his glory as of the only begotten from the Father” - where John seems to say that ‘to be only begotten’ is the proximate reason for the congruence whereby he [the Lord] has the fullness of grace; therefore the nature was subsistent in the Word before so great a grace was conferred on it, because it would seem improper for so great a fullness of grace to be conferred on the nature in an instant in which the nature is understood not to be united with the Word.

91. Further, the grace would not formally unite [nature with the Word] (as is plain), so grace would be disposed in idea of a disposition in the other extreme; but this is false,a because the nature itself, where grace is, is a person, and for that reason all its accidents are united to the person accidentally and mediately; therefore in the case of this union no accident could have been the medium (just as neither is whiteness the medium in the union of surface with body).

a.a [Interpolation] because the real and actual existence of an accident presupposes, in the order of nature, the real existence of the subject; but grace is in the soul of Christ as an accident in a subject; therefore its real and actual existence presupposes the real existence of the soul. But the soul of Christ only had real existence in the Word; therefore the soul was assumed by the Word first in the order of nature before it was the subject of grace.