A lot of people have made use of a picture of Inigo Montoya from Princess Bride and the quotation, "You Keep Using That Word, I Do Not Think It Means What You Think It Means," with reference to some disputed term or other. I think it would be humorous to make one of these photos with "common good."
Is the definition of the common good (along with subsidiarity), as put forth by contemporary CST and used by Mr. Olson, helpful? Yes, but primarily with reference to the modern nation-state. He cites the Compendium: "The common good of society is not an end in itself; it has value only in reference to attaining the ultimate ends of the person and the universal common good of the whole of creation. " The political common good, as "traditionally" understood by Thomists and Aristotelians, is not the same as the instrumental good defined by John XXIII and adopted into contemporary CST. The common good, the good of the community, is an end in itself - desirable for its own sake and not merely as a means to an end desired for itself. This does not mean that it is not subordinate to a "higher" end or good, like the supernatural common good (and man's ultimate end), God Himself. The common good, as defined within contemporary CST, may be an instrumental good to the political common good, but it is not identical to the political common good:
The principle of the common good, to which every aspect of social life must be related if it is to attain its fullest meaning, stems from the dignity, unity and equality of all people. According to its primary and broadly accepted sense, the common good indicates “the sum total of social conditions which allow people, either as groups or as individuals, to reach their fulfilment more fully and more easily”.This instrumental good is explained as such by proponents of the New Natural Law Theory, for example. And yet there is use of language usually associated with the traditional [definition of the] common good:
The common good does not consist in the simple sum of the particular goods of each subject of a social entity. Belonging to everyone and to each person, it is and remains “common”, because it is indivisible and because only together is it possible to attain it, increase it and safeguard its effectiveness, with regard also to the future. Just as the moral actions of an individual are accomplished in doing what is good, so too the actions of a society attain their full stature when they bring about the common good. The common good, in fact, can be understood as the social and community dimension of the moral good.An explanation of how the common good is common, though it may have been better to explain how it is common or shared - not as belonging to them, like property (in which case common would be said in praedicando), but as a shared end. And in the next paragraph:
A society that wishes and intends to remain at the service of the human being at every level is a society that has the common good — the good of all people and of the whole person  — as its primary goal. The human person cannot find fulfilment in himself, that is, apart from the fact that he exists “with” others and “for” others. This truth does not simply require that he live with others at various levels of social life, but that he seek unceasingly — in actual practice and not merely at the level of ideas — the good, that is, the meaning and truth, found in existing forms of social life. No expression of social life — from the family to intermediate social groups, associations, enterprises of an economic nature, cities, regions, States, up to the community of peoples and nations — can escape the issue of its own common good, in that this is a constitutive element of its significance and the authentic reason for its very existence
Can the second part of this section be harmonized with the first? If the common good is the "social and community [communal] dimension of the moral good [the life of virtue]" then is it the same as "the sum total of social conditions which allow people, either as groups or as individuals, to reach their fulfilment more fully and more easily"?
As for Fr. Barron's essay -- "Now in Catholic social theory, subsidiarity is balanced by solidarity, which is to say, a keen sense of the common good, of the natural and supernatural connections that bind us to one another, of our responsibility for each other." Solidarity may be identified with the virtue of social justice (or legal justice), or with civic friendship, or both, depending on, of course, its definition. The Compendium:
Solidarity is also an authentic moral virtue, not a “feeling of vague compassion or shallow distress at the misfortunes of so many people, both near and far. On the contrary, it is a firm and persevering determination to commit oneself to the common good. That is to say to the good of all and of each individual, because we are all really responsible for all”. Solidarity rises to the rank of fundamental social virtue since it places itself in the sphere of justice. It is a virtue directed par excellence to the common good, and is found in “a commitment to the good of one's neighbour with the readiness, in the Gospel sense, to ‘lose oneself' for the sake of the other instead of exploiting him, and to ‘serve him' instead of oppressing him for one's own advantage (cf. Mt 10:40-42, 20:25; Mk 10:42-45; Lk 22:25-27)”.I've already written about subsidiarity (as well as the contemporary notion of common good) and how these terms probably are better understood as reactions to the growth of the modern nation-state and polities that are too big for their own good, and the concomitant political and economic centralization. This may have been a conscious formulation for the first theorists, but those currently presenting CST as a basis for seeking political solutions may be unaware of the original contextual background of the terms.
Is the whole greater than the sum of its parts when we consider the [political] community and its members? Is legal justice distinct from civic friendship? I will have to address these questions at some other time. At some point I will also have to rewrite the discussion of how one cannot talk about common good if a community is mostly absent and the potential for community must be developed first, addressing the need for a common culture and a single identity, one people. Taking the United States as one nation, or polity, is a problem, because the scale is too big and the relationship between all of its members to one another too tenuous for the most part. Talking about the common good (and subsidiarity and solidarity) when the current political order (taken broadly as to referring not only to the federal government but also the culture and social order), or constitution in the Aristotelian sense, mitigates against it.