• ontology - the metaphysical study of the nature of being and existence
  • metaphysics - the philosophical study of being and knowing
  • epistemology - the philosophical theory of knowledge
  • a priori - derived by logic without observed facts
  • a posteriori - derived from observed facts
  • rationalism - the philosophical doctrine that knowledge is acquired by reason without resorting to experience
  • empiricism - the philosophical doctrine that knowledge derives from experience
  • relativism - the philosophical doctrine that all criteria of judgement are relative to the individuals and situations involved

From Wikipedia:

Ontological perspectives

Social scientists adopt a number of approaches to ontology. Some of these are:

  • Realism - the idea that facts are “out there” just waiting to be discovered;
  • Empiricism - the idea that we can observe the world and evaluate those observations in relation to facts;
  • Positivism - which focuses on the observations themselves, attending more to claims about facts than to facts themselves;
  • Grounded theory - which seeks to derive theories from facts;
  • Engaged theory - which moves across different levels of interpretation, linking different empirical questions to ontological understandings;
  • Postmodernism - which regards facts as fluid and elusive, and recommends focusing only on observational claims.

https://en.wikipedia.org/wiki/Ontology