Rerum Novarum launched the movement called Catholic social thought. Successive popes and other Christian thinkers picked up on Leo's themes, defining the common good as "the sum total of social conditions which allow people, either as groups or as individuals, to reach their fulfillment more fully and more easily." Two ideas are particularly significant in this definition. The common good is measured by fulfillment or flourishing—by human beings becoming all they are meant to be. And the common good is about persons, both groups and individuals—not just about "humanity" but about humans, and not just about individuals but about persons in relationship with one another in small groups.
While Rerum Novarum did not prevent the rise of communism in Eastern Europe, it did help Christians resist its totalizing worldview even through decades of repression. One of those Christians, a Polish priest named Karol Wojtyła, occupied Leo's chair and played a pivotal role in the demise of the system whose baleful consequences Leo had foreseen.
Small is Good
The common good can help us avoid two modern temptations—one on the left and one on the right. "Leftists tend to be concerned about 'humanity' as a collective," Notre Dame sociologist Christian Smith told me via e-mail. "If some heads have to roll to improve humanity's lot, so be it. A commitment to the common good opposes that entirely. Each and every person has dignity—the good society is one which allows the thriving of all persons, especially the weak and vulnerable."
And yet, Smith pointed out, "the common good" challenges the libertarian stream of conservatism as well: "Individualists only want to see each individual live as they please, as long as they don't obstruct the ability of other individuals to do the same. They don't think anything is 'common,' except whatever minimal infrastructures are needed to create equal opportunity."
Focusing on the common good has another positive effect, Smith noted: It can both draw Christians into engagement with the wider society and prevent that engagement from becoming "all about politics." Essential to the common good, all the way back through Aquinas to Aristotle, has been the insight that the best forms of human flourishing happen in collectives that are smaller than, and whose origins are earlier than, the nation-state. Family above all, but also congregations, guilds, and clubs—these "private associations," with all their particular loyalties, paradoxically turn out to be essential to public flourishing. If we commit ourselves to the common good, we must become more public in our thinking and choices, and at the same time not too public. The common good is sustained most deeply where people know each other's names and faces—especially when it comes to the care of the vulnerable, who need more than policies to flourish.