Identifying Assumptions

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					Identifying Assumptions
Assumptions

What is the meaning of the word assumption?

 In ordinary language the word assumption means
something which is taken for granted but is not stated.

For example, I may assume when I get on an aeroplane
that the pilot ahs been trained and is qualified to fly the
machine safely with me and the other passengers in it. I do
not feel the need to go and ask to see the pilot’s license or
checkup on their history. I am making an assumption. It is
probably a very safe assumption, but it is not based on
conclusive evidence.

.
However in Critical Thinking Paper 1 the word

‘assumption’ means that part of the argument that is

not stated, but is needed in order for the argument to

work i.e. it is another reason that is needed for the
argument to make sense
Assumptions come in two forms:

 Underlying Assumptions or sometimes referred to
as Implicit Assumptions (Paper 1)
                         Or
 Unstated Assumptions or sometimes referred to as
Explicit Assumptions (Paper 2)
In Critical Thinking an underlying assumption works in
two important ways:
• First in giving support to the basic reasons
   presented in the argument
• Second as a missing step within the argument
       perhaps as an additional reason which must be
        added to the stated reasons in order for the
        conclusion to be established or
       perhaps as an intermediate conclusion which
        is supported by the reasons and in turn supports
        the main conclusion.
Therefore an argument rests heavily on the underlying
assumption, as it does the stated reasons, to establish
the conclusion.

Without the underlying assumption the argument will
fail.
Example                               R1
If cigarette advertising were banned, cigarette
manufactures would save the money they would otherwise
have spent on advertising. Thus, in order to compete with
each other, they would reduce the price of cigarettes. So,
banning cigarette advertising would be likely to lead to an
increase in smoking.            MC                   IC
Think about the reasoning.
What conclusion is the author trying to get us to accept?
What basic reason does he offer?
Is there an intermediate conclusion?
Can you identify a stage in the argument which has not
been stated i.e. an underlying assumption/missing
reason?
The argument starts with a basic reason:
If cigarette advertising is banned, cigarette
manufacturers save the money they would otherwise
have spent on advertising.

 and from this draws the intermediate conclusion:
Thus in order to compete with each other, they reduce
the price of cigarettes.

 It then draws the main conclusion:
So banning cigarette advertising leads to an increase
in smoking.
The MC would not follow from the IC if a reduction in the price
of cigarettes made no difference to the numbers of cigarettes
bought and smoked. So an assumption underlies this move
– that if cigarettes were cheaper, smokers would smoke more,
or non-smokers would become smokers. The conclusion does
not say exactly what it means by ‘an increase in smoking’, so
we cannot be sure whether the assumption is

If cigarettes were cheaper, smokers would smoke more,
                             or
If cigarettes were cheaper, more people would smoke.

But it will require one of these assumptions that is underlying
the argument to support the MC.

So the underlying assumption taken together with the IC
gives support to the MC of the argument.
Let’s look at this example:                  C

Advances in fertility treatments will soon allow parents to
choose the sex of their child. This will have serious
consequences for society, as there will be more        R1
unemployed young men and, as most car accidents are
caused by young men, the number of car accidents will
rise.                                       R2


The argument links choice about the sex of a child to
problems related to having more boys than girls. The
argument therefore rests on the idea that parents will
chose boys in preference to girls.
We would say that the assumption is that parents would
choose boys in preference to girls if they are allowed
to choose the sex of their child. You may have realized
this without even thinking about it, but the key point is that
the argument falls to pieces without this assumption.
Example 3            R1                          R2
One third of the population still smokes. Everyone must
know that smoking causes lung cancer and heart disease.
So knowing the dangers of smoking is not sufficient to stop
people from smoking         C
There are two basic reasons here.
Is there a missing step, a missing reason here that is
giving support to the argument?
Yes. The claim that ‘everyone must know…’ suggests that
there is an underlying reason for expecting people to
be well informed on this topic so the assumption made is
that there has been widespread publicity on the
dangers to health of smoking – on television, in
newspapers and by means of posters in the waiting rooms
of doctors, hospitals etc.
So when identifying underlying assumptions
remember that:

An underlying assumption is one that is needed to
support a conclusion or validate an argument.

