Existence

Existence is commonly held to be that which objectively persists independent of one's presence.Ontology is the philosophical study of the nature of being, existence or reality in general, as well as of the basic categories of being and their relations. Traditionally listed as a part of the major branch of philosophy known as metaphysics, ontology deals with questions concerning what entities exist or can be said to exist, (for instance: ""Does the stellar structure UDFj-39546284 exist?""), and how such entities can be grouped, related within a hierarchy, and subdivided according to similarities and differences. A lively debate continues about the existence of God.Epistemology studies criteria of truth, defining ""primary truths"" inherently accepted in the investigation of knowledge. The first is existence. It is inherent in every analysis. It is self-evident, a priori nature cannot be consistently doubted, since a person objecting to existence according to some standard of proof must implicitly accept the standard's existence as a premise.Materialism holds that the only thing that exists is matter, that all things are composed of material, and all phenomena (including consciousness) are the result of material interactions.Life is a characteristic that distinguishes objects that have self-sustaining biological processes from those that do not—either because such functions have ceased (death), or else because they lack such functions and are classified as ""inanimate"".