Mereological universalism holds that any collection of entities constitutes a whole, even if the entities are otherwise unrelated. Various theories of the mereological principles underlying composition have been proposed. For example, David Lewis’s modal realism asserts that there exist countless spatiotemporally unified possible worlds, each just as real as the actual https://www.zumospin.net/ world. A different view suggests that reality is made up of many worlds that exist in parallel to one another, each representing a distinct way of how things could have been. In a narrow sense, being contrasts with becoming, and denotes stable or permanent aspects of reality. Some philosophers, such as Alexius Meinong, hold that being is a broader concept than reality, encompassing nonexistent objects, such as merely possible or incomplete objects, in addition to real or actual ones.
Inspired by Leibniz, David Lewis (1941–2001) developed modal realism, maintaining that possible worlds are as real as the actual world. E. Moore (1873–1958) drew on common sense and empirical science to oppose idealism, emphasizing that the world exists independently of the mind. Responding to Kant’s philosophy, the German idealists sought a unifying principle as the foundation of all reality. In Hindu philosophy, the school of Advaita Vedanta emerged in the 8th century and held that the world of everyday appearances is an illusion, contrasting it with the ultimate reality of Brahman. Inspired by Plato’s realm of forms, Plotinus (c. 204 – c. 270 CE) identified the One as the supreme principle underlying all of reality. His student Aristotle (384–322 BCE) proposed a system of ten categories describing the fundamental constituents of reality.
For example, one view suggests that macroscopic objects, such as a chair, depend on the microscopic objects that underlie them, such as elementary particles. The structure of reality concerns the fundamental patterns of being, describing how entities are organized and interact with each other. According to a common view, concrete objects exist in space and time, such as a flower, a horse, and a ship. Events are proposed constituents of reality that occur in time, such as the discovery of penicillin and the Second World War.

• Epistemology, another philosophical subdiscipline, explores how people can know reality.
• In a broad sense, appearances are not limited to what people perceive but can also include memories, beliefs, and thoughts.
• It focuses on how things seem to be, distinguishing real appearances, which are as they seem, from illusory ones, which are not as they seem.
• Various criteria for distinguishing real from unreal entities have been proposed, including causal powers, mind-independence, and being non-illusory.
• Some philosophers, such as Alexius Meinong, hold that being is a broader concept than reality, encompassing nonexistent objects, such as merely possible or incomplete objects, in addition to real or actual ones.

Realism and anti-realism

Accordingly, worldviews address not only theoretical matters but also practical and evaluative outlooks about what matters and how one should act. Another view maintains that they are real as digital objects with genuine existence and causal powers, residing within and being constituted by computational processes. Similarly, virtual reality worlds may incorporate real-world objects into the simulation or be entirely virtual.l Although it is not a widely accepted position, various thought experiments undermining the reliability of human cognitive faculties are discussed in the academic literature. It denies the existence of knowledge in any form or domain, arguing that knowledge is impossible. These limitations indicate a gap whereby reality is not fully captured and exceeds knowledge.

• Scientific realism is the view that the best scientific theories provide an accurate description of a mind-independent world.
• It is often contrasted with appearance, opposing what is with what seems to be, although the accuracy and fundamentality of this contrast are disputed.
• Realists hold that values are objective features of reality, meaning that there are mind-independent facts about whether something is good or bad, irrespective of subjective beliefs or personal preferences.
• Some outlooks suggest that only the fundamental level is ultimately real, arguing that non-fundamental entities are in some sense eliminable since reality can be described without them.
• Formalism, another form of anti-realism, understands mathematics as a practice of symbol manipulation, suggesting that mathematical truth is grounded in whether the manipulation rules permit the construction of a proof.
• Testimony is a transmission of knowledge from one person to another through communication.k
• It comprises beliefs, ideas, and attitudes that form a background against which people interpret experiences, make decisions, and navigate life.

For example, the laws of thermodynamics describe how heat and other forms of energy behave, such as the idea that the total amount of energy is always conserved. Existence monism contrasts with existence pluralism, which aligns more closely with everyday experience by asserting that reality is made up of many objects. There are different ways to conceptualize the relation between fundamental and non-fundamental entities, including the ideas of ontological dependence, metaphysical grounding, reduction, supervenience, and emergence. Another structural feature concerns the idea that some entities depend on, or are grounded in, other entities.

