1. Ontology as the Study of Existence
Textbook presentations of what ontology is virtually always characterize it in terms of existence questions. This is true of both ‘classic’ and more recent presentations. Recall the opening sentences of Quine’s (1948: 21) “On What There Is”:
A curious thing about the ontological problem is its simplicity. It can be put in three Anglo-Saxon monosyllables: ‘What is there?’
More recent presentations by leading metaphysicians agree in essence. Here is van Inwagen (1998: 16):
One very important part of metaphysics has to do with what there is, with what exists. This part of metaphysics is called ontology. Ontology, that is, is the part of metaphysics that deals with metaphysical statements having general form like ‘An X exists’ and ‘There are Ys’.
And here is Sider (2007: 4):
Thus, we have very general ontological questions (existence questions) about objects… Other ontological questions include the question discussed above of whether properties exist, the question of whether numbers exist, and even the ‘metaontological’ question of what it means to investigate whether objects of a certain sort ‘really’ exist.
On this view, the goal of ontology is to produce a list of all things, in the broadest possible sense of ‘thing’—all entities, all quantifiabilia, all ontoids.