What do we know – continued – what are you looking at?

Sense data fills the gaps between our eyes and the world around us.  But is it a straw man in the argument for experience?  By Lisa McLellan

My last article introduced you to Descartes and his famous statement ‘I think therefore I am’.  Descartes rejected all beliefs that he considered even remotely doubtable in order to arrive at a foundation of absolute certainty.  One of the first categories of beliefs to be rejected was beliefs based on sensory information.

Descartes recognised that a particular experience, e.g. the experience of seeing an apple, is no guarantee that an apple is actually there.  The experience may be an illusion, and in fact there is a nectarine that looks particularly apple-like.  Maybe the experience is a hallucination and there is in fact nothing there at all.

This week I am going to talk about a thing called sense data.  Sense data were posited in response to the problems discussed above.  If sense data exists, Descartes would no longer have to worry about the unreliability of sensory experience.  He could at least say, with certainty, that he is experiencing a round, red, apple-like sense datum, without making any commitment to the existence of an apple, a nectarine, or anything at all.

So what are sense data?

Sense data are thought to be the direct objects of our experience.  They are what we become directly aware of when having a sensory experience.

In the example of the apple, the sense datum remains the same whether the object in front of me is an apple, a nectarine or nothing at all – because the thing we are seeing, not the object causing it, is the sense datum.

In this way, sense data can account for the similarities between veridical perception (in which our experience is accurate) illusion (in which our experience corresponds to an actual object but misrepresents it) and hallucination (in which our experience does not correspond to any actual object at all).

Why bother?

So why suggest that there must be some immediate object of awareness?  The common sense view of perception is simply that we can be directly and immediately aware of the physical objects that we see around us.

Supporters of the sense data theory argue that this cannot be the case.  They argue that what I am directly aware of when I look at an apple cannot be the apple itself.  If I change my position in relation to the apple, or change the lighting in the room, then the picture I see changes.  The apple does not change.  Therefore the sense data theorists argue that what I am directly aware of cannot be identical with the apple itself.

This argument rests on the assumption that there is something (not the apple) of which I am directly aware, and this something is what changes when I move or change the lighting.  But do we need to admit that there is something that changes?  In positing such an entity, a sense datum, we contradict Occam’s razor.

Keep it simple, stupid!

Occam’s razor is a logical principle which states that we should not multiply entities beyond necessity.  In other words, if we don’t need to posit sense data in order to explain perception, we should avoid doing so.  By introducing sense data, we complicate things by introducing more concepts than are necessary.

In order to take this line of argument, one would be required to demonstrate that sense data are not in fact necessary for us to explain perception.  It is out with the scope of this article to attempt such an explanation, so I will have to leave you with my unsupported assurance that such an explanation is possible.

I do not believe that an experience must be an experience of something (i.e. a sense datum).  In the case of hallucination and illusion, we have an experience as if an apple were before us, and this does not mean that there exists something apple-like (a sense datum) which we are experiencing.  I also believe that sensory information is much more reliable than it is given credit for.  However, I shall leave that argument for another day…

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