Editing Reality (section)

== Western philosophy ==
Philosophy addresses two different aspects of the topic of reality: the nature of reality itself, and the relationship between the [[mind]] (as well as [[language]] and culture) and reality.

On the one hand, [[ontology]] is the study of being, and the central topic of the field is couched, variously, in terms of being, existence, "what is", and reality. The task in ontology is to describe the most general [[category of being|categories of reality]] and how they are interrelated. If a philosopher wanted to proffer a positive definition of the concept "reality", it would be done under this heading. As explained above, some philosophers draw a distinction between reality and existence. In fact, many analytic philosophers today tend to avoid the term "real" and "reality" in discussing ontological issues. But for those who would treat "is real" the same way they treat "exists", one of the leading questions of [[analytic philosophy]] has been whether existence (or reality) is a property of objects. It has been widely held by analytic philosophers that it is ''not'' a property at all, though this view has lost some ground in recent decades.

On the other hand, particularly in discussions of [[Objectivity (philosophy)|objectivity]] that have feet in both [[metaphysics]] and epistemology, philosophical discussions of "reality" often concern the ways in which reality is, or is not, in some way ''dependent upon'' (or, to use fashionable [[jargon]], "constructed" out of) mental and cultural factors such as perceptions, beliefs, and other mental states, as well as cultural artifacts, such as religions and [[political movement]]s, on up to the vague notion of a common cultural [[world view]], or {{lang|de|[[Weltanschauung]]}}.

=== Realism ===
The view that there is a reality independent of any beliefs, perceptions, etc., is called [[Philosophical realism|realism]]. More specifically, philosophers are given to speaking about "realism ''about''" this and that, such as realism about universals or realism about the external world. Generally, where one can identify any class of object, the existence or essential characteristics of which is said not to depend on perceptions, beliefs, language, or any other human artifact, one can speak of "realism ''about''" that object.

A [[correspondence theory]] of knowledge about what exists claims that "true" knowledge of reality represents accurate correspondence of statements about and images of reality with the actual reality that the statements or images are attempting to represent. For example, the [[scientific method]] can [[Empiricism|verify]] that a statement is true based on the observable evidence that a thing exists. Many humans can point to the [[Rocky Mountains]] and say that this [[mountain range]] exists, and continues to exist even if no one is observing it or making statements about it.

===Anti-realism===
One can also speak of ''anti''-realism about the same objects. ''Anti-realism'' is the latest in a long series of terms for views opposed to realism. Perhaps the first was [[idealism (philosophy)|idealism]], so called because reality was said to be in the mind, or a product of our ''ideas''. [[Berkeleyan idealism]] is the view, propounded by the Irish [[empiricism|empiricist]] [[George Berkeley]], that the objects of perception are actually ideas in the mind. In this view, one might be tempted to say that reality is a "mental construct"; this is not quite accurate, however, since, in Berkeley's view, perceptual ideas are created and coordinated by God. By the 20th century, views similar to Berkeley's were called [[phenomenalism]]. Phenomenalism differs from Berkeleyan idealism primarily in that Berkeley believed that minds, or souls, are not merely ideas nor made up of ideas, whereas varieties of phenomenalism, such as that advocated by [[Bertrand Russell|Russell]], tended to go farther to say that the mind itself is merely a collection of perceptions, memories, etc., and that there is no mind or soul over and above such [[mental event]]s. Finally, anti-realism became a fashionable term for ''any'' view which held that the existence of some object depends upon the mind or cultural artifacts. The view that the so-called external world is really merely a social, or cultural, artifact, called [[social constructionism]], is one variety of anti-realism. [[Cultural relativism]] is the view that [[social issues]] such as morality are not absolute, but at least partially [[cultural artifact]].

