Last week I discussed a thought experiment
by Hume. It says that if we know, for instance, all existing shades of blue but
one, it’s possible to fill in the failing shade in your mind, without seeing
it. This made me think of another thought experiment, which in some way is the
opposite, since it implies that even if we have a full description of all
shades of blue, we still don’t know them. It’s Frank Jackson’s though
experiment about Mary in a black-and-white room. It runs this way:
Mary has
lived here whole life in a black and white room. She has seen everything around
her only in black and white and shadows of grey. In
this way she learns everything there is to know about the physical nature of
the world. She knows all the physical facts about us and our environment, in a
wide sense of “physical” which includes everything in completed physics,
chemistry, and neurophysiology, and all there is to know about the causal and
relational facts consequent upon all this, including of course functional
roles. One day Mary
leaves her room and comes in our world full of colours. But then she learns
something about the physical world she didn’t know before for she has learned what it is like to see something red, say. (see
reference below, p. 291)
On the
basis of this thought experiment Jackson argues that physicalism cannot be
true. Physicalism is the thesis that the actual world is entirely physical. We
can also say that there is nothing over and above the physical and that there
is only one substance in the world: matter. So physicalism opposes Descartes’s
view that there are two substances, namely matter and mind. However, so Jackson,
physicalism cannot be true because
Mary discovers what it is like that a
colour is red when she leaves her room, and just
because this what it is like –
the feeling of redness, I would say – cannot be described in a physical way.
And since Mary cannot know what red
is like by a physical description, physicalism cannot be true (cf. id. pp. 291-2).
All this
seems plausible. If it is true, one conclusion could be that there are (at
least) two substances in this world: matter (the world as described by physics)
and mind (the world as you experience it). I don’t want to say that Jackson
went that far, and I’ll leave it as it is, but my point is that this famous
thought experiment simply is not correct, for it contains a hidden assumption
that includes already its conclusion. According to Jackson, physicalism is the
“challenging thesis” that the actual world is entirely physical and that
accordingly, if this were true, complete knowledge of the actual world is
physical knowledge, as physicalists say (id.
p. 291). However – and that’s my point – the thesis that the actual world is entirely
physical, says only something about how the actual world is; it is on the level of ontology. But the knowledge of the actual world says something about how this world
is described; it is on the level of
epistemology. It’s simply not possible to reduce epistemology to ontology and
it is quite well possible that there are two (or more) unrelated descriptions
of the same object. So even if Mary has learned in her black-and-white
room how the world is in a physical way, we know already beforehand that she
still doesn’t know how the world is in a phenomenal way, for that’s a different
way to describe the world. It’s another type of knowledge. Mary even couldn’t get
this phenomenal knowledge in her black-and-white room and she starts to acquire
it only after she has left her room. By confusing knowledge of the actual world
in physicalist terms with the physical state of the actual world, Jackson
assumed already in his thought experiment what he wanted to prove, namely that
physical knowledge doesn’t lead to phenomenal knowledge. If physicalism isn’t
be true it is for other reasons.
Phenomenal knowledge describes the
phenomenal characteristics of the world like the experienced shades of red,
white and blue. Physical knowledge describes the physical characteristics of
the world like the wave lengths of these shades. This doesn’t suppose, however,
a non-physical mind but only that we can describe
experiences in a non-physical way. And isn’t it so that the mathematical
formulas as used in physics are also mental and that they fit the human mind
just as a phenomenal description of colours does? Be it as it may, it’s not so easy to think out a
convincing thought experiment.
Reference
Frank Jackson “What Mary Didn’t Know”,
See also his “Epiphenomenal Qualia”, https://www.jstor.org/stable/2960077?seq=1#page_scan_tab_contents
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