A Little History of Philosophy (Little Histories)

by Nigel Warburton

Anselm's argument, which he included in his book Proslogion, starts from the uncontroversial claim that God is that being ‘than which nothing greater can be conceived’. This is just another way of saying God is the greatest being imaginable: greatest in power, in goodness and in knowledge. Nothing greater can be imagined – or that thing would be God. God is the supreme being. This definition of God doesn't seem controversial: Boethius (see Chapter 7) defined God in a similar way, for example. In our minds, we can clearly have an idea of God. That too is uncontroversial. But then Anselm points out that a God that only existed in our minds but not in reality wouldn't be the greatest being conceivable. One that actually existed would certainly be greater. This God could conceivably exist – even atheists usually accept that. But an imagined God cannot be greater than an existing one. So, Anselm concluded, God must exist. It follows logically from the definition of God. If Anselm is right, we can be certain that God exists simply from the fact that we have an idea of God. This is an a priori argument, one that doesn't rely on any observation about the world to reach its conclusions. It is a logical argument that, from an uncontroversial starting point, seems to prove that God exists.