How
can the fine-grained phenomenology of conscious experience arise from neural
processes in the brain? The mystery remains unresolved.  The major difficulty
is that the standard explanations in science and philosophy are cast in
objective terms but consciousness is subjective. Joseph Levine attempts in this
book to defend his rather compelling view that there is an ‘explanatory gap’
(EG for short) between the mental and the physical. According to the EG
theorists, conscious phenomena cannot be explained in terms of physical or
material phenomena. Of course, this idea is not new. John Locke claimed in his Essay,
somewhat 350 years ago, that there is no similitude between the ideas of
secondary qualities and the insensible particles of matter that in different
degrees and modifications of their motions cause these ideas (e.g., ideas of
red or blue color). According to the proto-EGist, it is not impossible to
conceive then that God should annex such ideas to such motions and that he
should also annex the idea of pain to the motion of a piece of steel dividing
our flesh, with which that idea has no resemblance.

Levine’s
view, first discussed in the early eighties (Levine, 1983), holds from a
physicalist viewpoint — in David Chalmers’ jargon type-B materialist that no
physical account can explain conscious experience (one good suggestion is to
read first – if not the Conscious Mind 1996 due to its excessive length
– Chalmers’ "Consciousness and its Place in Nature" in The
Blackwell Guide to Philosophy of Mind, 2003, since Levine draws much on its
terminology and distinctions). He rejects Chalmers’ argument against the thesis
of the supervenience of consciousness upon the physical (conceivability
argument): it is not the case that if it is conceivable that there are zombies
it is metaphysically possible that there be zombies. Therefore, materialism is
not committed to the conceptual impossibility of zombies. According to type-B materialist,
there is an epistemic gap between physical and phenomenal properties but there
is no ontological gap. The mind-body problem remains a problem because we
cannot explain how phenomenal consciousness or the phenomenology of
conscious experience arises from gray matter. How can physical/neurophysiological
processes in the brain give rise to subjective qualitative states? Well, says
Levine, we can’t know because there is an epistemic divide between these two
kinds of phenomena and therefore the problem of consciousness for the
foreseeable future, will remain a mystery.

There
are 6 chapters in the book. Chapter 1 argues for materialism. Levine formulates
his materialism as follows: ‘Only non-mental properties are instantiated in a
basic way; all mental properties are instantiated by being realised by the
instantiation of other, non-mental properties’ (21). One of his main reasons
for physicalism is that it is required if we are to make sense of the causal
efficacy of the mental. There is of course, an alternative – epiphenomenalist
story to tell here (most recently, William Robinson’s Understanding
Phenomenal Consciousness 2004) but according to Levine, ‘the consequences
that flow from epiphenomenalism are very hard to accept and provide sufficient
grounds to avoid it’ (24-25). Both the materialist and the contemporary epiphenomenalist
agree that significant progress has been made on the project of naturalizing
intentionality — one of the main problems of the mind. What they disagree on
is the problem of qualia. On Levine’s account, the essence of qualia is
physical. 

Chapter
2 is almost entirely devoted to defending materialism from the conceivability
argument: Let P be the proposition that everything physical is as it actually
is and Q the proposition that there are qualia. According to Chalmers, (P&
¬ Q) is conceivable and therefore possible. The type-A materialist holds that
(P& ¬ Q) is not conceivable, and Q follows a priori from P. As
opposed to type-A and E-type (see below) materialists, I think that Levine
rightly holds that premises like (i) ‘neural correlate = phenomenal
consciousness’ and (ii) ‘water = H2O’ and are not a priori and therefore zombies
and zombie-H2O are both conceivable. But this alone cannot of
course, show that are possible. Levine draws here a good distinction between
two types of type-B materialists, the E-type and NE-type materialists, the
"exceptionalists" and the "non-exceptionalists",
respectively. The first grant the general semantic framework of a posteriori
necessities but hold that it doesn’t apply to the case of qualia. According to
the E-type materialist, if p is conceivable then it is possible except
from certain propositions about experience that are conceivable due to the
peculiar content of phenomenal concepts but not possible (situations like
zombie-H20 for example, are not conceivable). The NE-type rejects the general
semantic framework. Situations like zombie-H20 are conceivable but not possible. There is however,
no explanatory gap in such situations. Levine’s other reason to reject the
conceivability argument is non-ascriptivism, namely the view that the a
priori is ‘exhausted (almost) by whatever is formally necessary’ (54). Its
implication is that neither (i) nor (ii) can be a priori. If zombie-H2O is
conceptually possible and not metaphysically possible nothing about
metaphysical possibility follows from conceptual possibility (and since there
is nothing special about the nature of qualia, zombies are not metaphysically
possible).