=== Being ===
The nature of [[being]] is a perennial topic in metaphysics. For instance, [[Parmenides]] taught that reality was a single unchanging Being, whereas [[Heraclitus]] wrote that all things flow. The 20th-century philosopher [[Heidegger]] thought previous philosophers have lost sight of the question of Being (qua Being) in favour of the questions of beings (existing things), so he believed that a return to the Parmenidean approach was needed. An [[ontological catalogue]] is an attempt to list the fundamental constituents of reality. The question of whether or not [[existence]] is a [[wikt:predicate|predicate]] has been discussed since the Early Modern period, not least in relation to the [[ontological argument for the existence of God]]. Existence, ''that'' something is, has been contrasted with ''[[essence]]'', the question of ''what'' something is.
Since existence without essence seems blank, it associated with [[nothingness]] by philosophers such as Hegel. [[Nihilism]] represents an extremely negative view of being, the [[absolute (philosophy)|absolute]] a positive one.

=== Perception ===
The question of [[direct realism|direct or "naïve" realism]], as opposed to [[indirect realism|indirect or "representational" realism]], arises in the [[philosophy of perception]] and [[philosophy of mind|of mind]] out of the debate over the nature of [[Consciousness|conscious]] [[Qualia|experience]];<ref name=lehar>Lehar, Steve. (2000). [http://cns-alumni.bu.edu/~slehar/webstuff/consc1/consc1.html The Function of Conscious Experience: An Analogical Paradigm of Perception and Behavior] {{Webarchive|url=https://web.archive.org/web/20151021061139/http://cns-alumni.bu.edu/~slehar/webstuff/consc1/consc1.html |date=2015-10-21 }}, ''Consciousness and Cognition''.</ref><ref name=ce>Lehar, Steve. (2000). [http://sharp.bu.edu/~slehar/epist/naive-philos.html Naïve Realism in Contemporary Philosophy] {{webarchive|url=https://web.archive.org/web/20120811172229/http://sharp.bu.edu/~slehar/epist/naive-philos.html |date=2012-08-11 }}, ''The Function of Conscious Experience''.</ref> the [[Epistemology|epistemological]] question of whether the world we see around us is the real world itself or merely an internal perceptual copy of that world generated by [[neural]] processes in our brain. [[Naïve realism]] is known as ''direct'' realism when developed to counter ''indirect'' or representative realism, also known as [[epistemological dualism]],<ref>Lehar, Steve. [http://sharp.bu.edu/~slehar/Representationalism.html Representationalism] {{webarchive|url=https://web.archive.org/web/20120905185905/http://sharp.bu.edu/~slehar/Representationalism.html |date=2012-09-05 }}</ref> the philosophical position that our conscious experience is not of the real world itself but of an internal representation, a miniature [[Virtual reality|virtual-reality]] replica of the world.

[[Timothy Leary]] coined the influential term [[Reality tunnel|Reality Tunnel]], by which he means a kind of [[representative realism]]. The theory states that, with a subconscious set of mental filters formed from their beliefs and experiences, every individual interprets the same world differently, hence "Truth is in the eye of the beholder". His ideas influenced the work of his friend [[Robert Anton Wilson]].

=== Abstract objects and mathematics ===
The status of [[Abstraction (mathematics)|abstract]] entities, particularly numbers, is a topic of discussion in mathematics.

In the philosophy of mathematics, the best known form of realism about numbers is [[Platonic realism]], which grants them abstract, immaterial existence. Other forms of realism identify mathematics with the concrete physical universe.

Anti-realist stances include [[formalism (mathematics)|formalism]] and [[mathematical fictionalism|fictionalism]].

Some approaches are selectively realistic about some mathematical objects but not others. [[Finitism]] rejects [[Infinity|infinite]] quantities. [[Ultra-finitism]] accepts finite quantities up to a certain amount. [[Constructivism (mathematics)|Constructivism]] and [[intuitionism]] are realistic about objects that can be explicitly constructed, but reject the use of the [[principle of the excluded middle]] to prove existence by [[reductio ad absurdum]].

The traditional debate has focused on whether an abstract (immaterial, intelligible) realm of numbers has existed ''in addition to'' the physical (sensible, concrete) world. A recent development is the [[mathematical universe hypothesis]], the theory that ''only'' a mathematical world exists, with the finite, physical world being an illusion within it.

