black-and-white room. At the point where he takes up the story, Mary has
never had any experience of colour; but, we may suppose, there is nothing
wrong with her visual system – she still has thecapacityfor colour vision.
Now, Mary is also a scientist, living in an era much more scientiWcally
advanced than ours. So Mary may be supposed to knowall there is to know
about the physics, physiology and functional organisation of colour vi-
sion. She knows exactly what takes place in someone’s brain when they
experience red, for example, and has full understanding of the behaviour
of the physical systems involved. So she knows all the objective, scientiWc
facts about colour vision. But there is one thing she doesnotknow, surely,
and that is what an experience of redis like. And on being released from
her black-and-white room there is something new she willlearnwhen she
experiences red for theWrst time. Since knowledge of all the physical and
functional facts does not give Mary knowledge ofallthe facts, Jackson
argues, then there are some facts – namely, facts about subjective experien-
ces and feelings – which are not physical or functional facts, and which
cannot be explicable in terms of physical or functional facts, either.
One inXuential reply to this argument is developed at length by Lewis
(1988). It turns on a distinction between two diVerent kinds of knowledge.
On the one hand there ispropositionalknowledge (often called ‘knowledge
that’), which is knowledge of facts; and on the other hand there ispractical
knowledge (often called ‘knowledgehow’), which is knowledge of how to
do something. Thus your knowledge of British history is propositional
(you knowthatthe Battle of Hastings was fought in 1066, for example),
whereas your knowledge of shoe-lace-tying is (largely) practical – there are
very fewfactswhich you know about tying your shoe-laces, and you would
be at a loss totellme how to do it (except by running a description of what
to do oVa memory-image of the appropriate sequence of actions); rather
you justcando it; you have the ability to do it. With this distinction in
place, the reply to Jackson can be that knowing what an experience is like
is not propositional knowledge, but rather practical knowledge.
What Mary lacks in her black-and-white room, on this account, is an
ability– the ability to recognise, remember and imagine experiences of red.
And what experience teaches her, on her release from the room, is just that
- an ability to recognise experiences of red (without having to rely on any
inference from physiological facts), and abilities to recall and visualise
such experiences. So there need be nofactsover and above the physical and
functional facts which Mary already knew. For she does notlearnany new
facts when she comes out of her room. Rather, she acquires some new skills
which she did not have before. And this need cause us no problem. For no
one would want to maintain that mere knowledge of facts can confer
practical abilities on someone – knowledge of all the facts about skiing
would not make you into a skier, for example.
236 Consciousness: theWnal frontier?