Michael Lacewing enquiries@alevelphilosophy.co.uk Sense data Michael Lacewing enquiries@alevelphilosophy.co.uk © Michael Lacewing

How do we know about the physical world? We perceive physical objects, which exist independently of our minds. But do we perceive them ‘directly’ or via some form of mental representation? What we perceive isn’t what exists independent of the mind.

Illusions In illusions, you see something, but not as it really is. What you see is an appearance. In veridical perception, you still see an appearance immediately, and the object via its appearance.

Appearance and reality What we see are ‘appearances’, which are mental things What is bent if it is not the stick? What I see in a hallucination We discover physical reality through how it appears to us in sense experience.

Sense data Private: part of an individual consciousness Physical objects are public Mind-dependent: only exist while being experienced Physical objects exist without being experienced They are exactly as they appear. Physical objects can appear differently from how they are.

Objections How do we know reality is anything like our experience? We can’t compare sense data with physical objects Worse: sense data can’t have, e.g., size and shape the way physical objects do But then – how can the sense data of the bent stick be bent?

Objections Can sense data have properties I am not aware of? Number of matches How do we know there is a physical world, causing our sense data?

Implications Can sensory experience give us knowledge of (rather than just beliefs about) the physical world? Hume accepts a form of scepticism: We can’t prove the existence of the physical world, but belief in it is irresistible Experience gives us all we need practically

Implications Empiricist alternatives: a different analysis of experience Reject sense data (direct realism) or Rejects the existence of physical objects (idealism)

Implications Rationalist alternatives: Plato: there is only belief concerning physical objects; knowledge is of the Forms Descartes: we must prove the existence and essential nature of physical objects using reason