Describing this structure is an
interdisciplinary task I commend to philosophers. My aim for now is not to do it
-- that's a long term project -- but to describe the task. This requires
combined efforts from several disciplines including, besides philosophy:
psychology, linguistics, artificial intelligence, ethology and social
there is not just one sort of mind. Besides obvious individual
differences between adults there are differences between adults,
children of various ages and infants. There are cross-cultural
differences. There are also differences between humans, chimpanzees,
dogs, mice and other animals. And there are differences between all
those and machines. Machines too are not all alike, even when made on
the same production line, for identical computers can have very
different characteristics if fed different programs. Besides all
these existing animals and artefacts, we can also talk about
theoretically possible systems.
A common approach to this space of possible 'behaving systems', to coin
a neutral phase, is to seek a single sharp division, between those
with minds, consciousness, souls, thoughts, or whatever, and those
without. Where to draw the line then becomes a major problem, with
protagonists of the uniqueness of man, or of living things, or
champions of machine mentality, all disputing the location of the
boundary, all offering different criteria for allocating things to
one side or the other.
passion accompanying such debates suggests that more than a search
for truth motivates the disputants. To a dispassionate observer such
debates can seem sterile.
sides assume that there is some well-defined concept of 'mind',
'consciousness', or whatever, whose boundaries are to be discovered,
not created. But these are complex and subtle concepts of ordinary
language, not designed for scientific classificatory precision. When
using them of our fellow men, or animals, we don't first check that
certain defining conditions for having a mind or being conscious are
satisfied. Rather we take it for granted that concepts are
applicable, and then we make distinctions between quick and slow
minds, conscious and unconscious states, feeling of various sorts,
etc. Equally we take it for granted (most of the time) that such
concepts and distinctions cannot be applied to trees, lakes, stones,
clouds. (However, not all cultures agree on this.) But we don't
discriminate on the basis of any precise shared definition of the
essence of mind,
consciousness, or whatever. For there is no such precise shared
traditional way to seek an essence is through introspection. However,
nothing learnt in this way about the nature of mind or consciousness
could help us distinguish other beings with and without
approach is to seek behavioural definitions of mental concepts: but
these founder on the objection that behaviour merely provides
evidence or symptoms and does not constitute what are
essentially internal states.
only alternative until recently has appeared to be to locate mind in
brain matter - but this ignores important category distinctions:
although neuronal states, events or processes may correlate with my
being conscious, they are not themselves consciousness. Consciousness
is not anything material.
any other attempt to identify a referent for 'mind', 'consciousness',
'pain' etc. has, until recently, looked like an attempt to populate
the world with mysterious, inaccessible metaphysically unjustified
is different now is that Computing Science has provided us with the
concept of a virtual machine, within which computational
states and processes can occur. A virtual machine has much in common
with the kind of formal system studied by mathematicians or
logicians. It is an abstract structure which can undergo various
changes of state. A virtual machine can be embodied in a physical
machine without being that machine. The same virtual machine
can be embodied in different physical machines. Different virtual
machines can be embodied in the same physical machine. Different
virtual machines can have very different abilities. Work in
Artificial Intelligence has shown that some virtual machines can
produce behaviour which previously had been associated only with
minds of living things, such as producing or understanding language,
solving problems, making and executing plans, learning new
strategies, playing games. By studying the space of possible virtual
machines we can replace sterile old boundary drawing disputes with a
new, more fruitful, more objective investigation.
we must abandon the idea that there is one major boundary between
things with and without minds. Instead, informed by the variety of
types of computational mechanisms already explored, we must
acknowledge that there are many discontinuities, or divisions
within the space of possible systems: the space is not a continuum,
nor is it a dichotomy.
we can combine the advantages of both behaviourist and mentalist
approaches to the study of the mind. The main strength of
behaviourism, in all its forms, is that minds are not static things -
it's what they do that
is so important. But emboldened by the computational analogy we can
see that some doings are external, and some internal: operations
within a virtual machine. It is even quite possible for the internal
processes to be too rich to be revealed by external behaviour, so
that in an important sense external observers cannot know exactly
what is going on. For instance, a computer program may be able to
print out 'tracing' information reporting some of its internal
'states, but the attempt to trace the internal processes which
produce trace printing can lead to an infinite regress. A more
interesting example is a computing system with television camera
performing complex and detailed analyses on large arrays of visual
data, but with limited capacity 'output channels' so that any attempt
to report current visual processing will inevitably get further and
further behind. Here perhaps is the root of the sense of a rich but
inaccessible inner experience which has been the source of so much
TWO LEVELS OF EXPLORATION
We can attempt a two
level exploration of the space of possible minds, one descriptive the
other explanatory, though with some overlap between them.
