Can minds do more than brains? Is this a scientific question? Scientists
and philosophers today generally assume that minds and brains are equivalent,
that there is a one-to-one correspondence between the mental states and physical
states of one's brain. A recognised scientific term for this assumption is
"psychophysical parallelism," which both
Kurt Gödel and
Ludwig Wittgenstein regarded as a prejudice
of our time. Of course, a prejudice is not necessarily false. Rather, it
is a strongly held belief which is not warranted by the available evidence,
the intensity of the conviction being disproportionate to the evidence for
Locating the site of mental activities is not obvious from everyday experience.
For instance, the same Chinese character hsin or xin, often translated mind-heart
or body-mind, stands for both the mind and the heart, suggesting that mental
activities take place in the organ of the heart. The Greek philosopher Empedocles
also thought that the mind is located in the heart, taken as the material
organ. Of course, nowadays we are aware of the existence of empirical
evidence indicating that the brain is directly associated with one's mental
activities. For example, if some parts of the brain are damaged or removed
or somehow disconnected, certain mental activities cease.
But the available evidence is far from proving that every mental state
corresponds to a unique physical state in the brain. For all we know, certain
subtle changes in the mind may correspond to no physical changes in the brain.
That is why psychophysical parallelism is, relative to our present knowledge,
only an assumption. We seem able to observe more mental differences than
physical differences in the brain. For instance, if we think of the spectacular
mental feats of Franz Schubert or
Albert Einstein, we are far from being in
a position to discern enough physical differences between their brains and
some physically similar brains to give an adequate account of the drastic
difference in their respective outputs.
Even in ordinary experience, it is difficult to exclude the possibility that our minds make more distinctions than our brains. For example, I have tried to reconstruct my discussions with Gödel in the 1970s with the help of certain rough notes that I made at the time. These notes reminded me of many things. Presumably, my brain contains certain physically discernible traces which are not represented in actual notes. But it is also possible that my mind remembers more than is embodied in these traces in the brain.
Wittgenstein suggested a thought experiment which seems to give a more precise formulation for such a possibility. He imagined someone making jottings, as a text is being recited, that are necessary and sufficient for that person to reproduce the text. He continued: "What I called jottings would not be a rendering of the text, not so to speak a translation with another symbolism. The text would not be stored up in the jottings. And why should it be stored up in our nervous system?" In other words, certain reminders stored on paper are, as we know, often sufficient to bring about a correct reproduction. For all we know, this may also be the case with the brain: namely, that it may contain just sufficient reminders rather than counterparts of everything in the mind.
One reason for the belief in psychophysical parallelism is undoubtedly an
inductive generalisation from the great success of physics-not only in dealing
with physical phenomena, but also in dealing with biological issues, notably
on the molecular level. Indeed, as science advances, we tend to detect closer
and closer correlation between mental and neural events. Yet, given our
experience with the striking distinction between the physical and the mental,
it is by no means clear that, of the comprehensive assertion of parallelism,
how typical a part our limited knowledge of correlation makes up. At the
same time, we are struck by the contrast between the maturity of our study
of the physical world and the primitive state of our attempts to deal directly
with mental phenomena. There is a natural inclination to equate "science"
with the science of the physical world. Consequently, one is inclined to
believe that, if mind cannot be explained in terms of the science of the
physical world, then it cannot be explained in any scientific terms at all.
Given such a belief, psychophysical parallelism becomes a necessary condition
for the possibility of a scientific treatment of mental phenomena.
Even though we have so far failed to study mental phenomena nearly as systematically as physical phenomena, this fact in itself is not proof that parallelism is true, or even irrefutable. We do not know whether or not we will be able to study mental phenomena directly in an effective manner.
In our discussions in 1972, Gödel conjectured that parallelism is false, and that it will be disproved scientifically- perhaps by the fact that there aren't enough nerve cells to perform the observable operations of the mind. In this context, observable operations undoubtedly include the operations of one's memory, reflection, imagination, etc., which are directly observable only by introspection. As we know, what is observable by introspection can often be communicated to others in such a way that they can also test the observations with the help of analogous introspective observations. There is no reason why introspective evidence should be excluded altogether.
The conjecture about there being not enough nerve cells to perform the
observable mental operations illustrates significantly a test of what we
mean by a problem being "scientific." Certainly, the capacity of nerve
cells is a natural and central topic of study for neuroscience. At the same
time, the observable operations of the mind are also things which we are
capable of knowing. These facts are undoubtedly the reason why our initial
response is to agree with Gödel that the conjecture is indeed a scientific
one, even though many people would guess that the conjectured conclusion
is false rather than true.
What is attractive about the conjecture is the apparent sharpness of its quantitative flavour. But the number of neurones in a brain is estimated at 1011 or 1012, and there are many more synapses than neurones. We are not accustomed to dealing with the implications of such large numbers of units, and our knowledge of their actual capacities-in particular, of the expected gap between their combinationally possible and their actually realisable configurations-is very limited indeed. Moreover, as we know, the mind increases its power by tools such as pencil, paper, computers, etc., by learning from others; and by using books and one's own writings as a kind of external memory.
We have little knowledge of the extent to which the brain does the same sort
of thing, too. Therefore, the situation with the brain may be less clear
than Gödel seems to think. At the same time, we are at present far from
possessing any sort of fully promising idea to guide us into the quantitative
determination of all the observable operations of the mind. Even though we
are at present far from being able to decide whether Gödel's conjecture
is true or false, it is hard to deny that it is a meaningful-and scientific
conjecture. Indeed, the conjecture seems to me to illustrate the possibility
of a definitive resolution of the perennial controversy between materialism
and idealism, which has been considered so important in so many different
HAO WANG, logician, has been professor of logic at The Rockefeller University in New York for nearly three decades. From 1961 to 1967, he was Gordon McKay Professor of Mathematical Logic and Applied Mathematics at Harvard University, and from 1955 to 1961, John Locke Lecturer in Philosophy, then reader in the philosophy of mathematics, at the University of Oxford. He is the author of many articles and several books on logic, computers, and philosophy including From Mathematics to Philosophy; Beyond Analytic Philosophy; Reflections on Kurt Gödel and Computation, Logic, Philosophy.
How Things Are: A Science Toolkit for the Mind