Representative/ Indirect Realism

Representative/indirect realists agree that there is a material world that does exist independently of perceivers, but we do not have direct access to this world. We perceive the world indirectly through sense data (sight, smell, taste, touch, sound).

So there are three things involved: the perceiver, sense data and the perceived object.

Indirect realism claims that we see images which represent the real world.

• Sense data are private, no-one else can experience your sense data - so they are subjective.
• Sense data only exist when they are being perceived - so they are temporary.
• Sense data are exactly as they seem. They are appearances and you cannot be wrong about them. You can be wrong about an object being objectively there, but you cannot be wrong about the fact you are having a sense data experience of it. 
• Sense data are immaterial. 

Locke said that there are certain properties 'in' the object (as claimed by direct realism) which do not depend on who is perceiving them. These are primary qualities, these include: shape, size, position, motion and amount.

According to Locke, objects also have secondary qualities, which are dependent on the primary object, and are subjective to the perceiver (they exist within the mind) these include: colour, taste, sound, temperature and smell.

How do we know that sense data really represent the world as it is?

• Representative realism can be accused of making us appear to be trapped in our own private cinema: we perceive the images, and assume this is a true representation of the real world, but the trouble is we can't check whether the representations are true.
• Similarly, it is accused of trapping us behind a 'veil of perception' which we cannot remove to check what the world is really like.

So, do we have any reason to believe that sense data is true to reality? Or that sense data are caused by material objects, and not by Descartes' evil demon or a Matrix?

Locke goes into detail about why he believes the material world must exist as the cause of our perceptions, however each argument has its own problems.

• The material world must exist because if one doesn't have a sense organ for detecting it, one cannot have the perception of the material world.
  - But sense organs themselves are ideas we may be wrong about. 
• The material world must exist because we have no choice about what we perceive. If the perceptions came from our mind, then we could choose what we perceive.
  - But God could be giving us the ideas of objects.
• The material world must exist because there is coherence in the senses.
  - But God could be causing the cohering perceptions.

The indirect realist claims that sense data doesn't block our perception of the real world, sense data are how we see the world. 

• Is it really true that primary are perceiver independent? For example, an object to a child may appear bigger than it does to an adult, or objects may appear doubled when you press the corner of your eye.

• Could we conceive of an object with no secondary qualities? According to indirect realism, the only essential qualities are the primary ones, but we couldn't conceive of an object without any secondary qualities.

• Sense data are immaterial, but if I were to describe a 'square brown sense data' how can it have a shape if it's immaterial?
• Where do sense data exist? Immaterial things can't have a location.
• Do we really need to construct sense data as a seperate thing?