The website includes the following:
Letter On The Common Good
Charles de Koninck
December 22, 1961
Dear Sister Margaret Ann:
The book you mention was out of print six weeks after publication. A new printing will appear in France some time next year.
I wrote that little work to defend Aristotle and St. Thomas when they say that, within a given genus, the common good is always more divine than the proper or personal good. This proposition had been under attack for some time. The reasoning behind this open attack even by well-known Thomists assumed that "common good" is a univocal expression, i.e. with one single meaning, and that one can therefore pass from one genus to the other. Yet in fact the common good of the family (namely, the offspring) and that of the political community (the well-being of the citizens, which, in the end, consists in virtuous activity) are one only in proportion. When said of the Church, we must distinguish between the intrinsic common good, which is the inherent good of the whole made up of parts; and the extrinsic common good, which is God in his very Deity. The latter is a common good in still another sense, for it refers to what St. Thomas calls a "totum ante partes", not "ex partibus." When we say that the creature participates in God's perfection, we do not mean that it is part of God the way a slice of bread is part of the whole loaf. It means simply that the fulness of God's perfection is such that, no matter how perfect the creature or even the ensemble of all creation, it will never compare to God except in the way in which what is only partial compares to the whole. Hence, had God created only one single person, he would still have the nature of common good in the latter sense; so that this person would have to love God as a good that far exceeds the measure of any created person. And this is the basis of charity towards neighbour, whom we must love qua "capax Dei". This is so true that one cannot love God without love of neighbour. Had God produced but one person, this person would still have to love God in his super-abundant communicability to others. This applies even to the soul of Christ, which, in the beatific vision does not see God comprehensively.
It is one thing to compare the member of a society to the society as a whole. The society is for the sake of the common good of its members who are individual persons. Hence society is for man, not man for society. But it does not follow from this that the common good of society must be broken down into individual goods, the way a loaf of bread is shared at the table. In the Eucharist, however, which St. Thomas calls the spiritual common good of the whole Church, "Sumit unus, sumunt mille, quantum iste, tantum ille."
You say: "If we are part of the whole living Christ, then I conclude that the part exists for the whole, and not the whole for the part." Concerning the Mystical Body, three kinds of good are involved. If you consider the perfection of this complex whole as such, then each member, the humanity of Christ most of all, contributes to the perfection or good of the whole; and, in this respect, the member is for the whole the way feet and eyes are for the good of the whole body. But the perfection of the whole flows back to the members, though to the members as their common good. Finally, if we consider the ultimate purpose of the Mystical Body, it is the Deity itself, the extrinsic common good, achieved, immediately, by the individual persons severally. The point is that in God's designs we are in fact dependent upon one another; he has chosen teachers, ministers of the Sacramenta, etc. Now, all this bespeaks dependence on the part of those who are taught and partake in the Sacraments. But we cannot day that the ultimate good of the Mystical Body is the good that is intrinsic to it as an orderly whole of parts; this itself is for the sake of something else, namely, the extrinsic good which is God in his Deity.
Let me put it this way, by analogy: The proper good of the eye is to see; but its seeing contributes to the good of the whole man; but the whole man is not for the sake of the eye's seeing; yet, without sight, the whole would be maimed. But here is where the comparison breaks down: eyes are for seeing and for nothing else; but the teacher, whom St. Thomas calls an eye of the Mystical Body, is not, in all that he is, for the sake of teaching. The immediate good of the teacher is to enlighten those whom he teaches; It is good for him to do so, and good for those taught. But teaching is not his ultimate end as a person; his teaching serves this end, which is to know God as he is in Himself; and he wants those whom he teaches to attain this same end, and to attain it in their individual persons.
See also: Charles de Koninck Archive and the Charles De Koninck Scribd group.
Charles De Koninck, the Common Good, and the Human Environment (pdf)