Marianne asked:

Do blind people dream of objects and colours? if so does that mean there would be evidence of a
priori knowledge? and if that's so does that then point towards the possibility of the soul/spirit being
separate? and if all this is so would there be a possibility of our awakening state being actually a
dream, and our dreams being real? although there could be the possibility of maybe both being in
some way real, as we only know what a small portion of our brains actually do? Please reply as this is
a question my tutor wouldn't attempt to answer.

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It depends on why they're blind. You experience colors, shapes, etc., because parts of your cortex
are (1) processing "information" (a loaded term, since it comes from computers) from visual inputs in
the eyes (2) because outputs from those areas in the cortex are then integrated into whatever system
(prefrontal/reticular, probably) involves consciousness. So you can be blind because (1) there's no
incoming visual information; (2) the cortex isn't working, (3) cortical processing doesn't get inputted
into the "consciousness modules", or some combination of those.

If you've got eye injuries, so you're blind for (1) only, then you can indeed dream in colors, shapes,
etc... assumingthat the eye injury didn't take place tooearly, in which case you probably also have
problems with (2), because early input is necessary for cortical development. Hey, I didn't claim this
would be an easy answer, did I?

There are, I think, extremely rare instances of (3) being the case, where people have been in an
accident and lost consciousness of all or some part of vision without losing processing. See
"blindsight", also see the Sachs write-up of the painter who had a concussion and lost color vision
(and nothing else - he still had black and white - but he also forgotcolors).

Now, I do not think that any of the above is relevant to the issue of a priori knowledge. It is clearly the
case, for people blinded because of brain injury to the appropriate areas of the cortex, that they
completely lose sight, including dreaming in colors, and so forth; yet of course they remember that
they once saw. This is an interesting example of a memory being ofsomething without beingthat
something, isn't it, whereas usually when we remember, we also "bring up", to some extent, the
original stimulus. It is also the case, for the rare person born with such brain damage and no other
damage (so they survive, are able to speak, etc.), that they have no knowledge at all, except by
inference from other people, of what seeing is like. Think about the difficulty of explaining colors to a
color-blind person, or sounds to a person born deaf.

There is a huge amount of literature, in the areas of neurophysiology, vision, and cognitive science, to
name only a few, dealing with this and related questions, which many many people are very
interested in and actively investigating. You might look at Stephen Palmer's work; he's an expert in
vision and cognition. But you need some background in biology to follow this literature. This is a case
where, unfortunately, people with little background in the field cannot just plunge in.

Steven Ravett Brown

Your tutor probably didn't have time to answer this question!

You must be thinking of "one born blind", as Berkeley says, since if a person has experienced sight
there is no reason why he would not dream of objects and colours. Ideally, we should ask "one born
blind" and I wish I knew such a person now that you have raised the question!

Berkeley would say that without sight there could be no dreaming of colours and objects and I think
most philosophers — and non-philosophers — would agree.

You cannot have a priori experience of empirical states of affairs. A priori knowledge is acquired
non-empirically, i.e. not from the world, but within the mind, or rationally. If a person who was born
blind did dream of colours and objects it would be because he moved in a world with such things —
but this does not make the knowledge a priori. There are cases of "blind sight" — and I'm afraid I
cannot remember the sources of these cases, but they probably come from psychological
experiments — in which a person can detect what is before him. While this person is blind (not
necessarily born so) he can identify a triangle, as opposed to a square with no phenomenological
experience. That is, there is no sense experience, no "look" that the person experiences, but he
identifies and so perceives a shape. Somehow the object to mind relation bypasses
sense-experience, but this is still empirical knowledge. If this can be so, then such a person may well
dream in a way we, who have not any idea of what blind sight is like, cannot imagine. I don't think that
there are "blind sight" cases of colour. However, if this is true for shape there is no reason that such a
person cannot dream of shapes. Components of dreams are based upon sense-experience, but there
may be some sort of experience involved in blind sight. That perception without phenomenology is
some sort of experience is evidenced by our wondering what it can be like.

There is no essential connection between a priori knowledge and the soul. Even rational thought
involves the use of concepts acquired from the real world. It might be thought that this is not true for
mathematics and logic, for instance, but Wittgenstein has argued that we cannot follow rules alone.

It wouldn't follow specifically from the separateness of souls that we couldn't tell dreams from reality.
This is a possibility which is considered in relation to embodied existence: This is the problem of
scepticism. If you haven't encountered this yet, you will.

Rachel Browne