Metaphysics is the branch of philosophy that studies the fundamental nature of reality, including the first principles of: being or existence, identity and change, space and time, cause and effect, necessity, and possibility.
In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality.
The Ship of Theseus is a thought experiment about whether an object which has had all of its original components replaced remains the same object. According to legend, Theseus, the mythical Greek founder-king of Athens, rescued the children of Athens from King Minos after slaying the minotaur and then escaped onto a ship going to Delos. Each year, the Athenians commemorated this by taking the ship on a pilgrimage to Delos to honor Apollo. A question was raised by ancient philosophers: After several centuries of maintenance, if each individual part of the Ship of Theseus was replaced, one at a time, was it still the same ship?
In logic, philosophy and related fields, mereology is the study of parts and the wholes they form. Whereas set theory is founded on the membership relation between a set and its elements, mereology emphasizes the meronomic relation between entities, which—from a set-theoretic perspective—is closer to the concept of inclusion between sets.
Roderick Milton Chisholm was an American philosopher known for his work on epistemology, metaphysics, free will, value theory, and the philosophy of perception.
Philosophy of space and time is the branch of philosophy concerned with the issues surrounding the ontology and epistemology of space and time. While such ideas have been central to philosophy from its inception, the philosophy of space and time was both an inspiration for and a central aspect of early analytic philosophy. The subject focuses on a number of basic issues, including whether time and space exist independently of the mind, whether they exist independently of one another, what accounts for time's apparently unidirectional flow, whether times other than the present moment exist, and questions about the nature of identity.
Modal realism is the view propounded by philosopher David Lewis that all possible worlds are real in the same way as is the actual world: they are "of a kind with this world of ours." It is based on four tenets: possible worlds exist, possible worlds are not different in kind from the actual world, possible worlds are irreducible entities, and the term actual in actual world is indexical, i.e. any subject can declare their world to be the actual one, much as they label the place they are "here" and the time they are "now".
Perdurantism or perdurance theory is a philosophical theory of persistence and identity. The debate over persistence currently involves three competing theories—one three-dimensionalist theory called "endurantism" and two four-dimensionalist theories called "perdurantism" and "exdurantism". For a perdurantist, all objects are considered to be four-dimensional worms and they make up the different regions of spacetime. It is a fusion of all the perdurant's instantaneous time slices compiled and blended into a complete mereological whole. Perdurantism posits that temporal parts alone are what ultimately change. Katherine Hawley in How Things Persist states that change is "the possession of different properties by different temporal parts of an object".
Philosophical presentism is the view that only present entities exist. According to presentism, there are no past or future entities. In a sense, the past and the future do not exist for presentists—past events have happened and future events will happen, but neither exist at all since they do not exist now. Presentism is a view about temporal ontology that contrasts with eternalism—the view that past, present and future entities exist —and with no-futurism—the view that only past and present entities exist.
In metaphysics, the A series and the B series are two different descriptions of the temporal ordering relation among events. The two series differ principally in their use of tense to describe the temporal relation between events and the resulting ontological implications regarding time.
In philosophy, the term formal ontology is used to refer to an ontology defined by axioms in a formal language with the goal to provide an unbiased view on reality, which can help the modeler of domain- or application-specific ontologies to avoid possibly erroneous ontological assumptions encountered in modeling large-scale ontologies.
In philosophy, four-dimensionalism is the ontological position that an object's persistence through time is like its extension through space. Thus, an object that exists in time has temporal parts in the various subregions of the total region of time it occupies, just like an object that exists in a region of space has at least one part in every subregion of that space.
In contemporary metaphysics, temporal parts are the parts of an object that exist in time. A temporal part would be something like "the first year of a person's life", or "all of a table from between 10:00 a.m. on June 21, 1994 to 11:00 p.m. on July 23, 1996". The term is used in the debate over the persistence of material objects. Objects typically have parts that exist in space—a human body, for example, has spatial parts like hands, feet, and legs. Some metaphysicists believe objects have temporal parts as well.
In philosophy, mereological essentialism is a mereological thesis about the relationship between wholes, their parts, and the conditions of their persistence. According to mereological essentialism, objects have their parts necessarily. If an object were to lose or gain a part, it would cease to exist; it would no longer be the original object but a new and different one.
The B-theory of time, also called the "tenseless theory of time", is one of two positions regarding the temporal ordering of events in the philosophy of time. B-theorists argue that the flow of time is only a subjective illusion of human consciousness, that the past, present, and future are equally real, and that time is tenseless: temporal becoming is not an objective feature of reality. Therefore, there is nothing privileged about the present, ontologically speaking.
In philosophy, specifically in the area of metaphysics, counterpart theory is an alternative to standard (Kripkean) possible-worlds semantics for interpreting quantified modal logic. Counterpart theory still presupposes possible worlds, but differs in certain important respects from the Kripkean view. The form of the theory most commonly cited was developed by David Lewis, first in a paper and later in his book On the Plurality of Worlds.
Metaphysics is the branch of philosophy that investigates principles of reality transcending those of any particular science. Cosmology and ontology are traditional branches of metaphysics. It is concerned with explaining the fundamental nature of being and the world. Someone who studies metaphysics can be called either a "metaphysician" or a "metaphysicist".
Donald Cary Williams, usually cited as D. C. Williams, was an American philosopher and a professor at both the University of California Los Angeles and at Harvard University.
Katherine Jane Hawley (1971-2021) was a British philosopher specialising in metaphysics, epistemology, ethics, and philosophy of physics. Hawley was a professor of philosophy at the University of St Andrews. She was the author of How Things Persist, Trust: a Very Short Introduction, and How To Be Trustworthy. Hawley was elected a Fellow of Royal Society of Edinburgh in 2016, elected a Fellow of the British Academy in 2020, and she was the recipient of a Philip Leverhulme Prize (2003) and a Leverhulme Major Research Fellowship (2014–16).
Extended modal realism is a metaphysical theory developed by Takashi Yagisawa. It concerns the question of what it means that something is possible or necessary. Modal realism is the view that besides the actual world, there are many possible worlds. They exist as alternate versions of the actual world we live in. It contrasts with actualism, which holds that there is only one world: the actual world. Extended modal realism is a special form of modal realism. It includes the controversial thesis that there are not just possible worlds but also impossible worlds. An impossible world is a world that contains a contradiction. Extended modal realism understands modality as a dimension similar to space and time. In this sense, a regular object, like a tree or a car, is not just extended in space and time but also across possible and impossible worlds: some parts of it exist in the actual world and other parts exist in non-actual worlds. There is only one universe encompassing everything that is real in the widest sense: the actual, the possible, and the impossible.
