Identifying flaws in argument

Identify the flaws in the following pieces of reasoning:
1 A fantastic basketball team could be created if the best player from each of the best
teams formed a new club. Basketball would then become an exciting game for fans
everywhere.
(Law School Admission Test, October 1985)
2 Crimes and outrages of all sorts have been committed under a full moon by a wide
variety of people. The advice to derive from this is clear: when the moon is full, trust
no-one, not even yourself.
(Law School Admission Test, September 1984)
3 Young people today have more formal education than their grandparents had.
Wilma is young, so she must have more formal education than her grandparents had.
(Law School Admission Test, 1982)
4 Neither marijuana nor LSD can be harmful, since they are used by doctors to ease
the pain of cancer patients.
(Law School Admission Test, 1982)
5 Adolescents frequently suffer from anaemia, but this is not, as is often supposed,
due to insufficient iron in their diets, but is a result of this group’s having a higher
requirement for iron than that of the rest of the population.
(Law School Admission Test, February 1983)
6 We know that diet is an important cause of disease. One example of a disease which
is attributable to diet is the heart attack, which is so common in Western countries.
In countries with different diets, the diseases differ also. For example, in Japan the
most common fatal diseases are strokes and cancers of the stomach. The Japanese diet
has a much lower fat content and a much higher fibre content than the Western diet.
So if people in the West were to adopt a Japanese low-fat/high fibre diet, they would
be unlikely to die from heart attacks. They would die instead from the diseases which
are common in Japan – that is to say, strokes and cancers of the stomach.
7 Who invented cooking? Since cooking requires heat, the first cooks must have used
fire. Until recently, there was no evidence of fire having been used earlier than
200,000 years ago. But now, reliable scientific evidence has shown that the ancestors
of Homo sapiens were lighting fires almost 400,000 years ago. So cooking must have
been invented at that time.
8 The witness said that he had seen Fred in the vicinity of the shop at the time the
fire was started. But we know this witness has a grudge against Fred, and he has
been known to give unreliable evidence in the past. So we cannot rely on this
person’s statement. Hence Fred must have been somewhere else when the fire was
started.
9 Most people could be musical geniuses if they practised hard enough. A psychologist
interested in whether genius is mainly hard work rather than inspiration has
examined the lives of seventy-six composers. Most of them had at least a decade of
painstaking training before they wrote any masterpieces. Mozart, for example, was
drilled incessantly by his father in techniques of composition before he composed his
first work of genius at the age of 12.
10 Some people claim that poverty is one of the causes of crime. But there can’t be any
kind of link between being poor and committing crimes, because lots of people who
are poor never commit a crime.
11 A large study in Norway found that those people who scored highly in tests of anxiety
levels were the people most likely to be suffering from pre-malignancies, i.e.
abnormal cells that are likely to become cancerous. Thus it is evident that if anxiety
states could be more easily diagnosed and treated, the incidence of cancer would fall.
12 In 1976 Richard Dawkins’ book The Selfish Gene was published. He chose to describe
genes as ‘selfish’ because they are self-replicating. Because genes are the building
blocks of human beings, many people have taken his book to suggest that human
beings are by nature essentially selfish. Given the date of its publication, and its
widespread popularity, it is evident that it gave rise to the ideas underlying the 1980s
period of unbridled market economics, when selfishness amongst consumers and in
business was regarded as beneficial for society.
13 Was the universe created by an intelligent designer, as some religions claim? The
way in which an intelligent being would design a universe would be to keep it simple.
But we inhabit a hugely, and possibly unnecessarily, complex universe. So we can
conclude that the being who designed the universe was not intelligent.
14 When research has been done into the effect of diet on health it has often failed to
find anything conclusive about a connection between the two. The usual explanation
is that it is impossible to draw reliable conclusions, because it is difficult to get
research subjects to stick to a particular diet. But the conclusion that should be drawn
is that there is no link between diet and disease, because then we could stop worrying
about our diet, and focus on lifestyle changes that really would improve our health,
such as not smoking, cutting down on alcohol, and increasing the amount of exercise
we take.
