The word ontology comes from Greek ov; meaning genitive, that which ‘is’ (being), and logia; meaning science, study, and/or theory.
Ontology is the study of that which is, the study of the way things are. The science, study, or theories of the form and nature of reality. Ontology is the study of being, the study of the nature of reality.
Ontology can be metaphysical and is considered the first branch of metaphysical philosophy. In this context, ontology can be thought of as the set of definitions used to describe an essential (fundamental) form of the particular reality being described.
i.e. when describing the ontology of positivist science one might list a posteriori observation, hypothesis testing, and other components of the scientific method as the fundamental components of science, or parts of the ontology of science.
Ontology can/might be:
- The study of the nature of existence.
- The specification of concept(s).
- The body of knowledge describing a domain of knowledge that is commonly known (for example through folklore or common sense).
Ontology is a “set-of-concept-definitions” Tom Gruber, Stanford University in a discussion on AI.
Ontology is the “metaphysical science or study of being,” 1660s (Gideon Harvey)
The word epistemology comes from the Greek word epistēmē; meaning empirical knowing. Epistemology is empirical, based on what can be known either by direct observation or accepted as measured by a reliable source.
Epistemology is the study of knowledge and knowing based on well justified belief.
- Epistemology is a meta view of science, the study of studying, the theory about how we theorize.
- Epistemology is the study of how we acquire knowledge.
Methodology is focused on the specific ways — the methods — that we can use to try to understand our world.