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

2. 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.

3. 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.

4. 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.

5. 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.

6. 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?

7. 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?

8. 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

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

10. 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