The descriptive task is to survey and classify the kinds of things
different sorts of minds (or if you prefer behaving systems) can do.
This is a classification of different sorts of abilities, capacities
or behavioural dispositions - remembering that some of the behaviour
may be internal, for instance recognizing a face, solving a problem,
appreciating a poem. Different sorts of minds can then be described
in terms of what they can and can't do. The explanatory task
is to survey different sorts of virtual machines and to show how
their properties may explain the abilities and inabilities referred
to in the descriptive study.
explorations can be expected to reveal a very richly structured space
- not one-dimensional, like a spectrum, not any kind of continuum.
There will be not two but many extremes. For instance one extreme
will be simple servomechanisms like thermostats or mechanical speed
governors on engines. Another kind of extreme may be exemplified by
the simplest organisms.
EXAMPLES OF DIVISIONS IN THE SPACE
the important divisions between different sorts of virtual machines
are the following.
systems, like a thermostat, have only quantitative representations
of states, processes etc. For instance, a very simple organism may
be able to measure temperature, or the density of useful chemicals
in the surrounding medium. Others, like some computer programs and
people, can build structural descriptions, like parse-tree
representations of sentences or chemical formulae.
closely related distinction can be made between systems whose
internal processing consists only of continuous variation of
quantitative measures and systems which in addition can perform a
variety of discrete operations on discrete structures, e.g. matching
them, rearranging them, storing them in a memory etc. (This should
not be confused with discontinuous jumps in values of scalar
variables, as in catastrophe theory.)
systems (unlike a thermostat, for instance) have the ability to
store complex sequences of symbolic instructions. Different sorts of
instructions provide different sorts of behavioural capacities. For
instance conditional instructions are crucial for flexible, context
sensitive performance. Instructions for modifying stored
instructions may play an important role in learning processes.
systems, like conventional digital computers, can essentially do
only one thing at a time, albeit very quickly in some cases. Others
are parallel machines. The study of different sorts of parallelism
and their properties is now in its infancy. One consequence of
certain sorts of parallel architecture is the ability to monitor
(internal or external) behaviour while it is being produced. It also
permits 'postponed' conditional instructions of the form 'If ever X
occurs do Y'. This seems to be crucial to many features of human and
animal intelligence. When combined with the ability of some
sub-processes to interrupt or modify others, we find the beginning
of an explanation of certain characteristic features of emotional
parallel systems are composed of a network of serial machines
whereas others are massively and fundamentally parallel in that they
consist of very large collections of processing units, no one of
which performs any essential computing function. What would normally
be thought of as a computational state is distributed over large
portions of the network. The implications of this sort of
distinction are at present hardly understood, though it seems clear
that at least the more complex animal brains are of the massively
parallel type. The gain seems to be that for certain sorts of task,
including pattern recognition, very great speed can be achieved,
along with the ability to generalize from old to new cases and to
degrade gracefully as input information degrades. Other sorts of
task, for instance long chains of deductions, may only be achievable
on this sort of machine by indirect, clumsy and unreliable
strategies. We see here an echo of the current fashion for
distinguishing left and right brain activities: except that both
halves of the human brain seem to be massively parallel systems.
systems merely perform internal manipulations, except possibly for
receiving some input to start things off and producing some output
at the end. Others are linked to sensors which continuously receive
information from the environment, which affects the pattern of
internal processing. The 'environment' may include the physical body
in which the virtual machine is instantiated.
systems are embodied in a complex physical machine with many sensors
and motors which are controlled to perform complex actions in the
environment. Others must merely passively react to what the
environment offers, like a paralysed person.
perceptual mechanisms essentially only recognize patterns in the
sensory input. Others interpret the input by building descriptions
of other things which may have produced the input. Thus
two-dimensional images may be interpreted as produced by
three-dimensional structures, and various forms of observable
behaviour may be interpreted as produced by unobservable mental
states in other agents. Thus some systems can represent only
observable or measurable properties and relations between things,
whereas others can construct hypotheses which go beyond that given.
