The most elusive and perhaps famous argument in the history of the philosophy of religion was put forth in the eleventh century by St Anselm. Now known as the ontological argument, it is based on the idea that God is that being greater than which is inconceivable. Although historically debate focused on the issue of whether existence is a property, or a perfection, required in our concept of such a being, recently it has taken a back seat to the examination of the indisputable attributes a perfect being must exemplify if He exists. Traditionally such attributes include: omnipotence, omniscience, omnibenevolence, immutability and so forth. The first challenge to the accepted attributes was posed in the Middle Ages; it is the oldest and probably the best known paradox in the philosophy of religion: Can God create a stone so heavy that even He cannot lift it? Whatever the answer is, apparently He is not Almighty. A slightly different version of the omnipotence paradox was advanced in 1955 by J. L. Mackie who questioned whether an omnipotent being could ‘make things He cannot subsequently control’.Both versions are intended to show that the concept of omnipotence suffers from internal incoherence and is therefore inapplicable to any being.