Below is a summary of one of the more famous versions of the Ontological Argument, that of Saint Anselm of Canterbury in his Proslogium. This is very similar to Descartes' version of the Ontological Argument in his Meditations, which will be discussed in lecture. You can read an electronic version of Anselm's argument here; you can read an electronic copy of Descartes' Meditations here.
One of the allures of the Ontological Argument is primarily due to the fact that it claims to be a priori. That is, it attempts to prove God's existence by reason alone, independent of experience. Roughly, the thought behind the argument is that just by contemplating our idea of God--without having to look out in the world or find any sort of empirical proof--we can come to conclude that God must exist.
Another interesting feature of this argument is that it has the form of a reductio ad absurdum. This means that it begins with an assumption that is precisely contrary to what it sets out to prove--consequently, the argument begins by supposing that God does not exist. From this assumption, the strategy is then to show that a contradiction or absurdity logically follows, in which case we must reject the original supposition and accept its contrary--namely, that God does exist.
(For more on a priori and reductio arguments, go to my logic page here.)
(II) Summary of Argument
Think of God as the greatest conceivable being, or as "something than which nothing greater can be conceived." To get a grasp on this, take every great-making attribute you like--wisdom, power, knowledge, moral goodness, etc.--amplify it to its limit, and there you've got God. If you can think of anything greater than what you've just thought of, then you haven't succeeded in thinking about the thing than which nothing greater can be conceived.
Notice that just thinking of such a being does not (yet!) commit you to thinking that such a being exists. For consider: even if you think that such a 'greatest conceivable being' does not exist, you at least have the ability to understand or have an idea of what such a being would be like. That is, you can, at the very least, understand what such a being would be like. And this is all the argument needs to get it going: so long as you can at least understand the idea of a greatest conceivable being, it will be shown that such a being must exist.
Existing in the Mind vs. Existing in Reality
Next, we need to make sense of the difference between existing in the mind and existing in reality. Intuitively, many things can exist in the mind alone without existing in reality. For example, unicorns, wizards, and the fountain of youth are all things that exist in the mind alone, but do not exist in reality. In contrast, there might be some things that exist in reality, but do not exist in the mind. For instance, there could be some totally crazy looking beetle that has not yet been thought of in the minds of men, but nonetheless exists in the world. So there are some things that exist in the mind alone, that need not exist in reality; and there are some things that exist in reality, that need not exist in the mind.
Setting Up the Reductio
Let's suppose that the Greatest Conceivable Being exists in the mind alone, but not in reality. This might seem a really backwards way to the conclusion--after all, this is an argument for the existence of God. That is, this is an argument to the conclusion that God exists in reality, as well as in the mind. But this is the nature of a reductio ad absurdum. One assumes the contrary of what one is trying to prove in order to show that a contradiction or absurdity follows. So this argument will start out assuming that the Greatest Conceivable Being exists in the mind alone, but not in reality.
Existing in Reality Makes Things Greater!
A crucial premise in the Ontological Argument is the claim that existing in reality is a great-making property. Intuitively, this isn't such a crazy claim. For consider: Suppose we have an imagined beer that exists in the mind alone. Make this pint of beer anything you like--make it as cold as you like, as bitter or hoppy as you like, etc.--but make sure that it exists in the mind alone, and not in reality. Nice, right? But not of much good to us, if we were thirsty for a cold one. But now compare this merely imagined beer to one that's not only imagined, but one that actually exists. That is, we want to consider the situation where our beer not only exists in the mind, but exists in reality as well. Presumably, it is better that the pint of beer exists in reality, as well as in the mind, rather than the beer existing in the mind alone. At least, it's pretty clear which one you'd prefer given that you've got a considerable thirst. So, intuitively, things that exist in reality, as well as in the mind, are greater than things that exist in the mind alone.
Showing an Absurdity Follows
To recapitulate, we have assumed that the Greatest Conceivable Being
exists in the mind alone, and not in reality. But we have also agreed
a thing that exists in reality, as well as in the mind, is greater than
a thing that exists in the mind alone. At this point, we're in trouble!
