- These arguments suppose that complete compatible collections of properties always define objects, some of which are real--namely those that have the simple property of existence--and the others of which are unreal.
- We first assume that there is an object which is that than which nothing greater can be thought.
- If it doesn't exist, then we could imagine adding to this object the property of existence, and then we'd get a greater object.
- So the object must already have the property of existence.
Problem (basically due to Oppy): Take a particular unicorn. This is defined by a complete compatible collection of properties. Now, replace non-existence with existence. We either get an incompatible or a compatible collection. If incompatible, unicorns are impossible, and I shall suppose they're possible. Suppose compatible. Then they are not complete--for if they were complete, then we'd have a complete compatible collection of properties that includes existence, and hence unicorns would exist.