An extreme form of realism about mathematics is the [[mathematical multiverse hypothesis]] advanced by [[Max Tegmark]]. Tegmark's sole postulate is: ''All structures that exist mathematically also exist physically''. That is, in the sense that "in those [worlds] complex enough to contain self-aware substructures [they] will subjectively perceive themselves as existing in a physically 'real' world".<ref name="Tegmark2008">{{cite journal|last=Tegmark |first=Max |date=February 2008 |title=The Mathematical Universe |journal=Foundations of Physics |volume=38 |issue=2 |pages=101–150 |doi=10.1007/s10701-007-9186-9 |arxiv=0704.0646|bibcode = 2008FoPh...38..101T |s2cid=9890455 }}</ref><ref>Tegmark (1998), p. 1.</ref> The hypothesis suggests that worlds corresponding to different sets of initial conditions, physical constants, or altogether different equations should be considered real. The theory can be considered a form of [[Platonism]] in that it posits the existence of mathematical entities, but can also be considered a [[philosophy of mathematics|mathematical monism]] in that it denies that anything exists except mathematical objects.

=== Properties ===
{{Main|Problem of universals}}

The problem of universals is an ancient problem in metaphysics about whether [[Universal (metaphysics)|universals]] exist. Universals are general or abstract qualities, characteristics, [[property (philosophy)|properties]], kinds or [[relation (philosophy)|relations]], such as being male/female, solid/liquid/gas or a certain colour,<ref>Loux, Michael J. (2001). "The Problem of Universals" in ''Metaphysics: Contemporary Readings'', Michael J. Loux (ed.), N.Y.: Routledge, pp.&nbsp;3–13, [4]</ref> that can be predicated of individuals or particulars or that individuals or particulars can be regarded as sharing or participating in. For example, Scott, Pat, and Chris have in common the universal quality of ''being human'' or ''humanity''.

The realist school claims that universals are real&nbsp;– they exist and are distinct from the particulars that instantiate them. There are various forms of realism. Two major forms are [[Platonic realism]] and [[Aristotelian realism]].<ref>[[H. H. Price|Price, H. H.]] (1953). "Universals and Resemblance", Ch. 1 of ''Thinking and Experience'', Hutchinson's University Library, among others, sometimes uses such Latin terms.</ref> ''Platonic realism'' is the view that universals are real entities and they exist independent of particulars. ''Aristotelian realism'', on the other hand, is the view that universals are real entities, but their existence is dependent on the particulars that exemplify them.

[[Nominalism]] and [[conceptualism]] are the main forms of anti-realism about universals.

=== Time and space ===
{{Main|Philosophy of space and time}}

A traditional realist position in ontology is that time and space have existence apart from the human mind. [[Idealism|Idealists]] deny or doubt the existence of objects independent of the mind. Some [[anti-realism|anti-realists]] whose ontological position is that objects outside the mind do exist, nevertheless doubt the independent existence of time and space.

[[Immanuel Kant|Kant]], in the ''[[Critique of Pure Reason]]'', described time as an ''[[A priori and a posteriori|a priori]]'' notion that, together with other ''a priori'' notions such as [[space]], allows us to comprehend [[empirical evidence|sense experience]]. Kant denies that either space or time are [[Substance theory|substance]], entities in themselves, or learned by experience; he holds rather that both are elements of a systematic framework we use to structure our experience. Spatial [[measurement]]s are used to [[quantity|quantify]] how far apart [[Physical body|objects]] are, and temporal measurements are used to quantitatively compare the interval between (or duration of) [[Spacetime#Basic concepts|events]]. Although space and time are held to be ''transcendentally ideal'' in this sense, they are also ''empirically real'', i.e. not mere illusions.

Idealist writers such as [[J. M. E. McTaggart]] in ''[[The Unreality of Time]]'' have argued that time is an illusion.

As well as differing about the reality of time as a whole, metaphysical theories of time can differ in their ascriptions of reality to the [[past]], present and [[future]] separately.
* [[Presentism (philosophy of time)|Presentism]] holds that the past and future are unreal, and only an ever-changing present is real.
* The [[block universe]] theory, also known as Eternalism, holds that past, present and future are all real, but the passage of time is an illusion. It is often said to have a scientific basis in [[Theory of relativity|relativity]].
* The [[growing block universe]] theory holds that past and present are real, but the future is not.

