| Evaluating Explanations | |
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Fallacies in Causal Reasoning |
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There
are some common mistakes that are made in proposing causal explanations.
Here are a few of the best ones: Confusing
Correlation and Cause Take the case of the method of concomitant variations that we’ve just been looking at. The method involves going from observation of correlations to suppositions of causal relationships; but it is a fallacy to suppose too hastily or without sufficient care that if property F is observed to be correlated with property G then F is the cause of G. Even
if the correlation is strongly supported by the data, thus establishing
a strong inductive argument from the data to the correlation, the move
from correlation to cause can be problematic. There are many ways in which this
deduction can be fallacious. a.
Coincidence The correlation may be purely coincidental! Example An inference from the strong positive correlation
between Holland's birthrate and the number of stork's nesting in
chimneys would be fallacious. In fact, though correlated, there is no causal
connection at all it seems. The correlation appears purely accidental. Example Is an inference from the strong positive correlation
between an individual's level of literacy and their participation in
volunteer work to a causal connection from the former to the latter
fallacious or not? (In the inaugural lecture of the Keith Murdoch
Oration, hosted by the State Library of Victoria, October 11, 2001,
Rupert Murdoch claimed such a causal connection as part of an argument
for the importance of higher education and corresponding need for
increased funding. The enthymematic implication of the claimed causal
connection was that higher literacy, achieved through education, causes
a social good which, in conjunction with the suppressed premise that we
should pursue social goods, implies that we should
endeavour
to increase literacy and thus ensure proper funding for education.) b.
Symmetry Correlation is symmetrical – F is correlated with G
if and only if G is correlated with F so the same correlation would
justify the conclusion that G causes F. Example
Consider the positive correlation between time spent in hospital
and risk of death.
Does the risk cause one to spend more time in hospital or does
spending more time in
hospital cause an increased risk of death (due to non-treatable
infections found in
hospitals)? c.
Common
cause It may be that neither is the cause of the other, but
that both are the effects of some other property H. Example Does the El Nino effect cause drought in Australia or might both El Nino and drought in Australia be caused by some third factor? Their positive correlation does not answer this question.
Example An inference from the strong positive correlation
between shoe-size and quality of handwriting to some causal connection
between them would be fallacious (and there is no accepted theory which
would suggest such a connection). In fact they are correlated by virtue
of their having a third common cause — maturity. d.
Reflexivity There may be a complex causal interrelationship of F
and G such that F is to some extent the cause of G and G is also the
cause of F. Example Is a chicken the cause of an egg, or is an egg the
cause of a chicken. There are any number
of positive feedback loops in the ecology. Any one of these could probably serve as an example
here. e.
Insignificance The causal relation may be real but insignificant, in
which case P may contribute to Q but it could not be claimed to be the
cause of Q. A
similar fallacy can also arise in connection with uses of the Sufficient
Condition Test and the Necessary Condition Test. Example Suppose (as was claimed in the Australian yesterday)
that homosexual males are discovered to have a certain brain property X.
Having brain-property X is a necessary and sufficient condition for
being a gay male. (In this case it was found that women and homosexual
men registered a reaction in the anterior hypothalamus when tested with
4, 16-androstadien-3-one, but women and heterosexual men did not.) The mere correlation of being a homosexual male with
the presence of brain-property X doesn't necessarily show that this
brain property causes sexual orientation (nor has it been suggested this
time). Only a correlation has been established and this might well be
explained by means of something other than a causal connection between
sexuality and the brain-property. It might turn out that both
homosexuality and the brain-property X have a common cause in biological
and environmental factors. Post Hoc Ergo
Propter Hoc Also
known as simple Post hoc. The Latin
tag just means ‘after this therefore because of this.’ A fallacy of
supposing that because event G follows event F in time that therefore
event F causes event G. Of course, there is no such necessary
connection. Although, as I said earlier, we do expect that if F is the
cause of G then F will precede G temporally. Which is to say that if G
precedes F we think that it is absurd to suppose that F is the cause of
G. (Naturally none of this applies in advanced Physics.) Example Egyptians used to worship the ibis (a bird) because
each year, shortly after flocks of ibis had migrated to the banks of the
Nile, the river overflowed its banks and irrigated the soil. The
Egyptians believed the ibis caused the floodwater, when, of course, both
the birds’ migration and the river’s overflow were attributable to
the change of season.[1]
[1] Soccio/Barry, Practical Logic p. 347 |
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Evaluation of Explanations |
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Bearing
in mind the very different function that an explanation has from an
argument, it is not surprising that the criteria which are of interest
to us in evaluating the two are quite different. What makes a good
explanation depends upon the particular use that the explanation is
intended for, but there are two principal factors to be considered: a.
