Metaphysics (from the Greek words μετά (metá) (“beyond” or “after”) and φυσικά (physiká) (“physics”)) is philosophy or philosophic thought about the nature of reality: what IS, and its properties.

For example: the world appears to contain many “things” – physical objects (like apples) are called particulars, and possess properties (or universals). There are also non-physical abstract objects, like numbers – and properties themselves can be considered abstract objects.

Ontology is the the study of existence: Rene Descarte proposed, “Cogito ero sum” (I think therefore I am).