Having proved God exists and is not a deceiver, Descartes turns next to considering "whether anything certain is to be had concerning material things." (87)
He turns to "ideas of these things, insofar as they exist in my thought". He finds distinct ideas of length, breadth and depth; size; shape; position and motion. (87)
But that's not all: "I [distinctly] perceive countless particulars concerning shapes, number, movement and the like."
Of these, he says that "even if perhaps they do not exist anywhere outside me, [they] still cannot be said to be nothing." (88)
An Example: "when I imagine a triangle, even if perhaps no such figure exists outside my thought anywhere in the world and never has, the triangle still has a certain determinate nature, essence, or form which is unchangeable and eternal, which I did not fabricate, and which does not depend on my mind." (88)
Do we see here "a basis for an argument proving the existence of God?" (88)
"I have become accustomed to distinguishing existence from essence" (89)
Therefore, God exists.
The Ontological Argument Again (Slowly)
Reconstructing the Ontological Argument:
P1: God is the greatest conceivable being
i.e., a being whose essence includes all perfections (i.e., all 'great making properties').P2: We have the idea of God
P3: Existence is a perfection.
Now, assume P4: the essence of God does not include existence
i.e., God doesn't exist.P5: We can conceive of a greater being that God (from P3 & P4)
i.e., one whose essence includes all the same things as God's plus existence.P6: We can conceive of a being that is greater than the greatest conceivable being. (from P1 & P5)
Something must have gone wrong somewhere, but what?
Either, we’re wrong to think that those premises lead us to this conclusion (but that doesn’t seem to be the case - the argument appears to be valid) or else one of the premises is incorrect – Anselm and Descartes think the best choice is P4. Thus they conclude P4 is false.
What sort of argument are Descartes and Anselm presenting here?
i.e., God exists*******************
Some Objections to the Ontological Argument
1. Attempted Reductios: Can we use this same argument to prove that other perfect things must exist? In Anselm's day, a monk named Gaunilo suggested that we could use the same argument to prove that the perfect island (that island which is greater than all other islands) must exist. Can we also prove the existence of the prefect ice cream cone, the perfect gorilla, etc.? If so, isn't that enough to provide a reductio ad absurdum of the ontological argument.
A response: But all the argument shows is that if the perfect island doesn’t exist, it would be a greater thing if it did exist. It doesn’t say it would be a greater island.2. Does God really exist 'in our minds'?
So, then are we uttering a contradiction when we say that it is possible that the greatest conceivable island might not exist? In other words, is it contradictory to say that the greatest conceivable island does not have existence as part of its essence?
Imagine something that is omnipotent. Can it create a boulder so large it cannot lift it? If it can, then there’s something it can’t do (i.e., lift the boulder). If it can’t, there’s also something it can’t do (i.e., create the unliftable boulder). Perhaps omnipotence is incoherent.
Kant famously objected that existence isn’t a property at all (and so,
certainly not a great making property). Instead, Kant claimed that existence
was what a thing had to have before it had any properties at all.
Descartes on whether existence is a property: "I do not see what sort of thing you want existence to be, nor why it cannot be said to be a property just like omnipotence – provided, of course, that we take the word 'property' to stand for any attribute, or for whatever can be predicated of a thing; and this is exactly how it should be taken in this context." (Fifth Set of Replies, AT VII 382-3)