15 People often have the experience of thinking about someone, and then shortly afterwards
receiving a phone call from that person. This is exactly what would happen
if telepathy were operating. So, despite the claims of sceptics, telepathy clearly is
possible.
 Identifying flaws Answers:

1 This passage asserts that a fantastic basketball team could be created, and concludes
from this that the game would thereby become exciting for fans everywhere. We may
doubt whether it is true that a fantastic basketball team could be created if the best
player from each of the best teams formed a new club. All these ‘best players’ may
have identical rather than complementary skills. However, we are not concerned with
evaluating the truth of reasons in this exercise, so we should ask ‘If it is true that a
fantastic basketball team could be created if the best player from each of the best teams
formed a new club, does it follow that basketball would then become an exciting game
for fans everywhere?’ No – the evidence that a basketball team composed of extremely
talented players could be created is insufficient to show that this would produce an
exciting game for spectators. Perhaps it would not be exciting to watch one superteam
playing against weaker opposition, and perhaps the excitement of basketball for
fans depends upon seeing one’s home team as having a chance of winning.
2 This is an example of the flaw of assuming that because two things have occurred
together, one has caused the other. The fact that crimes have been committed when
the moon is full is not a good reason to believe that the full moon causes people to
commit crimes.
3 This argument draws a conclusion about one individual from evidence about
what is generally true of members of the group to which that individual belongs. If
we took the first sentence to mean that every young person today has more formal
education than their grandparents had, then the conclusion about Wilma would
follow. But it is more reasonable to construe the first sentence as meaning that in
general young people today have more formal education than their grandparents
had. If that is the claim, then there may be exceptions and Wilma may be one of
those exceptions. Perhaps her grandparents were unusual in their generation in
having a university education, and perhaps Wilma dropped out of education at an
early stage.
4 The conclusion is that neither marijuana nor LSD can be harmful. The reason given
for this is that doctors use them as painkillers for cancer patients. The conclusion
does not follow, since doctors may have to use drugs which are harmful when the
alternative – leaving the patient to suffer severe pain – is worse.
5 This passage tells us that adolescents have a higher requirement for iron than that of
the rest of the population. It concludes from this that the reason why adolescents
often suffer from anaemia is not that they have insufficient iron in their diets.
However, if their requirement for iron is greater than normal, it is much more
reasonable to conclude that their anaemia could be caused by insufficient iron in their
diets. There is a question about the meaning of ‘insufficient’ in the conclusion.
Adolescents suffering from anaemia may have an amount of iron in their diets which
would be sufficient for all other people. But if their requirement for iron is greater,
then this amount will be insufficient for them.
6 This argument concludes that if people in the West switched to a Japanese diet,
then instead of dying from heart attacks, they would die from the diseases which are
the most common causes of death in Japan. It bases this conclusion on two claims –
that diet is an important cause of disease, and that heart attacks in the West are
caused by diet. However, the evidence is insufficient to establish the conclusion, since
diet may be an important cause of disease without being the only cause of disease.
Hence the diseases common in Japan may be caused not by diet, but by genetic
factors, or by environmental conditions. The passage does not settle the question as to
what causes strokes and cancers of the stomach amongst the Japanese. So we cannot
be confident that changing to a Japanese diet would increase the incidence of these
diseases amongst Westerners.
7 This passage concludes that cooking must have been invented 400,000 years ago,
based on the evidence that fires, which would have been necessary for cooking, were
being used at that time. But the passage establishes only that fire was necessary in
order for cooking to be invented, not that it was sufficient. Perhaps the first use of fire
was for warmth or to deter predators, and maybe cooking was not invented until
some time later. This is an example of a common flaw – that of treating a necessary
condition as if it were a sufficient condition.
