David asked:

To what extent does our internal reality affect our perception of the external one?

Who do I read to argue that our perceptions of the world bear any relation to actuality at all?

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The British empiricist John Locke deals with perception in some detail and inspired a lot of literature
on the subject. Locke thought that our perceptions of the world bear relation to actuality. He holds that
we perceive things if and only if we have mental ideas of them. An idea is an object with properties —
colour, shape etc. — of its own and can mean a perception, a sensation or a thought (Locke is
careless with his terminology). We see our perceptual 'sensory' ideas as possessing various visible
properties (e.g. I see my coffee mug as yellow and mug-shaped) These visible properties I see
'resemble' those of the external object itself and which I see by means of ideas. This is my 'internal
reality' on Locke's grounds.

This position is known as indirect realism and is open to several objections: the first surrounds the
idea that we must see a mental image in order to see a physical object. By the same token, it seems
that one would need another visual image to see the first image (if ideas have the same ontological
status as objects — as 'pictures in the head'). Therefore we have an infinite regress. A possible 'fix' to
this objection is that it would be like saying that we can use infa-red to see in the dark; we don't need
a second set of infa-red images in order to see the first set of infra red images.

A more fundamental problem is that external objects, the indirect realist must claim, can only be seen
indirectly, through a 'veil of ideas'; how do we know that our perceptions of our ideas do bear relation
to the world? We are subject to illusion over external objects but never about ideas.

The thought here is that representation of the world is achieved by the fact that there is a
resemblance between the properties we perceive in our ideas and the properties of external objects.
This fails to answer the question of what it means to perceive an object.

You can hold a resemblance theory without being committed to the view that ideas are objects
however by denying the incoherence of cross-category predication: 'ideas' and 'objects' cannot share
properties.

Some predicates, namely logico-mathematical ones, are structuraldescriptions, the point being that
structures from different domains can be isomorphic.

For example:

*We use the structure 1, 2, 3, n to represent days of the month.

*There is a structural isomorphism between the combination of zeros and ones on a CD, the sound
when it is played, and the musical patterns of notation (cf. Wittgenstein Tractatus4.04).

It is at least a coherent claim that there is a structural isomorphism between the properties we
perceive by means of ideas and properties of objects themselves. The best qualities to use as
candidates for resemblance with our sensory ideas are geometric ones, properties involving
description in terms of logic and mathematics and which correspond to what Locke calls 'primary
qualities'.

Kant has a different approach; roughly, raw intuitions (which correspond to sensory impressions in
Locke) must be given to us through the mode of space and time. Space and time are a prioriin that
we bring them to experience from within rather than grasping them from without. This is because
space and time are presupposed in there being any experience at all.

Empiricists assume all concepts are derived from or are reducible to sensory intuitions. There can be
no concept without a corresponding sensory stimulus — the meaning of concepts is given in terms of
this synthesis. Kant argues that this is a confusion of experiences and sensations. Experience
provides the grounds for the application of concepts because it already contains concepts. Sensation
or intuition contains no such concept. All sensation is without structure until transformed by mental
activity. Therefore sensation provides no grounds for belief. If we understand our experiences, this is
because they already contain concepts which we supposedly derive from them. These concepts
come from the structure of understanding itself. Thus there are also concepts not given in experience
because they are presupposed in it. They are involved in every apprehension of the world; not to
have them is not to have experience but mere intuition, from which no knowledge can be derived.

Kant calls these fundamental concepts 'categories'. Substance is one such category — it is that which
is able to exist independently and which supports the properties which depend on it and which we
see. 'Coffee mug' is a specification of the a prioriconcept 'substance' and can only be grasped when
you have grasped the a priorinature of substance. Causality is another category which we bring to
our perceptions. Any knowledge at all must come from the application of the categories to our
intuitions.

Adam Gatward

You could read John Locke, and Rene Descartes to get two very different views concerning the
relation between our perceptions and reality. In recent philosophy read The Problems of Philosophy
by Bertrand Russell, and Sense and Sensibiliaby J. L. Austin.

It seems clear that the data we receive from "external reality" is filtered through our mental apparatus
and our sense faculties, like our eyes and ears. Our ability to see colors, for instance, depends on the
fact that our eyes have rods and cones. Dogs, who do not, are color blind.

There is a lot of dispute as to what extent what we receive from our senses matches reality. But
consider this: physicists tell us that the world is really made up of unobservables, electrons, neutrons,
and so on. In that case, although there is an external material world, it is nothing like what it appears
to us in "commonsense." This view is sometimes called "scientific realism."

Kenneth Stern