Reality is a central concept in metaphysics concerned with what is ultimately real and how the world is structured at its most fundamental level. Metaphysical inquiry into reality asks whether reality is entirely physical, whether mental or abstract entities are also real, how appearances relate to what actually exists, and whether different levels or kinds of reality can be distinguished. Questions about reality often connect with being, existence, substance, causation, mind, matter, space, and time, making the concept foundational to many other areas of metaphysical thought.