To: Diane F.
From: Geoffrey Klempner
Subject: Perception and the limits of human knowledge
Date: 6th June 2008 12:55

Dear Diane,

Thank you for your email of 26 May, with your fourth essay for Possible World Machine, in response to the question, 'What is perception? Explain the role of perception in an account of the nature and limits of human knowledge.'

I did not know that 'cats do not go around'. That's very interesting! I want to start with this because it shows something about the nature of perception which tends to get left out when we concentrate on 'perceiving a table' or 'perceiving a tomato'.

Cats are great at jumping and scampering up steep inclines so it is hardly surprising if a cat's first instinct is to climb over rather than go around. However, human beings faced with a similar choice do not depend on instinct but rather on our *perception* of the obstacle, in its context.

Just as you can perceive an object, conceived as an obstacle, so you can also 'perceive' a possible route past the obstacle. A car driver sees 'room to squeeze through' and makes for the gap in the traffic.

Scepticism about perception seems absurd, or pointless, when seen in this practical context. Could one go further and state that the very nature of the 'things' which we perceive is defined by our practical interests? That's a point that one of the speakers makes in the unit on perception.

Seeing something *as* a possibility of going through, or over, or round is just one dimension, where we are concerned with the action of getting from A to B. But there are many other kinds of action which involve other kinds of corresponding perception. Say that I am a bit overweight, and I cast a glance at the collapsible chair offered by my host, trying to gauge whether it will bear my weight. Or, I gently pick up the tiny glass figurine from the mantelpiece, because I see it *as* fragile.

What this more generalized notion of perception implies is a capacity for judgement which is in a sense unmediated by calculation or reasoning. I can see just by looking at your face that you are worried (perception) or I can work it out from various bits of evidence that I have pieced together, such as actions you have done or emails you have sent. The end judgement -- the fact that you are worried -- is exactly the same in both cases but the route taken to get there is very different. This shows something essential about the concept of 'perception'. To say that perception is essential to human knowledge is to assert, as a necessary or a priori truth, that *not* all knowledge can be acquired by 'calculation or reasoning'.

Understanding another person's words is another important example of perception. There is all the difference in the world between hearing someone 'say' something, and struggling to translate someone's words using a dictionary or phrase book.

The question is about the 'nature and limits of human knowledge'. Why is perception needed for knowledge? Could there be beings who didn't need powers of perception? 'Only if they already had all the knowledge that they would ever need.' However, that seemingly obvious response doesn't answer the question. Computers don't perceive, but they do have informational inputs (CD drives, keyboards etc.). Each of us has lots of knowledge which can be expressed verbally -- in a way that could be uploaded into a computer -- but there has to be some other way of acquiring knowledge, which is prior to verbal expression, otherwise there would be nothing for the words to be 'about'.

You give the well known example of wondering whether the colour we call 'blue' is the same for both of us. A blind person knows what 'the sky' is, in a sense, they can talk intelligently about the sky (as something aeroplanes fly across, has occasional clouds, as a place where you could keep going 'up' forever and so on) so what exactly is lacking in their knowledge? What does a knowledgeable blind person *not* know about the sky?

Let's start taking away the senses. Sight, sound, smell. Touch? could you take away that too? Helen Keller was deaf and blind, but her teacher still had the rich resources of feeling and touch to call upon. You can see where this is going. Imagine a human being with even more impoverished senses, who is only capable of feeling one thing, a sharp pin prick, or a whiff of onion. Would you try to tap out a Morse code of pin pricks or onion whiffs? How could they possibly learn how to decipher the code?

And yet, someone whose senses had decayed over time might reach precisely this state, not losing their knowledge, still able to communicate.

These questions are very difficult. Of course, one can discuss all the usual things about perception such as arguments for or against idealism, qualia and so on. But, to me, the issue of the 'nature and limits' of human knowledge is looking for something more fundamental, something which in a sense we need to tackle first, before we get into all these fangled philosophical issues.

All the best,

Geoffrey