This is just a set of notes about the subject, not yet well organized and far from exhaustive.
Existence is the ontological topic par excellence.
Hume and Kant , among others, are each well-known for their shared view that the claim that a thing exists, when added to our notion of a thing, does not add anything to the concept. For example, if we form a complete notion of Moses, and superadd to that notion the claim that Moses existed, we are not adding anything to the notion of Moses. But, as G. E. Moore pointed out in an early essay, it is a matter of some difficulty to say what exactly what this view amounts to. Similar claims, however, are not as often made on behalf of existence. That is, contemporary philosophers at least are wont to treat existence as a univocal, unambiguous concept, as if the only sense of 'existence', or the only sort of existence worth talking about, were the existence of physical objects .