Plausibility. How
likely is it that the explanans will be true? b.
Power. Can
the explanans actually cause the explanandum? These
are pretty obvious criteria and don’t need too much explanation by me,
but there are many other factors that should be considered in deciding
whether we have a ‘good’ explanation or not. There are any number of
different lists of desirable criteria, and it’s an area of ongoing
dispute amongst philosophers of science, but here is a list that is
taken from a well-known introductory text.[1]
c.
Simplicity. Is
the explanation overly complex? We should prefer the simplest possible
explanations. (Look up ‘Occam’s Razor’) When one has a choice of
two explanations then one should, other things being equal, choose the
simplest one. Do you think that that will ever lead you to choose the
false theory over the true theory? Example The classic example here is the competition between
the Ptolemaic and the Copernican theories. Both of these theories
predicted the motions of the heavenly bodies fairly well, but the
Copernican theory did it much more simply. d.
Generality. Can
the same explanation help us to understand a wide variety of other facts
about the world? The more it explains the better – but if it tries to
explain everything it may end up explaining nothing. (This
is the problem of ‘unfalsifiability’ we’ve talked about before.) Example Consider the fact that the east coast of South
America looks like it fits rather nicely into the west coast of Africa.
This was for a long time treated simply as a curiosity, but Alfred
Wegener proposed an explanation for it which involved the continents
floating about the seas like leaves on a pond. This was dismissed as
absurd for a very long time – in fact it didn’t seem to achieve
uniform acceptance in the scientific community until about the 1960s.
Part of the reason that Drift was accepted by some was that it allowed
explanations of the distribution of certain types of flora and fauna. It
is surprising to think that so recently the only alternative theories to
explain this sort of thing appealed to vanished land bridges which had
left no other trace. e.
Modesty. Does
the explanation require us to change too much of what we think we
already know about the world? The less we change the better –
intellectual laziness can be a virtue. Great changes require great
justifications, but they are possible; for example, it has been
suggested that to understand some quantum physical facts we need to
change our beliefs about logic. Example If I might just continue with the continectal drift theory; one can certainly imagine why the theory would be resisted. At the time it was the general opinion that land was land and didn’t float about the place. What could be more solid than a mountain range? In order for the Drift theory to be acceptable, and for the malleability of the continents to be accepted, it was necessary for a great deal of evidence from many different fields to be accumulated so that any lternative theory to explain all the observations was more disruptive of the general world view than the Drift theory. Example It wasn’t that long ago that Lyell had to
fight to have his claims about the gradual nature of geological change
accepted. Everyone knew that the world was created at 9am of October the
10th 4004 BC, so an explanation of sedimentary rocks that
involved their compaction over tens o thousands of years or even more
was quite unacceptable.
[1]
I. M. Copi, Introduction to
Logic (many editions).
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Criticism of Theories |
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These
criteria for what constitutes a good explanation are only suggestive.
When an explanation involves a theory – as for example the theories of
natural selection or evolution are involved in the explanation of why
there are so many different varieties of finches on the Galapagos
Islands - that theory may be contrary to many of those criteria without
being necessarily a bad theory. But that would
give us reason to prefer some other theory if one were available.
This being the case it’s clear that we’d like to have some rules of
thumb that we can apply to the evaluation of theories. We shall have a
look at four ways of criticizing theories – well five actually.[1] a.
Is
there something to explain? The
very first criticism needs to be directed at the phenomenon that the
theory is supposed to explain. We have to be sure that there really is
something there. Naturally if the phenomenon that is claimed to be in
need of explanation doesn’t actually exist or occur, then any
explanation of why it occurs is going to be false. Example Many disputes over global warning stick at this very
first hurdle. Why, it is asked, are the Pacific islands sinking?
Obviously, it is because anthropogenic global warming is melting the ice
all around the world and raising the sea level. Well not so fast, say
critics of GW: there isn’t any evidence that your islands are
actually sinking. The recorded rate of sea level rise indicates that if
the sea is rising it is rising at an extremely unalarming rate, and that
this rising is no worse now than it has ever been. To suppose that the
entire globe is warming due to industrial pollution is therefore
unnecessary. Of
course, a criticism such as this, which denies that there is anything to
explain, has to deny all the significant evidence that the proponent of
the explanation adduces. In the example, the opponent of the AGW theory
has denied that there is significant sea-level raising that needs to be
explained, but the AGW proponent may admit that and yet think that
something needs to explain the retreat of the glaciers, the bleaching of
the coral reefs, the decline in polar bear populations, etc. The AGW
opponent has to either deny all these facts, or deny enough of them so
that the remaining facts no longer provide sufficient support for the
theory. b.
