28 Unit 2 Critical thinking: the basics
This is a very simple argument. It consists of
just one reason and a conclusion, and the
connective ‘so’. The words ‘therefore’ or ‘so’
are typically used before the conclusion of an
argument, and are often called argument
indicators (or inference indicators) for that
reason.
However, this is not the only way to
construct this argument. It could have been
written:[1b] The Earth cannot be flat because (since /
given that / . . .) ships appear to sink out
of sight as they sail away from land.Note that the connective in [1b] reverses the
order of the claims. Words like ‘because’ and
‘since’ are therefore sometimes referred to as
reason indicators (or premise indicators).
(‘Premise’ is a more formal word for a reason in
an argument.)
Note also that it is not necessary to include
an argument indicator at all: the reasoning
may be just as clear without it. For example:[1c] The Earth cannot be flat. Ships appear
to sink out of sight as they sail away.The form of an argument
In each of these examples the argument is
expressed and/or arranged differently. But it is
still the same argument, with the same reason
and same conclusion. Because there are many
ways in which an argument can be expressed,
it is convenient to have one standard form for
setting arguments out. The customary way to
do this, both in logic and critical thinking, is
to place the reasons in a list, and to separate
them from the conclusion by a horizontal
line. The line performs the same function asAn argument is a complex claim used to
organise and express certain kinds of
reasoning. It is composed of two or more
claims, one of which is a conclusion; the others
are reasons for the conclusion. A good
argument is one in which the conclusion
follows from the reasons, or is justified by the
reasons.
This doesn’t simply mean that the
conclusion comes after the reasons. ‘Following
from’, in the context of an argument, means
that the conclusion is adequately supported by
the reasons. If the reasons are true, and the
argument is a good one, then the conclusion
must be true as well. Obviously a false
conclusion cannot follow, in this sense, from
true reasons.
In practical terms arguments exist for the
purpose of persuading others, or of satisfying
oneself, that a particular claim is warranted.An example
Until a few hundred years ago it was generally
believed that the world was flat. This was a
natural belief to have because the Earth’s
surface looks flat. But people had also observed
(and been puzzled by the fact) that ships
sailing away from land appeared to get lower
and lower in the water, as if they were sinking,
and appeared to rise up again as they
approached land. Some argued – from this
and other observations – that the Earth’s
surface could not be flat, but was curved. They
drew this conclusion because if the Earth were
flat, a ship would just appear to get smaller
and smaller until it was too small to see. The
argument went like this:[1a] Ships appear to sink out of sight as they
sail away. So the Earth cannot be flat.