264 Unit 7 Critical reasoning: Advanced Level
a reason for arguing that it is true. Not
surprisingly, reasoning of this kind is known
as argument (or inference) to the best
explanation. As this is a mouthful, we’ll
shorten it to ABE. (It has also been given the
name ‘abduction’.) ABE or abduction is not
found only in science. It is actually one of
the commonest ways in which we reason in
everyday situations; so much so that we are
often barely conscious that we are reasoning
at all. A classic example is my coming out of
the house in the morning and finding the
ground in the garden soaking wet. If it had
rained heavily in the night, that would
explain this observation simply and
plausibly; so I take it that it has rained, and
think no more about it. In fact, if it had not
rained in the night, I would be very
surprised.
ABE is a powerful and familiar method of
reasoning. But as we have seen in several
previous chapters, it carries a high risk of
jumping to conclusions. It therefore has to be
used and evaluated with care. ABE supports
hypotheses; it does not establish facts. Recall
the example of the origin of ‘posh’ (Chapter
4.2, page 141). The claim that it was an
acronym from ‘Port Out, Starboard Home’
seems such a plausible explanation that it is
often accepted without further thought. It
turns out there is little evidence to support it
other than its elegant explanatory properties.
So, we must either abandon it or look for
additional supporting evidence. ABE is not
sufficient on its own to make an inference
safe. Returning to my wet garden: if I later
discovered that the ground everywhere else
in the neighbourhood was dry, I would
obviously have to think again about the
seemingly obvious inference that it had
rained in the night. To explain the dry
ground elsewhere, as well as my wet garden, I
would need a more local explanation such as
a burst water pipe.relatively recently combustible materials were
believed to contain a mysterious
undetectable substance called ‘phlogiston’,
which they gave off when they burned, to be
absorbed by the air. The reason the candle
goes out was thought to be that the air in the
jar could only absorb so much phlogiston:
quite the reverse of the oxidation theory that
we now learn at school. One problem with
the phlogiston theory was that burning
should have resulted in a loss of substance to
the air, and hence a loss of weight. The
discovery that combustible matter when
burned gained weight was the beginning of
the end for the theory – although some
scientists clung to it by claiming that
phlogiston had negative weight, making it
even more mysterious.
The idea of phlogiston was accepted for
centuries because at the time it seemed to
explain combustion. It was the best
explanation around, until oxidation was
understood. The argument for phlogiston was
that if there were such a substance, it would
explain why the candle went out in a
confined space. It did not, however, explain
why burnt matter (ash etc.) gained weight
without extra complications such as negative
mass. Nor could it explain, simply, why the
water level rises in the jar. If phlogiston were
added to the air during burning, then
arguably it should have forced the water level
down! You will recall (from Chapter 4.2) that
explanations are generally assessed by their
scope (how much they can explain) and their
simplicity. Once understood, the theory of
oxidation explained more than phlogiston
did, and much more simply. It didn’t need
implausible extra accounts as to why it
couldn’t be detected, or weighed less than
nothing. The argument for oxidation is
therefore much more compelling.
The fact that something is the best or
most believable explanation is often used as