The
main argument of the book is developed in Chapter 3. Interestingly, Levine
rejects the E-type account of the EG, namely that there is an EG because there
isn’t an a priori derivation of qualia from pure physical facts.
According to him, there is nothing unique about consciousness as opposed to
say, water. The reason that the EG emerges is rather that we do not have an
explanation of how physical states realize qualia. This last point is
important. Science explains structure by structure in the causes and whereas
properties like liquidity or solidity can be predicted from the properties of
elementary particles neither consciousness nor qualia can be predicted from the
properties of neurons. It appears that there is no corresponding structure in
consciousness and certainly not in qualia. According to Levine, the fact that
(ii) stands in no need of further explanation as opposed to (i), is because
when it comes to (i) ‘it still seems quite intelligible to wonder how it could
be true, or what explains it, even after the relevant physical and functional
facts are filled in’ (82). And this is why, as opposed to zombie-H2O (‘thinly
conceivable’), situations like zombies are ‘thickly conceivable’. Still,
(P& ¬ Q) is not possible.

But how do
thickly and thinly conceivable situations differ from one another? Levine
explains the difference in Chapters 3 and 6 by claiming that one’s idea of a quale
has ‘substantial content’ that is present to one in a way that his/her idea of
water is not. Our idea of a quale has a determinate and substantial nature and
due to our subjectivity it is accessible to us in an immediate way. This puts
Levine into trouble: First, according to him, the E-type holds that qualia and
phenomenal concepts present us with a special case due to their unique nature
whereas Levine denies that. It does seem, however, that phenomenal concepts
have a special or unique nature according to him, and Levine seems to struggle
in order to hold both that they don’t and that (ii) needs further explanation
as opposed to (i) because somehow they do. Moreover, since (ii) requires no
further explanation after all relevant empirical information is supplied, we
can’t conceive of zombie-H2O after all
empirical information is given. But it is still coherent to conceive of zombies
even ‘after all physical and functional facts are filled in’, and therefore, it
does seem that zombies could be possible. Second, the physicalist has it
(Levine included) that the essence of qualia is physical and Levine needs
certainly to explain more the connection between the physical essence of qualia
and our ideas of them as having substantial content (e.g. how exactly in the
mental-physical case as in the water-H2O
case, both concepts pick out the same situation?).

Chapter 6 argues
against functionalist/eliminativist anti-qualophilic arguments (against the
claim that zombies are conceivable). The conceivability argument upon which
Levine appears to over-depend, is certainly not the only challenge to
physicalism. When he considers the knowledge argument, he grants its epistemic
implications but he doesn’t do much to refute the metaphysical ones — he
merely rejects them for the same reasons that he rejects the conceivability
argument. Of course, the two arguments are quite distinct but in this respect
he agrees with Chalmers in that what we ultimately want to know in both
arguments is whether besides the epistemic gap between the physical and the
phenomenal domains, there is also an ontological gap.

Chapters
4 and 5 argue rather convincingly that the various attempts at explanatory
reduction or elimination, including higher order theories and representationalism,
do not succeed in closing the gap. He states that he is a ‘modest qualophile’
since no materialist theory seems to really explain our experience. The ‘qualia
freak’ (e.g. Frank Jackson 1982) step in deriving a priori that
materialism is false is invalid. Levine’s main reason for physicalism is that
it accounts for the causal efficacy of the mental. How exactly? We don’t know. But
why then not go for a dualist-interactionist picture? Not much is said on this
connection but the problem is well-known and the difference is rather
terminological: If something is causally efficacious then it must be physical. 
Purple Haze is a thought provoking, well-written and honest book.
Levine’s position is one of the few positions that confront these problems
without trying to explain them away or denying any of the phenomena. The book
is fairly technical at places and aimed primarily at a philosophical audience
but I would recommend it to anyone who is interested in the problem of
consciousness and especially in the issues involving conceivability and
possibility.

© 2005 Dimitris Platchias

Dimitris
Platchias is studying for a Ph.D. in philosophy in the University of Glasgow.  His
main interests lie in the Philosophy of Mind and especially in the Philosophy
of Perception and Consciousness.

Categories: Philosophical