---
title: Perception and Reality
sort: 110
section-id: epistemology
description: Direct realism, indirect realism, idealism, and phenomenalism — the major theories of perception and its relation to reality.
language: en
---

# Perception and Reality

Perception is our most immediate route to knowledge of the external world, and yet it is philosophically treacherous. We trust our senses — and then we discover that sticks look bent in water, towers look small from a distance, and the table that appears brown under incandescent light appears subtly different under daylight. These illusions and variations prompt an epistemological crisis: if our senses can mislead us, how can we trust them? And if we cannot fully trust them, what can we know about the world?

## The Argument from Illusion

The *argument from illusion* is a traditional challenge to naive perceptual realism. It proceeds roughly as follows ^[Ayer, A.J., *The Foundations of Empirical Knowledge*, Macmillan, 1940]:

1. In cases of illusion, what we are directly aware of (the bent stick, the shrunken tower) is not identical to the physical object.
2. Perceptual experience in veridical (non-illusory) cases is intrinsically similar to experience in illusory cases.
3. Therefore, what we are directly aware of even in veridical cases is not the physical object itself, but some intermediate object — a *sense datum*, a subjective representation, a mental image.

If this argument is correct, we never perceive the external world directly. We perceive representations of it, and must infer the world from those representations.

## Direct Realism

*Direct realism* (also called naïve realism or common-sense realism) holds that in ordinary perception, we are directly aware of the physical world. There are no intermediary mental objects standing between us and the things we perceive.

Contemporary direct realists reject the argument from illusion by contesting its first premise. When I see the bent stick, I am not aware of some private sense datum; I am aware of the stick itself, and my experience has the representational content that the stick is bent — which is a false content, but this does not require a separate object ^[Martin, M.G.F., "The Transparency of Experience", *Mind and Language* 17, 2002, pp.376-425].

**Disjunctivism** is a sophisticated variant of direct realism that draws a fundamental distinction between veridical experience and illusion/hallucination ^[McDowell, J., "Criteria, Defeasibility, and Knowledge", *Proceedings of the British Academy* 68, 1982]. On this view, there is no common factor between seeing a tree and hallucinating a tree. Veridical perception genuinely consists in being acquainted with the object; hallucination is a numerically distinct kind of event that merely mimics it. This dissolves the argument from illusion by denying that veridical and illusory experiences must have the same fundamental nature.

## Indirect Realism

*Indirect realism* (or representationalism) accepts that we never perceive the external world directly. Our direct objects of experience are mental representations — sense data, *qualia*, or "ideas" in the empiricist terminology. These representations are caused by, and typically resemble, the physical objects that produce them.

Locke is the canonical indirect realist in the early modern period ^[Locke, J., *An Essay Concerning Human Understanding*, 1689, Book II]. He distinguished *primary qualities* (extension, shape, motion, number) — features of objects that genuinely resemble our ideas of them — from *secondary qualities* (colour, taste, smell, temperature) — features that our ideas do not resemble; they are simply the powers of objects to produce certain experiences in us.

Indirect realism faces a significant epistemological challenge: if we only ever directly perceive our representations, how can we know that those representations accurately track the external world? Locke acknowledged this; Berkeley exploited it to devastating effect.

## Berkeley's Idealism

George Berkeley argued that indirect realism collapses into idealism ^[Berkeley, G., *A Treatise Concerning the Principles of Human Knowledge*, 1710]. If we only directly perceive ideas, and ideas are inherently mental, then matter — that supposed cause of ideas existing independently of all minds — is a philosopher's fiction. *Esse est percipi*: to be is to be perceived.

Berkeley was not denying the existence of the ordinary objects of experience — tables, trees, other people. He was claiming that their existence consists in their being perceived, either by finite minds or, when unobserved by us, by the mind of God. This is idealism, but of a commonsensical variety: Berkeley insisted his view was closer to common sense than Locke's.

The main objection to Berkeley is the arbitrariness of experience. If physical objects are collections of ideas, why do we not simply experience whatever we imagine? Berkeley's answer — the regularity of experience is guaranteed by God — is metaphysically expensive and not universally persuasive.

## Phenomenalism

*Phenomenalism* is a non-theistic descendant of Berkeley, associated with Hume, Mill, and twentieth-century logical empiricists like A.J. Ayer. Rather than reducing physical objects to ideas in God's mind, phenomenalism analyses statements about physical objects as equivalent to conditionals about what experiences would occur under certain conditions ^[Mill, J.S., *An Examination of Sir William Hamilton's Philosophy*, 1865; Ayer, A.J., *Language, Truth and Logic*, Gollancz, 1936].

"There is a table in the next room" is analysed as something like: "If anyone were to look in the next room under normal conditions, they would have table-experiences." The table is, in Mill's phrase, a "permanent possibility of sensation."

Phenomenalism faces serious difficulties with conditionals involving unfulfillable antecedents and with the enormous complexity required to capture ordinary physical-object claims in purely phenomenal terms. It has largely been abandoned as a research programme.

## Contemporary Debates

Current philosophy of perception engages with cognitive science and debates about the *format* of perceptual representation (is it propositional? imagistic? iconic?), the *reach* of perception (does it extend to abstract objects, high-level properties, or is it limited to low-level sensory features?), and the relationship between perception and belief ^[Siegel, S., *The Richness of the Senses*, Oxford UP, 2010].

The *enactivist* tradition, drawing on Merleau-Ponty's phenomenology, challenges representationalism from a different direction: perception, on this view, is not a matter of constructing internal representations but of active engagement with the environment ^[Noë, A., *Action in Perception*, MIT Press, 2004].

The debate between direct and indirect realism remains active and unresolved. What is clear is that perception — however it ultimately works — does not give us a transparent window onto the world; it gives us something whose relationship to the world requires careful philosophical examination.
