For some philosophers, called 'deflationist', this question is linguistic, that is, it concerns the usage of expressions like 'At least one such-and-such exists'. Such phrases are called quantifier expressions.
For other philosophers, ontology concerns the actual existence of real things in the universe. The subject is complicated by discussion of issues like whether compound objects really exist, a question of mereology. For example, does a 'book' exist or only the 'pages' of the book. How do we draw the line between 'reasonable' compound objects and silly ones like 'my nose and the Eiffel tower'? Another confusion called 'Plato's beard' considers whether a statement like 'Pegasus is a flying horse' implies a belief in the existence of Pegasus. In general terms, is it true that statements, regardless of whether they are true, are about something? Another large arena for discussion is the existence of properties and other universals that appear to be instantiated in multiple objects, rather than a particular one, and their distinction from instances (tropes).
- Tony Lawson (December, 2004). A concept of ontology. Retrieved on 2013-07-19.
- Willard van Orman Quine (September, 1948). "On what there is". Review of metaphysics 2: p. 21 ff. Reprinted in Willard van Orman Quine (1980). “Chapter 1: On what there is”, From a logical point of view, 2nd. Harvard University Press. ISBN 0674323513. On-line version is found here.
- Eli Hirsch (2011). “Introduction”, Quantifier Variance and Realism: Essays in Metaontology. Oxford University Press, p. xii. ISBN 0199732116.
- Dag Westerståhl (April 19, 2011). Edward N. Zalta, ed.: Generalized Quantifiers. The Stanford Encyclopedia of Philosophy (Summer 2011 Edition).
- Hilary Putnam (1987). The Many Faces of Realism, 2nd. Open Court, p. 33. ISBN 0812690427.
- Alex Orenstein, Petr Kotatko (2001). “Plato's beard and Quine's stubble”, Knowledge, Language and Logic: Questions for Quine. Springer, p. 210. ISBN 140200253X.
- Swoyer, Chris and Orilia, Francesco (September 12, 2011). Edward N. Zalta, ed.: Properties. The Stanford Encyclopedia of Philosophy (Winter 2011 Edition).
- Bacon, John (Feb 27, 2008). Edward N. Zalta, ed.: Tropes. The Stanford Encyclopedia of Philosophy (Winter 2011 Edition).