Realism and anti-realism

Naturalism argues that values are part of the natural world and can be studied by the natural sciences through empirical observation. Some positions concern the existence of values in general, while others are limited to specific domains, such as moral, aesthetic, or religious values. Formalism, another form of anti-realism, understands mathematics as a practice of symbol manipulation, suggesting that mathematical truth is grounded in whether the manipulation rules permit the construction of a proof. According to conventionalism, the truth of mathematical statements rests on linguistic conventions or definitions, rather than on their relation to language-independent reality.
It overlaps with the cognitive sciences, which investigate how cognitive processes transform information about the world, and with neuroscience, which studies the brain activities underlying such processes. It concerns the question of how mental and linguistic entities, such as thoughts and words, can establish contact with reality by successfully referring to things in the world. It focuses on how individuals experience reality and how conscious states are intentional or directed towards entities other than themselves. Epistemology, another philosophical subdiscipline, explores how people can know reality. They examine what it means for something to be real, how entities are divided into different categories of being, and which entities exist at the most fundamental level.

Values

In a broad sense, appearances are not limited to what people perceive but can also include memories, beliefs, and thoughts. Unreal entities, by contrast, depend for their existence on thoughts and ideas; they would not arise or would vanish without the mental activity creating or sustaining them. A related topic concerns the possibility and limits of knowledge as a successful cognitive contact with reality. Anti-realism, by contrast, holds that certain aspects of reality depend on mental processes, subjective perspectives, or social conventions.

Levels of reality

Anti-realism about abstract objects in mathematics takes various forms, including, but not limited to, fictionalism. Anti-realists hold that there are no abstract objects and offer alternative explanations. Realists and anti-realists about abstract objects debate whether, or in what sense, such entities form part of reality. Nominalism, another anti-realist view, rejects both mental and non-mental interpretations of universals. For example, a person may be a realist about universals and an anti-realist about values. In this sense, realism and anti-realism encompass many domain-specific positions across diverse fields.

On this view, higher levels show greater complexity and new phenomena but depend on the lower ones and could not exist without them. Some philosophical approaches rely on the idea of fundamentality and dependence to analyze the world in terms of levels or layers, such as material, biological, psychological, and social reality. In the Hindu tradition, it is often identified with Brahman as the all-pervasive reality and the supreme principle grounding all being. Some outlooks suggest that only the fundamental level is ultimately real, arguing that non-fundamental entities are in some sense eliminable since reality can be described without them.
This view emphasizes that reality is encountered, rather than invented, and can resist or frustrate beliefs and desires, unlike malleable imaginary creations. Another influential proposal treats mind-independence as a criterion of reality, arguing that real entities do not depend on how people think about them. The Eleatic principle is controversial because it is typically taken to deny that abstract objects studied in fields like mathematics, such as numbers, are real. However, stories about Santa Claus, such as written texts in children’s books, are part of reality since they can influence how people think. Discussed in ancient Greek philosophy as the Eleatic principle, it states that to be real is to be able to produce changes and to be affected by them. Criteria of reality are proposed features or standards that distinguish real entities from unreal ones.

It comprises beliefs, ideas, and attitudes that form a background against which people interpret experiences, make decisions, and navigate life. By contrast, Arthur Schopenhauer (1788–1860) criticized German idealism and held that a blind, irrational will is the underlying principle of reality. Immanuel Kant (1724–1804) rejected the possibility of objective knowledge of the things in themselves, arguing instead that all experience is shaped by the innate structures of human cognition. Plato (c. 427 – c. 347 BCE) argued for the existence of a realm of eternal forms or ideas in addition to the material world of mutable entities.
It holds that this practice can be useful in some contexts without ascribing substantive or framework-independent reality to such entities. Relativism, another form of anti-realism, holds that what counts as real varies based on one’s perspective or conceptual framework. Phenomenalism, a related view, reduces physical objects to collections of actual or possible sensory experiences. In the broadest sense, realism is the view that the external world and its constituents exist as they do regardless of how people perceive or think about them.
For example, psychologism asserts that mathematical objects are mental constructions or ideas rather than abstract objects. Fictionalists argue that discourse about abstract objects concerns fictional entities within make-believe frameworks. According to conceptualism, universals exist in the mind as concepts through which people categorize and order their impressions, acting as tools of cognitive organization rather than properties of external entities. Platonism about universals holds that they are part of reality in their own right, independent of the particular entities that instantiate them.