• The existence of physical things seems obvious to non-philosophers but raises significant philosophical difficulties, with no generally accepted proof of ordinary physical objects’ existence, comparable to the proof of God’s existence.

• Common belief is immediate awareness of physical objects, often justified by saying: “We see them.”

• Most philosophers argue we are not immediately aware of physical objects; strong arguments support this view.

• (1) Empirical evidence shows perception depends partly on our sense-organs—we cannot see without eyes, and altered sensory organs cause illusions (e.g., optic nerve damage causing false images).

• Unusual conditions (blows to the head, drunkenness, jaundice) alter perceptions, indicating that what we perceive depends on our perceiving apparatus, not just external objects.

• Objects we perceive depend for their existence on our perceiving them, though external physical things causally influence our perceptions.

• (2) We presumably perceive things as they are, but illusions show we often do not perceive physical objects as they truly are.

• Different observers can see the same object differently (e.g., differing shapes), which cannot be literally true—thus, they are not perceiving the same thing.

• These arguments support the representative theory of perception, which states that what we immediately perceive is not the physical object itself but an image or representation created in the mind by the object acting through the sense-organs.

• This representation has been called a representation, idea, sense-datum, or sensum.

• The theory is paradoxical but hard to refute given the supporting arguments.

• If sense-data are taken as elements purely from sensation, it is doubtful we ever perceive pure sense-data alone.

• Immediate consciousness is likely mingled with memory and interpretation, not just the direct result of objects acting on sense-organs at the moment.

• The representative theory’s point is that the immediate object perceived is not just sensation but is not identical to any physical object conceived realistically, nor does it exist independently of perception.

• Whether this immediate object is given by sensation alone concerns its causation, not its nature.

THEORIES OF PERCEPTION

• If we reject the representative theory for some perceptions, only three difficult alternatives remain.

• The first alternative is to deny the existence of physical things independent of human perception; in this case, there is nothing for ideas or sensa to represent.

• This first alternative will be discussed later but challenges the notion of an external physical reality.

• The second alternative asserts that everything we perceive exists in the physical world exactly as perceived.

• This view struggles to reconcile the existence of incompatible perceptions (e.g., two different colors occupying the same space simultaneously), which is self-contradictory.

• If all perceptions existed independently and exactly as perceived, conflicting qualities would have to overlap in physical space, which is impossible.

• This theory fails to explain perceptions of change (e.g., an object appearing to change shape or size as we move), which would be illusory since all shapes and sizes would exist simultaneously.

• Admitting illusions undermines the theory’s goal to hold that we always directly perceive physical objects, making such paradoxical claims hardly worthwhile.

• The third alternative holds that we always perceive physical things directly but are mistaken in our perceptions.

• This seems less paradoxical but leads to the radical view that immediate experience itself is mistaken, unlike the other views which see error in beliefs about experience.

• Example: a stick partly in water appears bent.

  • According to the representative theory, the bent object seen is a mental representation or sensum, and immediate experience is trusted.

  • According to the third alternative, nothing is bent physically; the stick is straight but appears bent—an error in perception.

• However, since we clearly see something bent, something bent must exist as an image in the mind; without it, the bent appearance could not be seen.

• Immediate experience must be accepted as reliable, as all empirical evidence depends on it.

• The error of perceiving something bent when nothing bent exists cannot be explained by a superficial analysis of experience because the bent appearance persists no matter how long we observe.

• Almost all immediate experiences involve an element of illusion, for example due to changing spatial position.

• Most philosophers hold we cannot be mistaken about qualities we immediately experience, but even if mistaken, admitting widespread error leads to radical scepticism.

• If immediate experience is not trustworthy, it is unclear what else could be.

• Therefore, it seems almost necessary to adopt the representative theory for at least some perceptions.

• A partial representative view, accepted by common sense, holds that ordinary physical objects are perceived directly, but things like rainbows, mirror images, or hallucinations are mere appearances.

• Few philosophers have accepted this compromise fully.

• The main objection is that almost all perceptions contain some element of illusion, influenced by spatial position or sensory structure (e.g., objects look different under a microscope versus the naked eye).