By parity of reasoning, the same logic would establish the existence of a maximally perfect island and an existent lion, since those ideas also include existence.

The objection aims to show that, like the idea God, the idea of the existent lion and the idea of the maximally perfect island include existence, and thus the existence of these objects can be established via an ontological argument. But the claim that the existence of Caterus’s lion and Gaunilo’s island can be established in this way is absurd, and thus the same holds for the theistic ontological argument. Note that this parity argument via a reductio ad absurdum, if successful, would show that