Identifying assumptions in arguments

For each of the following passages, identify any unstated assumptions, and say whether
they are assumptions which underlie a basic reason, or assumptions which function as an
additional reason, or assumptions which function as an intermediate conclusion.
1 Men are generally better than women at what psychologists call ‘target-directed
motor skills’, but what the rest of us call ‘playing darts’. Many people would say that
this is not due to innate biological differences in the brain, but is due to the fact that
upbringing gives boys more opportunities to practise these skills. But there must
be some innate difference, because even three-year-old boys are better than girls of
the same age at target skills.
2 Allowing parents to choose the sex of their children could have serious social costs.
There would be a higher percentage of males who were unable to find a female
partner. Also, since it is true that 90 per cent of violent crimes are committed by
men, the number of violent crimes would rise.
3 When people live in a house for a long period of time, they develop a strong
commitment to the local neighbourhood. So a fall in house prices may have a
beneficial effect. The middle classes will become enthusiastic campaigners for better
schools, and against vandalism, traffic congestion and noisy neighbours.
4 If the money has been stolen, someone must have disabled the alarm system,
because the alarm easily wakes me if it goes off. So the culprit must be a member of
the security firm which installed the alarm.
5 The campaign to eradicate measles has been so successful that many doctors have
never seen an actual case. Ironically, this puts those few people who do contract the
disease in greater danger than they would have been before. The disease can cause
serious complications, and it is difficult to diagnose without previous experience
because the symptoms are similar to those of several other diseases.
(Law School Admission Test, December 1984)
6 There is a much higher incidence of heart attack and death from heart disease
among heavy cigarette smokers than among people who do not smoke. It has been
thought that nicotine was responsible for the development of atherosclerotic disease
in smokers. It now seems that the real culprit is carbon monoxide. In experiments,
animals exposed to carbon monoxide for several months show changes in the arterial
walls that are indistinguishable from atherosclerosis.
(Law School Admission Test, March 1985)
7 Patients on the point of death, who either died shortly afterwards or were revived,
have often reported visions of places of exquisite beauty, intense feelings of peace and
joy, and encounters with loved ones who had predeceased them. These experiences
clearly suggest that there is life after death. Skeptics often claim that such phenomena
are caused by changes in the brain that precede death, because these phenomena
resemble certain altered states of consciousness that can be induced by drugs or
organic brain disease. This objection fails, however, because most of the patients
whose experiences of this nature have been reported were neither drugged nor
suffering from brain disease.
(Law School Admission Test, October 1985)
8 The growth in the urban population of the US has put increasing pressure on
farmers to produce more food. Farmers have responded by adopting labour saving
technology that has resulted in a further displacement of population to cities. As a
result, the farm population, formerly a dominant pressure group in national politics,
has lost political power.
(Law School Admission Test, February 1983)
9 Human beings have the power either to preserve or to destroy wild plant species.
Most of the wonder drugs of the past fifty years have come from wild plants. If those
plants had not existed, medicine could not have progressed as it has, and many
human lives would have been lost. It is therefore important for the future of
medicine that we should preserve wild plant species.
10 Thirty years ago the numbers of British people taking holidays in foreign countries
were very small compared with the large numbers of them travelling abroad for
holidays now. Foreign travel is, and always has been, expensive. So British people
must on average have more money to spend now than they did thirty years ago.
11 Athletes should not be banned from taking performance enhancing drugs. Since they
are allowed to improve their performance through training and coaching, we are
already a long way from rewarding winners simply on the basis of their natural talent.
If these drugs really do improve performance, and if athletes were allowed to take
them, then everyone would improve by the same amount. Thus no-one would have
an unfair advantage as a result of taking drugs.
12 The number of students who get good results in GCSE science examinations is in
decline. To respond to this by making examination questions easier is a big mistake,
because one consequence would be that science teaching in schools would demand
much less intellectual effort from students. If we want to keep Britain at the forefront
of scientific and technological achievement, we must not weaken the scientific
culture of the country.
13 It is clear from the latest figures on women in the work force that women are still
being prevented from getting top jobs due to prejudice against them. Although
women make up 45 per cent of the national work force, and 30 per cent of its
managers, they are barely represented in the very top jobs in law, the police and
business.
14 In a recent study of 210 adults, psychologists assessed the personalities of the subjects
by means of personality tests, and also asked them to list the number of sexual
contacts they had had. The results showed that those who had been judged ‘socially
cold’ had listed more sexual partners than those with other types of personality. Thus
it is evident that people who are socially cold prefer to have a large number of
superficial sexual relationships rather than an emotionally demanding sexual relationship
with just one person.
15 Instead of being locked up, people who commit murder when they are in a psychotic
state should be treated with drugs to change their condition. When in a psychotic
state, they have no control over their own actions. So punishing them is not appropriate
because it cannot make them change their behaviour. Thus locking them up in
prisons or secure units is pointless.