Reality

Reality is the sum or aggregate of all that is real or existent within a system, as opposed to that which is only imaginary. The term is also used to refer to the ontological status of things, indicating their existence. In physical terms, reality is the totality of a system, known and unknown.

Philosophical questions about the nature of reality or existence or being are considered under the rubric of ontology, which is a major branch of metaphysics in the Western philosophical tradition. Ontological questions also feature in diverse branches of philosophy, including the philosophy of science, philosophy of religion, philosophy of mathematics, and philosophical logic. These include questions about whether only physical objects are real (i.e., physicalism), whether reality is fundamentally immaterial (e.g. idealism), whether hypothetical unobservable entities posited by scientific theories exist, whether a 'God' exists, whether numbers and other abstract objects exist, and whether possible worlds exist. Epistemology is concerned with what can be known or inferred as likely and how, whereby in the modern world emphasis is put on reason, empirical evidence and science as sources and methods to determine or investigate reality.

Related concepts

World views and theories

A common colloquial usage would have ''reality'' mean "perceptions, beliefs, and attitudes toward reality", as in "My reality is not your reality." This is often used just as a colloquialism indicating that the parties to a conversation agree, or should agree, not to quibble over deeply different conceptions of what is real. For example, in a religious discussion between friends, one might say (attempting humor), "You might disagree, but in my reality, everyone goes to heaven."

Reality can be defined in a way that links it to worldviews or parts of them (conceptual frameworks): Reality is the totality of all things, structures (actual and conceptual), events (past and present) and phenomena, whether observable or not. It is what a world view (whether it be based on individual or shared human experience) ultimately attempts to describe or map.

Certain ideas from physics, philosophy, sociology, literary criticism, and other fields shape various theories of reality. One such belief is that there simply and literally ''is'' no reality beyond the perceptions or beliefs we each have about reality. Such attitudes are summarized in the popular statement, "Perception is reality" or "Life is how you perceive reality" or "reality is what you can get away with" (Robert Anton Wilson), and they indicate anti-realism – that is, the view that there is no objective reality, whether acknowledged explicitly or not.

Many of the concepts of science and philosophy are often defined culturally and socially. This idea was elaborated by Thomas Kuhn in his book ''The Structure of Scientific Revolutions'' (1962). '' The Social Construction of Reality'', a book about the sociology of knowledge written by Peter L. Berger and Thomas Luckmann, was published in 1966. It explained how knowledge is acquired and used for the comprehension of reality. Out of all the realities, the reality of everyday life is the most important one since our consciousness requires us to be completely aware and attentive to the experience of everyday life.

A priori and a posteriori

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 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 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 movements, on up to the vague notion of a common cultural world view, or .

The view that there is a reality independent of any beliefs, perceptions, etc., is called 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.

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, 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 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 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 events. 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.

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 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.

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 the question of Being (qua Being) in favour of the questions of beings (existing things), so 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 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 a positive one.

Perception

The question of direct or "naïve" realism, as opposed to indirect or "representational" realism, arises in the philosophy of perception and of mind out of the debate over the nature of conscious experience;Lehar, Steve. (2000)
The Function of Conscious Experience: An Analogical Paradigm of Perception and Behavior
, ''Consciousness and Cognition''.Lehar, Steve. (2000)

, ''The Function of Conscious Experience''. the 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, the philosophical position that our conscious experience is not of the real world itself but of an internal representation, a miniature virtual-reality replica of the world.

Timothy Leary coined the influential term 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 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 and fictionalism.

Some approaches are selectively realistic about some mathematical objects but not others. Finitism rejects infinite quantities. Ultra-finitism accepts finite quantities up to a certain amount. 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 orldscomplex enough to contain self-aware substructures heywill subjectively perceive themselves as existing in a physically 'real' world". 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 mathematical monism in that it denies that anything exists except mathematical objects.

Properties

The problem of universals is an ancient problem in metaphysics about whether universals exist. Universals are general or abstract qualities, characteristics, properties, kinds or relations, such as being male/female, solid/liquid/gas or a certain colour, 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 – 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. ''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

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

Kant, in the '' Critique of Pure Reason'', described time as an '' a priori'' notion that, together with other ''a priori'' notions such as space, allows us to comprehend sense experience. Kant denies that either space or time are 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 measurements are used to quantify how far apart objects are, and temporal measurements are used to quantitatively compare the interval between (or duration of) 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 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 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