 Philosophers and theologians have made numerous efforts to revive or demolish Anselm’s argument over the centuries. The most influential proponents include René Descartes, Gottfried Leibniz, Charles Hartshorne, Norman Malcolm, Robert M. Adams, and Alvin Plantinga. Its main detractors include Anselm’s contemporaneous interlocutor—a monk named Gaunilo—as well as Thomas Aquinas, Descartes’ correspondents Johannes Caterus, Marin Mersenne, and Antoine Arnauld, Immanuel Kant, and, more recently, David Lewis (1970), Peter van Inwagen (1977), and Graham Oppy (1996, 2009). In what follows, a number of the relevant moves in the early modern discussion will be considered, as well as some contemporary developments of the 17th century modal argument.