The Great Chain of Being is the title of a book by the American philosopher and historian of ideas A. O. Lovejoy (1873–1962), in which he explored the Neoplatonic and medieval notion of a hierarchy of actual existent things, ordered from the lowest, up through all possible intermediate gradations, including men, angels, and eventually culminating in God. The great literary celebration of this kind of hierarchy is the Divina Commedia of Dante. The notion connects to the view that it would be an inexplicable defect in the created universe if any real possibilities went unactualized. See also plenitude, sufficient reason.