For we can now think of a being greater than the Greatest Conceivable
one that exists. Thus, the Greatest Conceivable Being--the being than
nothing greater can be conceived--is a being than which something
greater can be conceived. This is a contradiction! Therefore,
original assumption--that the Greatest Conceivable Being exists in the
mind alone--must be false, and it's contrary must be true. That is, the
Greatest Conceivable Being must exist in reality as well as in the
(III) Formalizing the Argument
1. Suppose that the Greatest Conceivable Being
in the mind, but not in reality. [Let's call this imaginary being Rod.]
2. Existence in reality is greater than existence in the mind alone.
3. We can conceive a Greatest Conceivable Being that exists in reality as well as in the mind. [Let's call this being Todd]
4. Therefore, there is a being [Todd] that is greater than the Greatest Conceivable Being [Rod].
5. But this is a contradiction: there cannot be a being greater than the Greatest Conceivable Being.
6. Therefore, it is false that the Greatest Conceivable Being exists in the mind alone and not in reality. And, since we have already agreed that the
Greatest Conceivable Being at least exists in the mind, it must exist in reality as well. So: GOD EXISTS!
Guanilo suggests that something has seriously gone awry in the Ontological Argument. To show this, he devises a similar argument, resulting in a conclusion that we know to be false. He suggests that we run a parallel argument with one minor alteration--replace the Greatest Conceivable Being with the Greatest Conceivable Island. The replacement argument can be formalized in the following way:
1. Suppose that the Greatest Conceivable Island
in the mind, but not in reality. [Let's call this imaginary island
2. Existence in reality is greater than existence in the mind alone.
3. We can conceive a Greatest Conceivable Island that exists in reality as well as in the mind. [Let's call this island Maud.]
4. Therefore, there is a island [Maud] that is greater than the Greatest Conceivable Island [Ned].
5. But this is a contradiction: there cannot be an island greater than the Greatest Conceivable Island.
6. Therefore, it is false that the Greatest Conceivable Island exists in the mind alone and not in reality. And, since we have already agreed that the
Greatest Conceivable Island at least exists in the mind, it must exist in reality as well. So: The Greatest Conceivable Island EXISTS!
Guanilo's point is that if the Ontological Argument goes through,
we should be able to reason similarly for the greatest conceivable island.
Indeed, we presumably should be able to run it for the greatest
the greatest conceivable lover, the greatest conceivable beer, the
conceivable evil being, etc. Yet since it is clear that there is no
conceivable island, lover, beer, evil being, etc., something is amiss
"BUT, you say, it is as if one should suppose an island in the ocean, which surpasses all lands in its fertility, and which, because of the difficulty, or the impossibility, of discovering what does not exist, is called a lost island; and should say that the be no doubt that this island truly exists in reality, for this reason, that one who hears it described easily understands what he hears.
Now I promise confidently that if any man shall devise anything existing either in reality or in concept alone (except that than which a greater be conceived) to which he can adapt the sequence of my reasoning, I will discover that thing, and will give him his lost island, not to be lost again.
But it now appears that this being than which a greater is inconceivable cannot be conceived not to be, because it exists on so assured a ground of truth; for otherwise it would not exist at all."
Immanuel Kant objects that "existence" is not a predicate in the way that "red", "six feet tall", and "wacky" are. For example, if someone says "the castle is blue", the speaker is attributing a property--blueness--to the castle. Yet when you say "the castle exists", you are not, strictly speaking, attributing anything to the castle. Rather, you are saying that the castle is instantiated, or exists in the world. In other words, we aren't really adding anything to our idea of the castle, but to our idea of the world, and the way that it is--namely, that it is such that the castle is in it.
To illustrate the above point, consider the following examples.
1. Consider a table. Now abstract away all of its properties except existence. That is, imagine that you could leave it existing without all of its other properties: color, shape, size, function, and so on. But what is the difference between existence alone and nothing at all?
