ABSTRACT
The ontological argument is an a priori argument for God’s existence which was rst formulated in the eleventh century by St Anselm, was famously defended by René Descartes in the seventeenth century, and still has important modern advocates, such as Alvin Plantinga. It has also had equally famous critics, such as Immanuel Kant in the eighteenth century and Gottlob Frege and Bertrand Russell in the nineteenth to twentieth centuries. To say that the argument is an a priori one is just to say that it is a deductive argument from premises whose truth is deemed to be knowable without recourse to empirical evidence of any kind. The argument has received many different formulations in the course of its long history, but St Anselm’s original version in his Proslogion of 1077/8 (chs. 2 and 3: see Charlesworth 1965) can be reconstructed in something like the following way:
1 God is, by de nition, a being than which none greater can be conceived. 2 A being than which none greater can be conceived exists at least in the
mind. 3 It is greater to exist in reality than to exist only in the mind. 4 Therefore, God – a being than which none greater can be conceived – exists not
only in the mind but also in reality.