Time, and the related concepts of process and [[evolution]] are central to the [[system-building metaphysics]] of [[A. N. Whitehead]] and [[Charles Hartshorne]].

=== Possible worlds ===
{{Main|Possible world}}
The term "possible world" goes back to [[Gottfried Wilhelm Leibniz|Leibniz's]] theory of possible worlds, used to analyse necessity, [[Logical possibility|possibility]], and similar [[modal logic|modal notions]]. [[Modal realism]] is the view, notably propounded by [[David Kellogg Lewis]], that all [[possible worlds]] are as real as the actual world. In short: the actual world is regarded as merely one among an [[infinity|infinite]] [[set theory|set]] of [[logically possible]] worlds, some "nearer" to the actual world and some more remote. Other theorists may use the Possible World framework to express and explore problems without committing to it ontologically. Possible world theory is related to [[alethic logic]]: a proposition is ''necessary'' if it is true in all possible worlds, and ''possible'' if it is true in at least one. The [[many worlds interpretation]] of quantum mechanics is a similar idea in science.

=== Theories of everything (TOE) and philosophy ===
{{Main|Theory of everything (philosophy)}}

The philosophical implications of a physical TOE are frequently debated. For example, if philosophical [[physicalism]] is true, a physical TOE will coincide with a philosophical theory of everything.

The [[System-building metaphysics|"system building"]] style of metaphysics attempts to answer ''all'' the important questions in a coherent way, providing a complete picture of the world. [[Plato]] and [[Aristotle]] could be said to be early examples of comprehensive systems. In the early modern period (17th and 18th centuries), the system-building ''scope'' of philosophy is often linked to the rationalist ''method'' of philosophy, that is the technique of deducing the nature of the world by pure ''a priori'' reason. Examples from the early modern period include the [[Gottfried Leibniz|Leibniz]]'s [[Monadology]], [[René Descartes|Descartes]]'s [[Mind-body dualism|Dualism]], [[Baruch Spinoza|Spinoza]]'s [[Monism]]. [[Georg Wilhelm Friedrich Hegel|Hegel]]'s [[Absolute idealism]] and [[Alfred North Whitehead|Whitehead]]'s [[Process philosophy]] were later systems.

Other philosophers do not believe its techniques can aim so high. Some scientists think a more mathematical approach than philosophy is needed for a TOE, for instance [[Stephen Hawking]] wrote in ''[[A Brief History of Time]]'' that even if we had a TOE, it would necessarily be a set of equations. He wrote, "What is it that breathes fire into the equations and makes a universe for them to describe?"<ref>as quoted in [Artigas, ''The Mind of the Universe'', p.123]</ref>

=== Phenomenology ===
On a much broader and more subjective level,{{Specify|date=August 2011}} private experiences, curiosity, inquiry, and the selectivity involved in personal interpretation of events shapes reality as seen by one and only one person<ref>"Present-time consciousness",
Francisco J. Varela,
''Journal of Consciousness Studies'' 6 (2-3):111-140 (1999)</ref> and hence is called [[Phenomenology (philosophy)|phenomenological]]. While this
form of reality might be common to others as well, it could at times also be so unique to oneself as to never be experienced or agreed upon by anyone else. Much of the kind of experience deemed [[Spirituality|spiritual]] occurs on this level of reality.<ref>
For the concept of "levels of reality", compare: {{cite book |url=https://books.google.com/books?id=TD90EAAAQBAJ |title=Levels of Reality in Science and Philosophy: Re-examining the Multi-level Structure of Reality |date=8 June 2022 |publisher=Springer Nature |isbn=9783030994259 |editor-last1=Ioannidis |editor-first1=Stavros |series=Jerusalem Studies in Philosophy and History of Science |publication-place=Cham, Zug |access-date=31 May 2024 |editor-last2=Vishne |editor-first2=Gal |editor-last3=Hemmo |editor-first3=Meir |editor-last4=Shenker |editor-first4=Orly |editor-link4=Orly Shenker}} 
</ref>

Phenomenology is a [[philosophical method]] developed in the early years of the twentieth century by [[Edmund Husserl]] (1859–1938) and a circle of followers at the universities of [[Göttingen]] and [[Munich]] in Germany. Subsequently, phenomenological themes were taken up by philosophers in France, the United States, and elsewhere, often in contexts far removed from Husserl's work.

