7.2 Soundness and validity: a taste of logic 261
Summary
• The soundness of an argument depends
on two factors: (1) the truth of the
reasons; and (2) whether or not they
adequately support the conclusion.
• There are different standards for judging
(2), depending on the type of inference
being made.• The highest standard for judging (2) is that
of deductive validity. But there are other
standards by which to judge the reliability
of an argument.flying on to Argentina tomorrow, and
he will not be back until next week.
Therefore he is not corrupt.
4 Suggest a conclusion – if there is one –
which can validly be drawn from each of
the following sets of premises. If it is valid,
show or explain the form that the argument
would take.[A] If an athlete has accepted prize or
sponsorship money, that makes
him or her a professional.
Nathan is sponsored by a major
software company. So...
[B] If an athlete has accepted prize or
sponsorship money, that makes
him or her a professional. Eunice
is not a professional. So...
[C] If an athlete has accepted prize or
sponsorship money, that makes
him or her a professional. Abbas
has not accepted any prize or
sponsorship money. So...Answers and comments are on pages 339–40.1 Are either, neither, or both of these two
arguments sound – and why?[A] Citrus fruits have a sharp, acidic
taste. Lemons taste sharp and
acidic. Therefore lemons are citrus
fruits.
[B] Citrus fruits have a sharp, acidic
taste. Lemons are citrus fruits. So
lemons have a sharp, acidic taste.
2 Comment on the following argument.A real diamond is so hard it will
scratch glass. But when we drew a line
on the glass with the stone in your
ring it didn’t leave any mark at all,
however hard we pressed. Therefore it
is not a real diamond.
3 What can you say about the soundness of
this argument?If the vice-president were guilty of
corruption, as you say he is, he would
be in prison, not on an official state visit
to South America. He is not in prison.
In fact he is in Chile right now and isEnd-of-chapter assignments