Anselm’s Ontological Argument

What does "ontological" mean?

•         ontology =_def  the study of being, or what exists

Anselm's argument:

I can conceive of God, a perfect being.  But if God doesn’t exist, then God isn’t perfect.  So, God must exist.

(This is a highly compressed version of the argument.  Details to follow.)

Anselm’s starting point is to give a definition:

•         God =_def the greatest possible being. 

Anselm asks us to imagine God.  If we are truly imagining God, then what we imagine, he claims, must be something entirely unsurpassable in greatness (perfection).  For God, if God exists, must, by definition, be as excellent as anything possibly could be.  Accordingly, our concept of God is a concept of the being than which none greater is possible.

Consider the following division:

Possible things include both:

The question is:  In which of these categories do we place God? 

Anselm is going to try to show us that we must place God in the category of  "things which exist in reality").

Now for the ontological argument itself:

(1)  God is that than which nothing is greater.

(2)  God exists in the understanding (or, is possibly real).

(6)  So, something might be greater than that which nothing is greater.

  (7) But this is a contradiction, so our supposition (4) must be false.

(8) Therefore, God exists in reality.

But by premise 3 having existence is better than not having it. So only God₁, not God₀, could be God according to Anselm's definition (premise 1).

Notice that this argument is entirely a priori -- the conclusion is known by reasoning alone.  It is "evident to any rational mind," as Anselm puts it. 

Some classical objections:

(Are the premises true and are we warranted in believing them?  Is the logic correct?)

Focus on (3):   This premise assumes that existence is a great-making property.  For a thing that has the property of existing is greater than that same thing when it doesn’t have that property.

But:  Is existence really a property? 

Many think not.  For example, Immanuel Kant.  Consider an apple pie.  Suppose you give me a recipe for an apple pie.  Do you need to put “existence” on the list?  Kant says, “No, we don’t need to add it; we already have all the ingredients we need.” 

Here’s another way of making the same point.  Suppose I use your recipe to bake an apple pie.  Can we just say that we then have an apple pie?  Or do we need to say that we have an existing apple pie?  But it seems redundant to say that we have an existing apple pie.  So, existence is not a property of the apple pie.  Call this the redundancy objection.

Now a second objection.  A monk named Guanilo raised perhaps the most significant problem for the ontological argument.  What Guanilo did was argue that it must be unsound.  Why?  Because it can be used to prove all kinds of crazy things.  But an argument that proves all kinds of crazy things must be flawed in some way.

Guanilo applied Anselm’s reasoning to the greatest possible island -- the Isle of the Blest:

(1*)   The Isle of the Blest is the island than which none greater is possible.

(2*)   The Isle of the Blest exists in the understanding.
etc. (Exercise: construct the remainder of the counterproof.)

(8*)  Therefore, the Isle of the Blest exists in reality.

Of course, this is absurd.  We know that we can’t prove that a particular island exists through an a priori argument, by pure reasoning alone.  In order to find out, we have to go out and look for it (knowledge a posteriori, from experience),

If Guanilo is right, then there is something fundamentally wrong with Anselm’s reasoning.  But is God uniquely that being whose existence can be known a priori?