Is
there a plausible alternative theory? But
suppose that we do accept that the data support the existence of some
phenomenon in need of a theory to explain them; does it follow that we
have to accept the theory that the proponent presents? Of course not. If
there is another plausible theory that explains the same thing we have
to then make a comparative evaluation of the two theories and we pick
the more reasonable of the two. In any case, if there are two theories
that explain the same phenomenon then the fact that the phenomenon
occurs isn’t such strong evidence that the proponent’s theory is
true. Example Consider AGW again, and suppose the facts that remain
are sufficient to suggest that there is indeed some GW going on. Does it
follow that the only explanation must be that CO2 produced by
industrial processes is producing a marked increase in the greenhouse
effect that will make Earth inhospitable? Not at all. The AGW skeptic
may suggest that the same GW effect might be caused by variations in
solar activity, or by alterations in the Earth’s orientation. And
given that the Earth’s temperature has varied hugely over time – and
that anthropogenesis is not plausible in most cases – it might be
thought that another theory that can also explain all those other
changes is to be preferred. c.
Are
the theory’s predictions good? As
I said before, there are at least two things that a theory is supposed
to be able to do. In the first place it has to explain the things that
have already happened, and in the second place, if it is a good theory,
it should also tell us what is going to happen next. To be more precise,
it should make predictions about what we can expect to observe in
certain specific circumstances if the theory is true. If the predictions
that the theory makes are not fulfilled then that is prima facie
a reason to disbelieve the theory. The sorts of predictions that are
especially to be looked for are those which make predictions about
things that the theory wasn’t specifically designed to explain.
Example Some of you may be aware that there used to be a
theory that light was a wave phenomenon in just the same way that sound
was. If that was the case then there had to be some medium in which the
wave travelled. We are familiar with waves in water, and by analogy we
can think of waves in air (sound waves) being the same sort of thing:
but you can’t think of waves in that sense without there being
any water or air. Clearly then there has to be something for light to be
propagated in. This thing was called ether. This led to the idea
for an experiment: if the Earth moves through this ether then light
travelling in different directions will appear to move at different
speeds. (Imagine something travelling in water with or against the
current.) An experiment to demonstrate this was designed and carried
out, and – legend goes – failed to give the expected result.
Example Consider again the AGW theory. This theory has
certain forms in which models are constructed of the atmosphere and the
effects of additional CO2 are predicted from the model. Some
of these models give a very good match for some periods of history for
which temperature records are available, and so they are taken to be
‘good’ models of atmospheric processes. These models predict that
additional CO2 in the quantities that industry has added to
the Earth will caause warming. So far so good. But GW critics also note
that the models predict that warming will occur first and massively in
the atmosphere before any warming is observed on the ground. This, they
say is exactly the opposite of the observations that the proponents of
AGW accept. d.
Does
the defence of the theory seem rather ad hoc? Any
theory is going to be criticized, and there may be contradictory data
that need to be explained that the theory in its originally presented
form just cannot explain. One of the clues that a theory is in trouble
is that the additions or modifications of the theory have no
justification other than the need to account for anomalous observations.
They don’t really represent a refinement of the theory so much as
repairs. Example The classic example of this was the development of
Ptolemaic astronomy. That theory proposed that the Earth was static and
the planets, moon, and sun moved in circles about it. It was quickly
discovered that the motions of the celetial bodies could not be properly
predicted with this simple model – in particular the retrograde
apparent motion of Mars was impossible – and so bits and pieces were
tacked on. Instead of the planets travelling in cycles, they now also
moved on epicycles. And those epicycles had other cycles to ride upon
‘em, so that the original scheme of
incorruptible bodies travelling at constant speed on perfect
geometrical paths became quite lost. The obvious fact that the original
principle of celestial perfection was sacrificed to the observational
necessities gave a name to this sort of theoretical revision. It is
called saving
the appearances. e.
Is
the theory testable? The
final criterion is something we looked at previously: it must be
possible to test the theory. If there is no outcome that isn’t
explicable by this theory then the theory doesn’t tell us anything
about the possible ways that the world could be, and so it is probably
not telling us anything about how the world actually is. Of course, just
because a theory isn’t useful in this sense doesn’t mean that it’s
necessarily false – unless you take a particularly strong view of what
it is to be a theory, which I’m not going to do. For example,
there may very well be a God even if the theory that there is a God
turns out not to be a very useful explanation of things.
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