175. Term: Metaphysics

Definition: The branch of philosophy concerned with the most general features of reality (being, causation, modality, time, identity, and dependence).

176. Term: Ontology

Definition: The subfield of metaphysics focused on what exists and what kinds of things exist.

177. Term: Existence

Definition: The status of being; in metaphysics, debates often concern what it means to exist and what sorts of entities exist.

178. Term: Causality

Definition: The relation between causes and effects; explanations often appeal to causal structure or dependence.

179. Term: Explanation

Definition: An account of why something is the case; in philosophy this includes causal explanation and non‑causal (for example, grounding) explanation.

180. Term: Brute fact

Definition: A fact posited to have no further explanation (it is taken as basic).

181. Term: Principle of Sufficient Reason (PSR)

Definition: A family of principles asserting that every fact has an explanation or reason why it is so rather than otherwise.

182. Term: Grounding

Definition: A non‑causal metaphysical dependence relation: facts about one level (for example, mental) may obtain in virtue of facts about another (for example, physical).

183. Term: Infinite regress

Definition: An explanatory or dependence chain that continues without termination; often debated whether such regresses are vicious or benign.

184. Term: Metaphysical necessity

Definition: A modality stronger than physical necessity: what could not have been otherwise given the nature of things (often modeled with □).

185. Term: Contingency

Definition: The modal status of being able to be otherwise; contingent facts are true in some possible worlds and false in others.

186. Term: Determinism

Definition: The thesis that, given the past and the laws, there is only one possible future course of events.

187. Term: Indeterminism

Definition: The denial of determinism: the laws and past do not fix a unique future; multiple futures may be compatible with identical prior conditions.

188. Term: Free will

Definition: A family of views about agency and control; commonly, the capacity to choose or act in a way that grounds moral responsibility.

189. Term: Compatibilism

Definition: The view that free will (or the freedom needed for responsibility) is compatible with determinism.

190. Term: Incompatibilism

Definition: The view that free will is incompatible with determinism.

191. Term: Libertarianism (free will)

Definition: An incompatibilist view holding that free will exists and therefore determinism is false (often requiring indeterministic agency).

192. Term: Counterfactual

Definition: A conditional about what would be the case if something were different (for example, ‘If I had chosen otherwise, …’).

193. Term: Nothingness

Definition: A philosophical topic concerning absence, non‑being, and the coherence of ‘nothing’ (distinct from an empty set as a mathematical object).

194. Term: Absolute nothingness

Definition: The putative state in which there is nothing whatsoever—no objects, events, properties, laws, or facts.

195. Term: Absence

Definition: A way of speaking about what is not present (for example, ‘there is no milk’), often analyzed as a property of contexts or regions rather than a ‘thing’.

196. Term: Identity (numerical identity)

Definition: The relation each thing bears only to itself; a = b asserts that a and b are one and the same entity.

197. Term: Personal identity

Definition: The problem of what makes a person the same person over time (for example, bodily continuity, psychological continuity, or other criteria).