Arguments from Defining God into Existence
There is a certain class of arguments for the existence of God which involve simply defining him in such a way that he must exist. You can imagine the basic form of such an argument as applied to a squid which has the property that when anyone thinks of it, it magically appears in front of them. So:
- if you think of this squid it will appear
- you are thinking of that squid
- therefore it exists
The error with this line of argument is clear to see when applied to the squid or to Gaunilo's Perfect Island---it pre-supposes the existence of said squid. Yes, if such a squid existed then it would appear and would thus exist---if A then A. This tells us absolutely nothing though. A similar issue appears when using some sort of notion of "perfection"---"oh, if A is perfect then it must exist, because it would be deficient if it didn't exist." What this amounts to is saying "I define A as a magical dolphin with the property that it exists and can shoot lasers; therefore such a dolphin exists." The issue, again, is that it requires the existence of this dolphin---the properties you make up for any sort of creature in your head are irrelevant, what matters is which properties it has which relies on its prior existence. If such a dolphin does not exist, then its properties are completely irrelevant to any discussion, if it does then obviously it does---this shows nothing.