  The previous objection is related to another difficulty raised by Caterus. In order to illustrate that the inference from the mental to the extra-mental commits a logical error, critics have observed that if such inferences were legitimate then we could proliferate ontological arguments for supremely perfect islands, existing lions, and all sorts of things which either do not exist or whose existence is contingent and thus should not follow a priori from their concept. The trick is simply to build existence into the concept. So, while existence does not follow from the concept of lion as such, it does follow from the concept of an “existing lion.”