The problem of subjectivity, also called the "explanatory gap" or the "hard problem" (cf. Bieri,
1992, Chalmers, 1996, Jackson, 1982, Levine, 1983, and Nagel, 1974, 1980), is based on the
dichotomy between the - in some sense - irreducible subjective character of our phenomenal
experience (qualia) and the quasi-objectivistic explanations of science or any third-person
description. We will never know "what it is like to be a bat" (or even my own twin brother) even if we
could know everything physical including all NCC in every detail. But this is not necessarily an
ontological problem and therefore a dread for naturalism (taken as an ontology). The difference
between the first- and the third-person perspectivity might be just a result of the different modes of
presentation and the different concepts which we apply, hence it could be seen as an epistemic
and conceptual difference, but not an ontological one (cf. Tye, 1995).
The problem of other minds is obviously insurmountable: I cannot inspect the mind of other
individuals, because I cannot log in their brains or minds or be part of them. I can only interpret their
behavioral and maybe physiological actions and responses (including verbal reports). If they are
zombies without inner experiences I would never know. If they are perfect actors or liars with quite
different experiences I could not know either. Maybe I could detect contradictory physiological
states, but to interpret them as contradictory, I still have to compare them with some standard and
need an argument why this very case is not just an exception to the rule.
Furthermore, maybe it is even self-deceiving to attribute something like "inner experiences" to
others. Maybe this is just an advantageous "intentional stance" to cope with their complex behavior
or some sort of a linguistic illusion or a social construct (cf. Blackmore, 1999). Maybe it is self-
deceptive to attribute "inner experiences" to myself, too. Studies of human development (which are
admittedly controversial) give at least some hints that knowledge of one's own mental states is -
contrary to common sense - not immediately given but as indirect as the knowledge of other
minds: the infant has to learn at first by inference from its own behavior and the behavior of others
in which mental state it is (Gopnik, 1993). Furthermore, there is reason to believe that we are
systems which permanently confuse themselves with their own self-model, as Thomas Metzinger
(1993) has put it. In doing this, we generate an ego-illusion, which is stable, coherent, and cannot
be transcended subjectively, i.e. on the level of conscious experience itself.
But I do not want to propose that consciousness is something which is nothing at all. For in this
case we need not look out for NCC. Nevertheless, as the discussion about the temporal structure
of conscious events has shown, there is reason to believe that our mental states are not always
transparent to ourself. How could we know if the correlations between neural and conscious events
we observe are not biased in a systematic, misguiding way? This is, for example, one of the main
problems of Libet's interpretation of the temporal order: it is very difficult to prove that the person's
clock-reading and self-reports are really reliable.
II.3. "Leave Mine To Me" - Variations And Complexity
Another limitation of the detection of NCC are interindividual differences in neural structure and
dynamics and intraindividual variations in the course of time. Not even identical twins have identical
brains. Individual variations are one of the most important restrictions of a generalization of
functional brain-imaging techniques. Furthermore, they undermine a fine-grained lawful one-to-one
correspondence between neural and mental states: If it is possible at all that two persons are
exactly in the same mental state at a given moment, this mental state obviously cannot depend on
an exactly identical neural state even if we could neglect the environment (which of course we
cannot, cf. II.4.). Thus, conscious states are realizable in different ways (cf. II.5.).
Interindividual differences could be enormous in cases of developmental impairments and plastic
reactions after that. For instance, there are quite normal people who are missing big parts of their
brain due to early childhood surgery. And in the case of hydrocephalus, an increase in the volume of
the cerebrospinal fluid could stretch the cortex into a sheet of tissue only a few millimetres thick
without damaging it and without impairing intelligence. In a computer tomography scan, the head of
a hydrocephalus appears largely brainless.
Investigating the brain on the cellular and subcellular level, it is nearly impossible to get detailed
maps of the neural networks and their activities and to handle their complexity. This is a major
obstacle for the discovery of sufficiently precise NCC. Furthermore, it is an open question, which
kind of reduction is possible (Vaas, 1995a), and which levels of description, abstraction and
generalization are most useful for philosophical purposes.