Everything in the context of Entity

Reality is the state of everything that exists, not how they might be imagined. Different cultures and academic disciplines conceptualize it in various ways.

Philosophical questions about the nature of reality, existence, or being are considered under the rubric of ontology, a major branch of metaphysics in the Western intellectual tradition. Ontological questions also feature in diverse branches of philosophy, including the philosophy of science, religion, mathematics, and logic. These include questions about whether only physical objects are real (e.g., physicalism), whether reality is fundamentally immaterial (e.g., idealism), whether hypothetical unobservable entities posited by scientific theories exist (e.g., scientific realism), whether God exists, whether numbers and other abstract objects exist, and whether possible worlds exist. Skeptics question whether any of those claims are true, and suggest more extreme postulates.

Nothing, no-thing, or no thing is the complete absence of anything, as the opposite of something and an antithesis of everything. The concept of nothing has been a matter of philosophical debate since at least the 5th century BCE. Early Greek philosophers argued that it was impossible for nothing to "exist". The atomists allowed nothing but only in the spaces between the invisibly small atoms. For them, all space was filled with atoms. Aristotle took the view that there exists matter and there exists space, a receptacle into which matter objects can be placed. This became the paradigm for classical scientists of the modern age like Isaac Newton. Nevertheless, some philosophers, like René Descartes, continued to argue against the existence of empty space until the scientific discovery of a physical vacuum.

Existentialists like Jean-Paul Sartre and Martin Heidegger (as interpreted by Sartre) have associated nothing with consciousness. Some writers have made connections between Heidegger's concept of nothing and the nirvana of Eastern religions.

Something and anything are concepts of existence in ontology, contrasting with the concept of nothing. Both are used to describe the understanding that what exists is not nothing without needing to address the existence of everything. The philosopher, David Lewis, has pointed out that these are necessarily vague terms, asserting that "ontological assertions of common sense are correct if the quantifiers—such words as "something" and "anything"—are restricted roughly to ordinary or familiar things."

The idea that "something" is the opposite of "nothing" has existed at least since it was proposed by the Neoplatonist philosopher Porphyry in the 3rd century. One of the most basic questions of both science and philosophy is: why is there something rather than nothing at all? A question that follows from this is whether it is ever actually possible for there to be nothing at all, or whether there must always be something.