1. Ontological arguments Concept of God: perfect being –God is supposed to be a perfect being. –That’s just true by definition. –Even an atheist can agree to this. “Yes, I agree, God is supposed to be a perfect being. It’s just that there is no such thing.” Perfection requires existence –If a being is perfect, then it must exist. –A nonexisting God would be more perfect if it existed. So God exists –Otherwise, you’d get a contradiction—a perfect being that doesn’t even exist and hence could be more perfect.

2. Anselm’s version Concept of God –“something than which nothing greater can be conceived” –i.e., the greatest conceivable being –This is Anselm’s version of God as a perfect being. –Even an atheist (“the fool”) can understand this. –The greatest conceivable being at least exists in thought, even if it doesn’t exist also in reality.

3. Anselm’s version Perfection requires existence –Suppose the atheist is right. Suppose that the greatest conceivable being exists only in thought (and not also in reality). –If so, then one could conceive of something even greater—something just like it that also exists in reality. –[Anselm seems to be assuming that it’s greater to exist than not to exist (or something similar) so that somehow perfection requires existence] So God exists –But it’s obviously a contradiction to have something conceivably greater than the greatest conceivable being. –So atheism leads to a contradiction.

4. Anselm’s version Extra bonus material! –Anselm goes on to argue that God’s nonexistence is inconceivable. –After all, “it is possible to conceive of a being which cannot be conceived not to exist; and this is greater than one which can be conceived not to exist” [emphasis added] –So, given that God is the greatest conceivable being, it follows that it’s impossible to conceive of God not existing.

5. Gaunilo’s reply The Lost Island example “Well then, you can no longer doubt that this island more excellent than all other lands really exists somewhere, since you do not doubt that it is in your mind; and since it is more excellent to exist not only in the mind but in reality as well, this island must necessarily exist, because if it didn't, any other island really existing would be more excellent than it, and thus that island now thought of by you as more excellent will not be such.” Parody –This reasoning looks highly suspicious and even ridiculous, but it seems to be an exact parallel to Anselm’s reasoning. –So (Gaunilo concludes) there must be something seriously wrong with Anselm’s reasoning.

6. Descartes’ version If I have an idea of x, then anything I clearly and distinctly perceive as belonging to x really does belong to x. –[Example: I have an idea of a triangle. And so, since I clearly and distinctly perceive the property HAVING ANGLES THAT ADD UP TO 180 DEGREES as belonging to it, it follows that this property really does belong to it.] I have an idea of God. So anything I clearly and distinctly perceive as belonging to God really does belong to God. I clearly and distinctly perceive the property ALWAYS EXISTING as belonging to God. Therefore, the property ALWAYS EXISTING really does belong to God. [That is, God really does exist] (So the truth of God’s existence is at least as certain as mathematical truths.)

7. Descartes’ version For most things, existence and essence are separate. –I don’t clearly and distinctly perceive existence as belonging to triangles, or other shapes or numbers. –That is, existence can be separated from the essence of a triangle. But, if I carefully focus on my idea of God, I see that existence is connected with God’s essence. –The property of having angles that add up to 180 degrees cannot be separated from the essence of a triangle. –The idea of a mountain [upward slope] cannot be separated from the idea of a valley [downward slope] –Likewise, the property of existing cannot be separated from the essence of God. It is a contradiction to think of God lacking existence. –Just as it is a contradiction to think of a mountain without a valley [or a triangle that doesn’t have angles adding up to 180 degrees]

8. Descartes’ version Here’s a clue: “it is... a contradiction to think of God (that is, a supremely perfect being) lacking existence (that is, lacking a perfection)” –Check out those parenthetical remarks! Descartes must think that existence is a perfection, and that it is a contradiction to think of God, a supremely perfect being, lacking a perfection. If so, then the argument is something like this: 1.(I c/d perceive that) existence is a perfection. 2.(I c/d perceive that) all perfections belong to God. 3.So (I c/d perceive that) existence belongs to God. 4.If I c/d perceive that something belongs to x, then it really does belong to x. 5.So existence belongs to God.

