In the year 1078 a monk named Anselm of Canterbury astonished the world by
arguing that if it is even possible that God exists then it follows logically
that God does exist. Anselm's argument came to be called the ontological
argument, and it has sharply divided philosophers ever since. The 19th century
German philosopher Arthur Schopenhauer called it a charming joke, but many
prominent twentieth century philosophers such as Charles Hartshorne,
Norman Malcolm, and Alvin Plantinga think that it's sound. Here it is. God can be
defined as a maximally great being. If something were greater than God, then
that being would be God. And in order to be maximally great, a maximally great
being would have to be all-powerful, all-knowing, and morally perfect in every
possible world. Possible worlds are simply ways the world could have been. To
say that something exists in a possible world is just to say that if the world
were that way, then the thing would have existed. For example, even though unicorns
don't exist in the actual world, it seems at least possible that they could have,
so we can say that unicorns exist in some possible world. On the other hand, a
married bachelor does not exist in any possible world because the idea of a
married bachelor is logically incoherent. It could not possibly exist. So if it is
possible that a maximally great being exists, then we can say that he exists in
some possible world. But wait; a maximally great being would
not really be maximally great if it existed in only some possible worlds. To
be maximally great it has to be all-powerful, all-knowing, and morally
perfect in every possible world. So think about it; if a maximally great being
exists in any possible world, then it exists in every possible world, and if it
exists in every possible world, then it exists in the actual world. That is, a
maximally great being actually exists. Thus the atheist has to maintain not
simply that God does not exist, but that it is impossible that God exists. Here's
a summary of the ontological argument. Steps 2 through 6 are straightforward
and largely uncontroversial, but what about point number 1? Clearly if it can
be shown that the idea of a God is logically incoherent, then the argument
fails, but is the idea of a maximally great being absurd, like a married
bachelor or a square circle or the smell of blue? This doesn't seem to be the case.
The notion of the all-powerful, all-knowing, morally perfect being that
exists in every possible world seems to be a perfectly coherent idea. But
couldn't we parody this argument and make it work for anything? Why not say
it's logically possible that a maximally great pizza exists, therefore a maximally
great pizza does exist? However the idea of a maximally great pizza is not like
the idea of a maximally great being. In the first place,
there aren't intrinsic maximal values that make pizzas great. There could
always be one more pepperoni to increase its greatness. It's not even obvious what
properties make a pizza great: thin crust or thick crust, extra cheese, anchovies?
It's relative to the taste of the consumer. In the second place, a maximally
great pizza would have to exist in every logical possible world,
but that would mean that it couldn't be eaten, so it wouldn't really be a pizza
because a pizza is something you can eat. The idea of a maximally great pizza
turns out not to be a coherent idea. The idea of God, on the other hand, is an
intuitively coherent idea. Therefore, his existence is a possibility. And the
ontological argument shows that if God possibly exists, then God actually exists.