8 This passage argues from the unreliability of a witness to the conclusion that what
the witness said must have been false. But the evidence is insufficient for us to draw
this conclusion. The most we can conclude is that Fred may not have been in the
vicinity of the shop when the fire was started. Without further evidence we cannot
conclude that he must have been somewhere else.
9 The conclusion of this argument is that most people could be musical geniuses if
they practised hard enough. The evidence offered for this is that a number of composers
(presumably musical geniuses) wrote their masterpieces only after a long
period of training in composition. Two questionable moves have to be made in order
for this evidence to be taken to support the conclusion. First it must be assumed that
the practice which these composers had was necessary in order for them to write
masterpieces. Maybe this is not too wild an assumption, but it is just possible that it
was not practice, but maturity, which was required in order for them to write masterpieces.
The more serious flaw is to conclude that because some people could write
masterpieces as a result of practising hard, anyone could do so if they practised hard.
This is to treat the necessary condition of practising or training in composition (if
we concede that it is a necessary condition) as a sufficient condition for composing
masterpieces. Perhaps what is also needed is a certain talent which not everyone
possesses.
10 This argument concludes that there cannot be any link between being poor and
committing crimes. The evidence it produces for this is that many poor people never
commit a crime. But this evidence is insufficient to establish the conclusion. Even if
many poor people never commit a crime, it may be true that some poor people who
do commit crimes would not have done so if they had not been poor. So there could
be a link between poverty and crime such that poverty makes some people more likely
to commit crimes.
11 In drawing the conclusion that diagnosis and treatment of anxiety states would
reduce the incidence of cancer, this argument is assuming that suffering from anxiety
causes cancer. The evidence offered – a study in which those identified as highly
anxious were more likely to have the first signs of cancer – shows only that there is a
correlation between anxiety and cancer, not that anxiety causes cancer. It is possible
that some third factor, for example, stress, causes both. It is also possible that anxious
people are more likely to smoke, and that smoking caused the pre-malignancies
suffered by the subjects in the study.
12 This argument concludes that ideas in a book must have given rise to ideas underlying
a particular attitude in society, on the basis that both were about human
selfishness, and that this particular attitude in society followed the publication and
popularity of the book. This is flawed because the fact that x occurred after y is
not evidence that y caused x. This kind of fallacy is sometimes referred to by a
Latin phrase – post hoc ergo propter hoc – which means ‘after this, therefore because
of this’.
13 The argument concludes that the being who designed the universe was not intelligent,
based on claims that the universe is hugely complex and that an intelligent
being would design a simple universe. If we were to accept the truth of these reasons,
then we should conclude that the universe was not created by an intelligent designer,
which implies that either the designer of the universe was not intelligent or the
universe was not created by a designer. The argument is flawed because it concludes
simply that the designer of the universe was not intelligent, and ignores the possibility
that the universe was not created by a designer.
14 The argument concludes that the conclusion that should be drawn is that there is no
link between diet and disease. In doing so it rejects the usual explanation of the
failure of studies to find anything conclusive about a connection between diet and
health. However, it gives no reason for rejecting this explanation, so there is no
support for the conclusion in this section of the passage. What it gives as a reason for
accepting that there is no link between diet and disease is that if we did accept this
we could stop worrying about diet and focus instead on lifestyle changes that would
improve our health. The flaw is that accepting a particular belief because it would
make us feel better, or be more convenient, or allow us to focus on something more
important cannot be a good reason for thinking that the belief is true. A distinction
can be made between having a motive for believing something, and having a reason
for believing something, and motives are not good reasons for belief.
15 This argument concludes that telepathy is possible, on the grounds that if telepathy
were operating, people would have a certain experience, which people do in fact often
have. The flaw is that the argument ignores the possibility that these experiences
could be caused by something other than telepathy, even if it is true that if telepathy
were operating, these experiences would occur.