Minds and Computers : An Introduction to the Philosophy of Artificial Intelligence

soma
dendrites
myelin sheath
synapse
axon
Figure 4.4
Model neuron.

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di
fference in electrical potential between the inside of the cell and the
outside of the cell rises. When this potential di
fference is high enough,
the soma will discharge an electrical impulse along its axon and return
to its resting potential. This is something of a simplification but it
su
ffices for our purposes.
If you’re feeling a little overwhelmed with all these technicalities and
all this new terminology, don’t fret. All you really need to take away
from this chapter with respect to the operations of neurons is the fol-
lowing.
There are very many neurons in the brain which are highly inter-
connected. These neurons function by passing electrical signals to
each other. If a neuron receives su
fficient incoming signals from other
neurons, it will send out a signal of its own.
Those readers who are intrigued by what they’ve read here and
would like to learn more are advised to follow the suggestions for
further reading.
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  
Figure 4.5
Model synapse.
synaptic cleft
pre-synaptic terminal
Axon
post-synaptic structure
synaptic
vesicles

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C H A P T E R 5
AUSTRALIAN MATERIALISM
Now that we have at least a rudimentary understanding of just what
an amazing thing the human brain is, it is time to examine a philoso-
phical theory which posits a very strong connection between the
neural and the mental.
Australian materialism – so called as its major proponents were
located in Australian universities – is a theory which goes by many
names. It is variously also known as reductive materialism, identity
theory, type physicalism and central state materialism, for reasons
which will become apparent in due course.
It will serve our purposes here to develop Australian materialism
in conjunction with another theory: the causal theory of mind.
When we ask the question ‘what are mental states?’, there are two
distinct kinds of answer one can provide. One kind of answer involves
giving a conceptual analysis of mental states – an account of what we
mean by ‘mental states’. Another kind of answer involves providing a
substantive identification – indicating which things turn out to be
mental states.
In the case of behaviourism, these two kinds of answer to the ques-
tion of what mental states are were conflated in the one theory. This
is because behaviourists are eliminativists about mental states and,
hence, do not believe there is a substantive identification to be made.
They hold that talk of mental states is, in fact, just talk about dispos-
itions to behave – behaviourism is an ontologically eliminative and
semantically reductive theory of mind.
We’re now going to employ more philosophical sophistication and
carefully tease apart the two ways of answering the question of what
mental states are. Australian materialism will provide us with the sub-
stantive identification – the account of which things turn out to be
mental states. The account of what it is to be a mental state, however,
will be provided by the causal theory of mind.
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5.1 THE CAUSAL THEORY OF MIND
The canonical exposition of the causal theory is given by David
Armstrong in his 1968 monograph, A Materialist Theory of Mind.
Armstrong, together with J. J. C. Smart and U. T. Place, is one of the
three major figures associated with Australian materialism.
The causal theory, as we have said, aims to give an account of what
it is to be a mental state. This is, if you will, very much like providing
a job description for mental states. A job description does not specify
the race, age or gender of the occupant of the role. It merely tells us
what the relevant duties are – what one has to do in order to fill the
role. So it is with the causal theory – it tells us what something has to
do in order to fill the role of a mental state.
We begin by reflecting on the fact that many terms in our language
are defined by reference to their causal powers. The term ‘poison’ is a
paradigm example. A poison can be a liquid, a solid or a gas. Poisons
can be coloured or colourless; they can be odourless or have a
distinctive odour, and so on. None of these properties are relevant to
whether or not the substance in question is properly called ‘poison’.
What makes a substance a poison is its causal role with respect to
bringing about ill health in humans. To cast this as a definition we can
say the following: a substance is a poison i
ff it is apt to cause ill health
in humans.
The central tenet of the causal theory is that mental state terms are
just such terms. We define mental state terms, according to the causal
theorist, by reference to their causal role with respect to behaviour.
This allows the causal theorist to provide a schema for defining