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 grounding 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 ).
Realism 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. 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.
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, 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. Potentially the most extreme form of anti-realism is
solipsism — the belief that oneself is the only thing in existence.
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
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. Existential
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; 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 [worlds] complex enough to contain self-aware substructures [they] will 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 image of distant galaxies illustrates a challenge to understanding reality at any given instant: the light from these stars was emitted billions of years ago and many of these stars have moved, merged, or evolved since then. 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
evolution are central to the
system-building metaphysics of
A. N. Whitehead and
Charles Hartshorne.
Possible worlds The term "possible world" goes back to
Leibniz's theory of possible worlds, used to analyse necessity,
possibility, and similar
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
infinite 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 modal 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 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" 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
Leibniz's
Monadology,
Descartes's
Dualism,
Spinoza's
Monism.
Hegel's
Absolute idealism and
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?"
Phenomenology On a much broader and more subjective level, private experiences, curiosity, inquiry, and the selectivity involved in personal interpretation of events shapes reality as seen by one and only one person and hence is called
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
spiritual occurs on this level of reality. 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 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" 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". 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).
Skeptical hypotheses 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
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
filters. •
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. == Non-western philosophy ==