The Philosophy of Reality

What Is

The philosophy of reality is the branch of philosophy that asks what exists, what it is for something to be real, and how the world appears to us relates to the world as it is. It is not the same as science, which investigates specific features of the world; it is the inquiry into the very framework within which any investigation takes place. When we ask whether time is real, whether numbers exist, whether consciousness is part of the physical world, or whether the future is fixed, we are doing the philosophy of reality.

The discipline has two main branches. Ontology asks what kinds of things exist: objects, properties, events, processes, facts, minds, numbers, possible worlds. Metaphysics, in its broadest sense, asks how those things hang together: what causation is, what laws are, what persistence through change consists in, and whether reality has a fundamental level. The two are intertwined, and the philosophy of reality is often used as a general name for both.

The classic framing of the subject is the contrast between appearance and reality. Ordinary experience presents a world of colors, sounds, and values; physics describes a world of fields and particles; and mathematics describes structures that seem not to be anywhere in particular. The philosophy of reality asks which of these descriptions, if any, is authoritative, and whether the manifest image and the scientific image can be unified.

Historical Background

The question "What is real?" is the oldest in philosophy. Plato argued that the changing objects of sense are not fully real: they are images or participants in eternal Forms, and only the Forms are true reality. Aristotle rejected this, holding that reality is the world of substances we encounter, and that universals exist in things rather than apart from them. The medieval debate between realism and nominalism about universals continued the argument about what kinds of things genuinely exist.

The early modern period reoriented the question around the mind. René Descartes distinguished mind and matter as two kinds of substance; John Locke distinguished the real essence of things from our ideas of them; and George Berkeley argued that to be is to be perceived, making reality mind-dependent. Immanuel Kant drew the famous line between the phenomenal world — the world as it appears under the forms of space, time, and the categories — and the noumenal world of things in themselves, which we cannot know.

The twentieth century transformed the debate again. Logical empiricists questioned whether the question of reality had any meaning beyond verification; Willard Van Orman Quine argued that the question of what exists is simply the question of what our best theories say exists; and the rise of physicalism made the scientific image the default standard of reality. At the same time, phenomenologists such as Edmund Husserl and Martin Heidegger argued that the reality of the lived world is prior to scientific abstraction, and that any account of reality that begins with objects detached from experience has already missed something essential.

Key Concepts

Ontology. The study of what exists and the categories of being. Standard questions include whether universals exist, whether events are real, whether there are possible worlds, and whether the future exists.

Metaphysical realism. The view that the world exists and has a determinate structure independent of human thought, language, or perception. It is opposed by various forms of idealism, relativism, and constructivism.

Idealism. The view that reality is fundamentally mental or mind-dependent. Berkeley's immaterialism is the classical version; Kant's transcendental idealism is the most influential modern version.

Physicalism. The view that everything that exists is physical, or that all facts are determined by the physical facts. It is the dominant metaphysical framework in contemporary philosophy of mind and science.

The manifest and scientific images. Wilfrid Sellars's influential contrast: the manifest image is the world as it appears to common sense — persons, colors, values — while the scientific image is the world as described by fundamental physics. The philosophy of reality asks how the two are related.

Existence and being. The most general question: what is it for something to exist? Philosophers distinguish existence as a property of individuals from existence as a quantifier, and ask whether existence is univocal across different kinds of things.

Contemporary Relevance

The philosophy of reality is not a relic of the past. It frames debates about consciousness: if physicalism is true, the hard problem of consciousness — how subjective experience arises from objective processes — is the central problem of the philosophy of mind. It frames debates about mathematics: do numbers exist independently of us, as mathematical Platonists hold, or are they constructions? It frames debates about time, free will, and causation that bear on physics and neuroscience. And it frames debates about values: are moral facts part of reality, as moral realists hold, or projections of our attitudes?

The question of reality also touches everyday life. When people ask whether the world is "real" — whether the future is fixed, whether the self is an illusion, whether meaning is invented or discovered — they are asking questions that the philosophy of reality has sharpened over two and a half millennia. The discipline does not always supply comfortable answers, but it supplies the clarity without which the questions cannot be properly asked.

Sources

1. van Inwagen, P. & Sullivan, M. (2020). "Metaphysics." Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/metaphysics/
2. Stoljar, D. (2021). "Physicalism." Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/physicalism/
3. Kraut, R. (2017). "Plato." Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/plato/
4. Miller, A. (2019). "Realism." Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/realism/
5. Hofweber, T. (2021). "Logic and Ontology." Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/logic-ontology/

Related Topics

• The meaning of the central term is examined in the discussions of what reality is and what metaphysics is.
• Whether consciousness fits within physical reality is the subject of the philosophy of mind; see also the discussion of the illusion of self.
• The reality of time, determinism, and the future connects the philosophy of reality to the free will debate.
• The Understanding Reality collection is devoted to the questions treated here.
• Plato, Kant, and Russell exemplify three major strategies: realism about Forms, transcendental idealism, and scientific realism.