The Summa Theologiae is a work of astounding breadth and scope: five folio vol-umes of closely packed print, and more closely packed thought; incredibly, it was a work intended, not for the learned and wise, but for beginners. Walter Farrell, O.P., fully honors that intention with his four Companion volumes to the Summa, which together offer an easy guidebook to St. Thomas's greatest work. These are not simply more books about...