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:

1. if you think of this squid it will appear
2. you are thinking of that squid
3. 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.