138 Unit 4 Applied critical thinking
Suggesting explanations: plausibility
In the previous example the explanation is
grounded on good scientific evidence. If there
were any doubt about it, scientists could
measure the minerals that are dissolved in rivers;
they could test rainwater and confirm that it is
pure, and so on. But not all facts or happenings
can be explained with the same confidence,
either because they are more complex, or
because there is limited available data.
Science is not the only field in which
explanation is needed to account for facts.
Historians, for example, do not just list the
things that have happened in the past, any
more than scientists just list observations and
phenomena. Like scientists, historians try to
work out why events happened, what their
causes were. For example, take the following
piece of factual information:DOC AIn October 333 BC, Alexander’s Macedonian
force confronted the Persian king Darius III
and his army at Issus. The Macedonians,
though more disciplined than the Persians,
were hugely outnumbered. Yet, surprisingly, in
the furious encounter that followed, it was
Darius’s massive force that fled in defeat,
leaving Alexander victorious.
This is neither an argument nor an
explanation. It is simply a series of informative
claims; a statement of historical fact. However,
it is a fact in need of an explanation because, as
the text says, it is a surprising fact. Normally, if
one side in a battle hugely outnumbers the
other, the larger army wins, unless there is
some other reason for the outcome. If the larger
army wins no one is very surprised. No one is
likely to ask: How did such a big army beat such
a small one? Usually it is only when the result is
unexpected that we want to know why.
With this case, as with many other
historical events, we don’t know for certain
why or how Alexander turned the tables on
Darius. But there are many possible(the ocean), and then found that the water in
the bowl tasted salty, but the remaining water
in the jug did not, you would be right to feel
puzzled. You would probably infer that there
had been some trick, since fresh water cannot
turn into salt water just by being poured!Give a concise explanation for the fact that
rivers taste fresh and the sea salty. You may
know the reason, in which case just write it
down as if you were explaining for someone
who did not know. If you don’t know the
reason, try coming up with a hypothesis; then
do some research, on the internet or in the
library, to find out if you were right.Activity
Commentary
The scientific explanation is as follows. The
water that flows into the oceans does not all
remain there. The sun’s energy causes it to
evaporate, after which it condenses again and
falls as rain or snow. The rainwater finds its
way back into the rivers and carries more salt
down to the sea. This process goes on in a
continuous cycle (part of what is called the
‘water cycle’). The key to the explanation is
that when the seawater evaporates, it leaves
the salt and other minerals behind, so that
over an extended period of time (millions of
years) the salt becomes increasingly
concentrated in the oceans. The relatively
small amounts of salt that dissolve in a volume
of river water as it flows to the sea aren’t
enough to give it a taste. Besides, rivers are
constantly being refreshed by new rain and
melting ice or snow.
The analogy of the jug and the bowl is
therefore a bad one. It misses out the key
factors of evaporation and the large timescale.
To explain why seas are salty and rivers are
fresh, you have to include the fact that the
process has taken a very long time.