9. Johannes Caterus’ objections Two ways to read the conclusion: –Here’s Descartes’ conclusion: “The property ALWAYS EXISTING belongs to God” –Version 1: “The concept of God includes within it the concept of always existing” –Version 2: “God has the property of always existing” The problem: –The first conclusion might well follow from the argument, but it doesn’t say anything about the real world—even an atheist could agree to it. –The second conclusion does say something about the real world, but it doesn’t follow from the argument (not unless you simply assume that God really exists).

10. Johannes Caterus’ objections How he puts it: –“Even if it is granted that a supremely perfect being carries the implication of existence in virtue of its very title, it still does not follow that the existence in question is anything actual in the real world; all that follows is that the concept of existence is inseparably linked to the concept of a supreme being. So you cannot infer that the existence of God is anything actual unless you suppose that the supreme being actually exists; for then it will actually contain all perfections, including the perfection of real existence“

11. Johannes Caterus’ objections The “existing lion” objection –If Descartes’ reasoning is good, then we can give a priori demonstrations of the existence of lions. –All we have to do is take the property EXISTING and build it into the concept: instead of the concept lion, we have the concept existing lion. –Presumably we could do the same thing with unicorns and trolls and goblins. –Descartes’ argument does the same thing—it starts out with existence simply built into the concept of a perfect being. –Schopenhauer later wrote that a proponent of an ontological argument “takes care to include the predicate actuality or existence, either openly stated or wrapped up for decency’s sake in some other predicate, such as perfection, immensity, or something of the kind”

12. Pierre Gassendi’s objection Existence is not a perfection –When listing the characteristics of a triangle, you wouldn’t list EXISTENCE. –Similarly, you shouldn’t include existence as one of the perfections of God. –Existence isn’t a perfection; instead, it’s what’s needed beforehand in order to have any perfections in the first place—it’s a prerequisite for perfections.

13. Objections to ontological arguments Parodies –Gaunilo’s “Lost Island” –These don’t help us locate the problem. They just indicate that there must be some problem somewhere. Uninteresting conclusion –The conclusion looks like the full-blooded “God really exists”. –But it’s actually nothing more than the harmless “The concept of God includes existence” (which even an atheist could happily agree to).

14. Objections to ontological arguments Question-begging –God’s existence has been secretly smuggled into the very premises of the argument. –This ‘smuggling’ can be really obvious (“existing lion”) or less obvious (“perfect being”). Existence is different –It’s not a perfection. –It’s not a predicate. –It’s a necessary background condition for characteristics. It’s not itself a characteristic.

15. Modal versions Concept of God: necessary being –God is supposed to be a necessary being—a being that doesn’t just happen to exist, but has to exist, couldn’t possibly not exist. –This is true by definition. –Even an atheist can agree to this. God’s existence is possible –This seems intuitively plausible. –Even atheists will tend to admit that, even though God doesn’t actually exist, still God could have possibly existed, if things had been different. It follows that God actually exists(!)

16. Modal versions Necessary existence –With necessary beings, they can’t happen to exist or happen not to exist. –They can’t exist in some worlds and fail to exist in others. –If a necessary being does exist, it exists in all possible worlds. –If a necessary being doesn’t exist, it exists in no possible worlds.

17. Modal versions Possible existence –If something possibly exists, then there is at least some world where it exists. –So if God possibly exists, then there is at least some world where God exists. Actual existence –But since God is a necessary being, if God exists in some world, then God exists in all worlds. –So God exists in the actual world.

18. Modal versions The upshot –Atheists have to say that it’s impossible for God to exist (at least when God is understood to be a necessary being). –Theists, likewise, have to say that it’s impossible for God not to exist. Dogmatic? –This can sound dogmatic. –But the sort of possibility involved here isn’t connected to confidence or dogmatism. –You can say “I think it’s impossible for God not to exist, though of course I could be wrong”

19. Hume on ontological arguments A priori demonstrations –We’ve seen that Hume rejects the possibility of any a priori demonstration of God’s existence—or, indeed, anything’s existence. –Support for theism has to come from observation of the natural world. –This is because a priori demonstrations ought to make the other side inconceivable. –And God’s nonexistence is at least conceivable.

20. Hume on ontological arguments Necessary being –Hume has no room for any kind of necessity besides “being inconceivable any other way” –So 2+2=4 counts as necessary because it’s inconceivable any other way. –But then the notion of a necessary being is deeply flawed—after all, any being can be conceived not to exist.