The word ''phenomenology'' comes from the [[Greek language|Greek]] ''phainómenon'', meaning "that which appears", and ''lógos'', meaning "study". In Husserl's conception, phenomenology is primarily concerned with making the structures of consciousness, and the [[phenomena]] which appear in acts of consciousness, objects of systematic reflection and analysis. Such reflection was to take place from a highly modified "[[First-person narrative|first person]]" viewpoint, studying phenomena not as they appear to "my" consciousness, but to any consciousness whatsoever. Husserl believed that phenomenology could thus provide a firm basis for all human [[knowledge]], including [[scientific knowledge]], and could establish philosophy as a "rigorous science".<ref>{{cite book |author=Kockelmans |first=Joseph |author-link=Joseph Kockelmans |title=Edmund Husserl's phenomenology |publisher=[[Purdue University]] Press |year=2001 |isbn=1-55753-050-5 |edition=2 |pages=311–314}}</ref>

Husserl's conception of phenomenology has been criticised and developed by his student and assistant [[Martin Heidegger]] (1889–1976), by [[existentialists]] like [[Maurice Merleau-Ponty]] (1908–1961) and [[Jean-Paul Sartre]] (1905–1980), and by other philosophers, such as [[Paul Ricoeur]] (1913–2005), [[Emmanuel Levinas]] (1906–1995), and [[Dietrich von Hildebrand]] (1889–1977).<ref>{{cite book |author=Crowell |first=Steven Galt |title=Husserl, Heidegger, and the space of meaning: paths toward transcendental phenomenology |publisher=[[Northwestern University]] Press |year=2001 |isbn=0-8101-1805-X |page=160}}
</ref>

=== Skeptical hypotheses ===
[[File:braininvat.jpg|thumb|upright=1.3|A [[brain in a vat]] that believes it is walking]]
Skeptical hypotheses in philosophy suggest that reality could be very different from what we think it is; or at least that we cannot prove it is not. Examples include:
* The "[[Brain in a vat]]" hypothesis is cast in scientific terms. It supposes that one might be a disembodied brain kept alive in a vat, and fed false sensory signals. This hypothesis is related to the Matrix hypothesis below.
* The "[[Dream argument]]" of Descartes and [[Zhuang Zhou|Zhuangzi]] supposes reality to be indistinguishable from a dream.
* Descartes' [[Evil demon]] is a being "as clever and deceitful as he is powerful, who has directed his entire effort to misleading me."
* The [[five minute hypothesis]] (or [[omphalos hypothesis]] or [[Last Thursdayism]]) suggests that the world was created recently together with records and traces indicating a greater age.
* Diminished reality refers to artificially diminished reality, not due to limitations of sensory systems but via artificial [[Filter (signal processing)|filters]].<ref>{{cite journal |last1=Mori |first1=Shohei |last2=Ikeda |first2=Sei |last3=Saito |first3=Hideo |title=A survey of diminished reality: Techniques for visually concealing, eliminating, and seeing through real objects |journal=IPSJ Transactions on Computer Vision and Applications |date=28 June 2017 |volume=9 |issue=1 |pages=17 |doi=10.1186/s41074-017-0028-1 |s2cid=21053932 |issn=1882-6695|doi-access=free }}</ref>
* [[The Matrix (franchise)|The Matrix]] hypothesis or [[Simulated reality hypothesis]] suggest that we might be inside a [[computer simulation]] or [[virtual reality]]. Related hypotheses may also involve simulations with signals that allow the inhabitant species in virtual or simulated reality to perceive the external reality.