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Up: 2. Dispositions
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2.4 Scientific Explanation of Dispositions
Usually we expect more of dispositions than the mere holding of a
conditional relating a circumstance to a result. We expect that the
disposition has some scientific explanation in terms of some
other properties of the object involved. The holding of a `minimal
disposition', we think, points to some deeper explanation in terms of the
causal features of the object and/or its parts. Science, it seems, cannot
simply accept an explanation of an object breaking in terms of just its
`fragility', of an plant seeking light in terms of just its
`phototropism', or the sleep-inducing powers of opium in terms of
merely its `dormative virtue'. Dispositions are very often regarded by
the scientist as merely a sign that he has to work harder, to find the
underlying structures and their causal relations. This process of finding
explanations of observed dispositions in terms of constituents has been
spectacularly successful in an enormous range of cases (but not all, as we
shall see).
The solubility of salt is explained by the facts that salt is made of two
ions Na+ and Cl-, and that these constituents interact in
such a way with the H2O molecules in liquid water that they become
separated from each other and move more freely around the liquid. The
flexibility of a piece of metal is explained in terms of the arrangement
of the metal atoms in the semi-crystalline structure of the metal, paying
particular attention to any defects or departures from a strictly regular
form. The temperature of a substance can also be regarded as a
dispositional property as it is the ability to transfer heat to
neighbouring bodies, but it can be explained well in terms of the speeds
of motion of the atoms and molecules within that substance. The `dormative
virtue' of opium might find explanation in terms of the effects of the
morphine in opium on, perhaps, the rate of release of neurotransmitters in
the nervous tissue in the brain.
In all these cases, the explanation in terms of parts and their behaviour
produces a better account of the disposition than the mere stating of the
conditional which defines the disposition in the first place. The
explanation in terms of microscopic structure explains exactly how and why
the observed disposition arose in the first place, and is often more
accurate in explaining the usual slight deviations from a preliminary
conditional statement. The solubility of salt, for example, may turn out
to depend on temperature, and this new feature may be well explained by
the microscopic explanation in terms of ions and water molecules.
Scientific endeavour is continually interested in drawing together the
explanations of many different observed dispositions as the result of some
fixed underlying structure of the objects concerned. Science, indeed,
measures its success in describing the data when causal explanations are
given along these lines. It always looks for a basis of dispositions,
which (as Quine
2.5
puts it), is `a hidden trait of some sort  that inhered in the
substance and accounted for' the manifestation of the dispositions.
As the result of progress in science, we have come to expect that
all dispositions, powers, virtues etc., can be explained in
terms of a structural basis of some kind. It is a common belief that
modern science does away with those obscure notions of `disposition'
and `potentiality', in favour of an analysis of the component
structure of the things concerned, and their functional relationships.
Science, it is often said, cannot long accept an explanation of an object
breaking in terms of just its `fragility', or of an plant seeking
light in terms of just its `phototropism'. Dispositions, so popular
opinion has it, are regarded by the scientist as merely a sign that he has
to work harder, to find the underlying structural forms and their
relations.
Talk of `dispositions', `powers', and `capacities' seems to be talk of
`occult powers' which are somehow not sufficiently definite for
a hard-nosed scientific explanation. There seems to be something
intrinsically unsatisfactory and vague about a property that may or
may not operate, and in particular it seems uncertain how to
describe them rigorously and mathematically. It took science a long time
to accept the reality of electric and magnetic fields, for example, as,
although they turned out to have good mathematical descriptions, they are
dispositional entities in an essential sense.
Physicists hoped for a long time that some purely mechanical explanation
could be found for electromagnetic phenomena, and developed theories of a
extremely rigid mechanical aether, but in the end they have
tended to accept fields as some kind of thing which exist sui
generis.
In the next section, however, I will argue that, despite the apparent
successes of science, there can be no reduction of
dispositional properties to purely static or structural properties.
Next: 2.5 Are Bases ultimately
Up: 2. Dispositions
Previous: 2.3 Are Dispositions Real?
Prof Ian Thompson
2003-02-25
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