Well worth your time is this lecture, “Friendship and the Common Good,” by Fr. Aquinas Guilbeau, O.P., prior at the Priory of the Immaculate Conception in Washington, D.C., and professor of moral theology. Fr. Guilbeau presents not only an overview of the nature and context of De Koninck’s famous essay on the primacy of the common good, but shows the connection between the common good and friendship. The key to this connection is St. Thomas Aquinas’s doctrine of communicatio. More at the link!