Ontology

The word ‘ontology’ is used to refer to philosophical investigation of existence, or being. Such investigation may be directed towards the concept of being, asking what ‘being’ means, or what it is for something to exist; it may also (or instead) be concerned with the question ‘what exists?’, or ‘what general sorts of thing are there?’ It is common to speak of a philosopher’s ontology, meaning the kinds of thing they take to exist, or the ontology of a theory, meaning the things that would have to exist for that theory to be true.