• He understands the claim that God exists.
• He does not believe that God exists.

Anselm's goal is to show that this combination is unstable. Anyone who understands what it means to say that God exists can be led to see that God does exist. On this view, the atheist is not just mistaken: his position is internally inconsistent.

What follows is an attempt to clarify the argument as it is presented in Chapter II of the Proslogium. The argument in Chapter III is rather different, and in some ways more interesting. After you have worked through this page, you might try to produce a similar gloss on the second argument. This will not be easy: the argument is notoriously complicated. But you might find it a useful exercise nonetheless.

Let's work through the argument as Anselm presents it.

Anselm writes:

This is Anselm's definition. We might paraphrase it as follows:

By "God" we mean an absolutely unsurpassable being, a being that cannot conceivably be improved upon.

As we've stressed, you do not need to agree that this is what the word "God" ordinarily means. Treat it as a stipulation. Clearly, if Anselm can establish the existence of a being of this sort, his conclusion would be of immense philosophical and theological significance.

This puts the question: Is there in fact a being with the properties our definition assigns to God?

This begins and ends straightforwardly. The fool understands the definition of God but denies that God exists. The first hint of strangeness comes in what seems to be a parenthetical remark: "what he understands is in his understanding". Anselm apparently proposes to treat the understanding or the mind as if it were a place, and to speak of things existing "in the understanding". Anselm's assumption here is that if I understand claims about God, then we may say that God exists in my understanding or in my mind.

Anselm here explains a distinction. It is one thing for an object to exist in my understanding, and another for me to understand it to exist. This is a familiar distinction, even if the terms are not familiar. Ghosts, trolls, flying saucers and the like are all things I can think about. We might say that I have ideas of these things; Anselm says that they exist in the understanding. Anselm's point is that in general there is a difference between saying that something exists in my understanding and saying that I understand (or believe) it to exist. Trolls exist in my understanding; but I do not understand them to exist.

Here Anselm applies the distinction he has just drawn to the case of God. The fool understands claims about God. So God - a being than which none greater can be conceived - exists in his understanding. Anselm means this to be an entirely uncontroversial claim.

This is the heart of the argument. The trick is to show that God cannot possibly exist in the understanding alone. Anselm begins by contrasting existing in the understanding with existing in reality. This by itself is not problematic. Trolls exist in the understanding alone; Bill Clinton exists both in the understanding and in reality; and no doubt there are things that exist in reality that do not yet exist in the understanding because no human being has ever managed to frame a thought about them. The picture seems to be as follows:

In the area marked A we have things that exist in the understanding alone; in the area marked B we have things that exist both in the understanding and in reality; and in the area marked C we have things that exist in reality but not in the understanding. (For obvious reasons, we cannot give any concrete examples of the last category.)

At this stage the fool has conceded that God exists in the understanding: so God belongs either in A or in B. Anselm now argues that God cannot exist in the understanding alone. The argument seems to proceed as follows.

(1) Suppose (with the fool) that God exists in the understanding alone.

(2) Given our definition, this means that a being than which none greater can be conceived exists in the understanding alone.

(3) But this being can be conceived to exist in reality. That is, we can conceive of a circumstance in which theism is true, even if we do not believe that it actually obtains.

(4) But it is greater for a thing to exist in reality than for it to exist in the understanding alone.

(5) Hence we seem forced to conclude that a being than which none greater can be conceived can be conceived to be greater than it is.

(6) But that is absurd.

(7) So (1) must be false. God must exist in reality as well as in the understanding.

This reading of the argument is amply confirmed by the final paragraph:

Therefore, if that than which nothing greater can be conceived exists in the understanding alone, the very being than which nothing greater can be conceived is one than which a greater can be conceived. But obviously this is impossible. Hence there is no doubt that there exists a being than which nothing greater can be conceived, and it exists both in the understanding and in reality.

This is a useful first pass at the argument. Now let's go over it and try to isolate its most fundamental assumptions. (I'll highlight the premises of the reconstructed argument in red.) Remember the argument's dialectical context. The aim is to refute the fool - or less tendentiously, the rational atheist. So what we want to know about these premises is whether the fool should accept them. There is first the definition:

Then there are some assumptions about the Fool's understanding.

Anselm now assumes a principle that he clearly regards as trivial.

From (a),(b) and (d) we may now infer:

(e) God exists in the understanding.

(Note: this is not a premise. It is an intermediate conclusion supported by a quick argument from premises we have already accepted.)

Anselm now employs a form of reasoning called reductio ad absurdum. This is a very useful technique. In a proof of this sort, we begin by assuming the opposite of what we want to prove. Then we derive a contradiction or an absurdity from this supposition. And from this we conclude that our original assumption was false. The general form of such an argument is as follows:

Suppose P

From P it follows that Q

But Q is absurd (self-contradictory).

Therefore P is false.

For Anselm the target of his reduction is the proposition that God exists in the understanding alone. So let us suppose that this is the case:

(f) Suppose that God exists in the understanding but not in reality.

From (f) and (c) we may now infer

(g) God in fact exists in the understanding alone, but he may be conceived to exist in reality as well as in the understanding.

At this point Anselm wields what is perhaps his most controversial premise. It is hard to know exactly how to formulate it. But something like the following seems to be what Anselm has in mind.

The idea seems to be: if we compare two things that are alike in all respects except that one exists in the understanding alone and the other exists in reality, then the one that exists in reality is clearly greater, better, more perfect. We will have to discuss the cogency of this assumption in class. But suppose for now that it is granted. We may then argue as follows. From (g) and (h) it follows that

(I) God can be conceived to be greater than it actually is.

But this is absurd. For given our definition (a), this just means that

(j) A being that cannot be conceived to be greater than it is can be conceived to be greater than it is.

From which it follows that our supposition (f) is false. We may therefore conclude

(k) God exists in reality.

Now you should ask: Is this a valid argument as it stands? Are the assumptions plausible? Would the fool be willing to grant them? Would you be willing to grant them? If you think that the argument is not a good one, you are under an obligation to say where it goes wrong. It might go wrong in several places. See how many "mistakes" you can find.