In particular, some can postulate that other objects may themselves
be agents with internal programs, motives, beliefs, etc., and take
these internal states into account in their own planning,
computational systems can construct formulae of predicate calculus
and perform logical inferences. Other systems lack this ability.
systems have a fixed collection of programs, whilst others have the
ability to reprogram themselves so as radically to alter their own
abilities - possibly under the influence of the environment.
systems, especially Al programs, are essentially presented with a
single goal at a time, from outside, and all they can do is pursue
that goal and sub-goals generated by it. Other systems, notably
living organisms, have a motley of motive-generating mechanisms so
that current motives, preferences, principles, constantly need to be
re-assessed in the light of new ones which may have nothing to do
with previous ones. This seems to be another of the computational
properties underlying the ability to have emotions.
systems have a fixed set of motive generators, whereas others may
have motive-generator-generators. Can this hierarchy be extended
systems can select goals for action, yet postpone action because
there will be better opportunities later. Others can only act
immediately on selected goals. The former need databases in which
postponed goals and plans are stored, and monitors which can react
to new opportunities. This ability to postpone intended action would
seem to be one of the differences between more and less
sophisticated animals, and perhaps between human infants and adults.
systems, once they have begun to execute a plan or program cannot do
anything else, whereas others can, where appropriate, interrupt
execution, and switch to another plan if necessary, and then
continue execution of the original later, if appropriate. This
requires mechanisms for storing what has been done so far and some
indication of where to continue an interrupted plan.
systems can monitor only the subsequent effects of their actions,
e.g. a thermostat. Some can monitor the behaviour itself, e.g.
placing a paw carefully on a potentially dangerous object. Some can
monitor internal as well as external processes, for instance a
computer checking which of its routines are used most frequently, or
a person detecting and classifying some emotional state. Different
kinds of monitoring provide different opportunities for
self-assessment, self-modification, self-understanding.
are merely examples of some of the more obvious discontinuities in
the space of possible explanatory mechanisms - virtual machines.
Although the descriptions are general and vague, it is already clear
how we can design machines which illustrate both sides of each of
these distinctions. We don't yet have a full understanding of all the
different ways of doing this, nor what their implications are.
Moreover, many more detailed distinctions are being explored by
computer scientists - distinctions between sorts of languages, sorts
of operating systems, sorts of algorithms, sorts of data-structures.
Eventually we should have a far clearer grasp of the structure of
this space, with some sort of global, generative, description of its
terms of such mechanisms, we can begin to account for different
abilities found in human beings and other animals, as well as
constructing machines which display such abilities. What we still
need to do is explore which combinations of mechanisms are required
to account for the characteristically human abilities which have
puzzled philosophers and psychologists and provide much of the
motivation for research in Al. A tentative list of such
characteristics in need of explanation follows:
SALIENT FEATURES OF THE HUMAN MIND
(The order is not significant)
(a) the ability to cope with varied objects in a domain
(b) the ability to cope with a variety of domains of objects
(c) the ability to perform a variety of tasks in relation to any
here is a neutral term, covering such diverse things as physical
objects, spoken or written sentences, stories, images, scenes,
mathematical problems, social situations, programs, etc. 'Coping'
includes such diverse things as perceiving, producing, using, acting
in relation to, predicting, etc.
Being able to co-ordinate and control a variety of sensors and
manipulators in achieving a task involving physical movement or
with messy, ill-defined problems and situations, and incomplete or
uncertain information; and degrading gracefully as
the degree of difficulty/ complexity/noise/incompleteness etc.
increases, rather than merely crashing, or rejecting the problem.
Degrading gracefully may involve being slower, less reliable, less
general, less accurate, producing less precise descriptions, etc.