2. Lisa and Jane are both compiling lists of the qualities of the perfect mate so that they can each put an add in the personals. Since Lisa and Jane have similar tastes, they both end up with the following add: "Intelligent, hot chick in search of good-looking male, with an affinity for doling out compliments, playing pool til dawn, and talking philosophy until the cows come home." In fact, the only respect in which Jane's ad differs from Lisa's is that Jane has supplemented the forgoing blurb with the extra qualification: "and must exist." Now, is Jane's ad really any better than Lisa's? No. Moreover, Jane has misunderstood the purpose if the list, which is to set forth the qualities of a perfect mate. It is another matter whether these qualities are exemplified in an actual guy. Jane and Lisa can decide what they want to put into their description of the perfect guy, but the world decides whether anybody meets such a description.
3. We cannot simply build existence into our
of things, yet it seems we have no problem doing this with regular
For example, suppose we define a a unicorn as "a one horned magical
that exists." One might then claim that unicorns exist. But, of course,
this is just a verbal trick. Nothing but the world can determine
something fitting our concepts exists or not, and wishing it doesn't
it so. Contrast this, however, with regular predicates. If I define
as someone who drinks heavily and smells funny, then we can
claim that smelloozers drink heavily and smell funny. So we can build
into our definitions, but not existence. So, existence must not be a
Notice that the strategy of this objection is to indirectly attack
the truth of premise 2 (existence in reality is greater than
existence in the mind alone). For an underlying assumption of the truth
of premise 2 is that existence is a predicate like 'blue', 'round' and
'groovy' are. So, unlike Guanilo's objection, which attacks
the form of
the Ontological Argument, Kant's objection attacks the truth of one of
the premises (viz., premise 2).
3. Inconceivability Objection
Consider the series of positive integers: 1, 2, 3, etc. Now suppose
I ask you to imagine the greatest conceivable integer. Rightly
you should be a bit dumbfounded, as it is quite obvious that the
integers are not the sort of thing that admit of a "greatest" member.
is, for any integer you can think of, there will always be one greater.
(In fact, there will always be infinitely many integers greater than
one you have in mind.) In this way, the Greatest Conceivable Integer is
an impossible object. This objection claims that the idea of the
Conceivable Being is like the idea of the Greatest Conceivable
Like Kant's objection, the strategy of this objection is to
undermine the truth of one of the premises--viz., premise 1. The truth
of premise one relies on our ability to at least conceive or imagine
the greatest conceivable being. But if the Inconceivability objection
correct, then we cannot conceive or imagine the Greatest Conceivable
Being, and hence, we won't be able to make the supposition--premise
1--that gets the whole reductio going in the first place.
Put another way: we know what it takes for
be one thing or two when it (they) exist in reality (note: we will
hopefully be spending some time in class discussing this point, so
don't worry for now if it isn't so clear to you). But this isn't the
case with things that exist in the mind. For how are we to know
whether the pink elephant that one person understands and the pink
that another understands are one and the same elephant? Put in terms of
Qualitative and Quntitative (or Numerical) Identity:
Numerical identity is the
relation that each thing holds to itself--e.g., I am numerically
identical to myself, you are numerically identical to yourself, Jon
Stewart is identical to himself, etc. If x is numerically identical to y, then x and y are one in number; "they" are one.
Qualitative identity, on the other hand, is the relation that many things can have to many others, provided that they have the same properties in common. For example, in class I talked about how two markers could have many of the same properties--e.g., they could both be white on the outside, with a black felt tip, a black plastic cap, cylindrical in shape, so many inches long, kept in a cardboard box, etc.--yet since they are two markers they are not numerically identical. Rather, they merely share some of their properties, or qualities--they are qualitatively identical--but they are not one and the same, numerically identical, marker.
How are we to distinguish between merely qualitatively identical (or exactly similar) pink elephants that merely exist in the mind, from truly qunatitatively (or numerically) identical pink elephants that exist in the mind? Unless entities are extended in the world—unless they exist in reality—there seems to be no other sense in which ‘they’ can be, or exist.This objection would be another way to reject the truth of premise 2, since this premise presupposes that the distinction between existence in the mind and existence in reality is a legitimate one.
Saint Anselm, Proslogium.
William L. Rowe, "The Ontological Argument" in Reason and Responsibility, ed. Landau & Shafer-Landau.
Gideon Rosen, "Anselm's Ontological Argument," Rosen's webpage summary on the Ontological Argument.