An underlying assumption is necessary for
accepting the conclusion.
An underlying assumption is a missing
premise/reason.

An underlying assumption is part of the structure of
the argument.

An underlying assumption can be challenged just like
any other premise.
Look at the argument given:

      Ben: Asha’s gone home early.

      Cal: What makes you say that?

      Ben: Her car’s not in the car park.

What is Ben’s argument?
Ben’s argument is that Asha has gone home early.
The reason he gives is that her car is not in the car park.
Is there anything extra that Ben is assuming when he
draws his conclusion?
He is assuming a lot.
 He is assuming that Asha has not gone somewhere
other than home.
 He is assuming that no one else drove the car out of the
car park.
 Yet another assumption he is making is that she came in
her car that day.

All of these assumptions Ben makes are unstated
assumptions or explicit assumptions. They are not
needed to come to the conclusion that Asha has gone
home early.
What is needed to come to the conclusion and to accept
the argument that Ben makes, is to make the assumption
that Asha herself took the car home. Accepting that Asha
drove the car herself is therefore necessary to the
argument which fails completely without it.

That is why it is called an underlying assumption.
    R1           R2        R3
                                          R4(IC)
Young people are not very interested in politics and tend
not to vote. Most people who do vote are the older, well-off
people. Governments tend to represent the interests of
those who have voted for them. Elected governments,
therefore, do not represent all sections of society.
Politicians should change their approach to ensure that
more young people vote.       MC


This argument rests on the idea that governments should
represent all sections of society.

In other words, the argument relies on an assumption that
governments should represent all sections of society.
This example again shows clearly that an assumption is
part of the structure of an argument. To be more
precise: assumptions are a missing step in the argument,
a missing reason that the argument needs in order to
support the conclusion. It is the missing reason between
the other reasons and the conclusion.

You can see this more clearly if we write the assumption
into the argument as follows:
R1 Young people are not very interested in politics and
tend not to vote.
R2 Most people who do vote are older, well-off people.
R3 Governments tend to represent the interests of those
who have voted for them.
R4(IC) Elected governments, therefore, do not represent all
sections of society.
R5(U Assumption) Governments should represent all
sections of society.
MC: Politicians should change their approach to ensure
that more young people vote.

The underlying assumption now acts as the fifth reason
in the argument.
         R1                                    R2
Recent research has shown that a foetus can hear at 30
weeks old. Computer-generated white noise was played to
foetuses between 23 and 34 weeks old. Ultrasound
scanning did not pick up any response under 30 weeks old
but it did detect heart and movement responses in the 30-
34-week-olds. This fits with the fact that a baby’s hearing
                                                          R3(IC)
develops in the 30-34 week period. Given this new
knowledge, we should encourage pregnant women to play
music to their babies. MC
Which of the following is an underlying assumption of the
    above argument?

A.   Heart and movement responses cannot be detected in
     foetuses under 30 weeks old.
B.   Foetuses over 30 weeks old can distinguish between
     different types of sound.
C.   Foetuses are particularly responsive to computer-
     generated white noise.
D.   Hearing sounds such as music is beneficial to a foetus
     of at least 30 weeks old.
A. Heart and movement responses cannot be detected in
foetuses under 30 weeks old.



It is not A. This statement is not in the passage, in that we
know that we can detect movement in the 30-34-week-old
foetuses but not what the results were below this age.
However, even if this statement were true, it would tell us
nothing about whether or not we should encourage women
to play music to their babies. It is a statement that is not in
the passage, but it is not a missing step in the argument.
B. Foetuses over 30 weeks old can distinguish between
different types of sound.



It is not B. The argument is about sound in general;
whether particular types of sound can be detected does not
really mater. All we need to know is that babies can hear.
And we are told this in the passage – their hearing
develops at 30-34 weeks. This statement therefore, is not
an assumption either.
C. Foetuses are particularly responsive to computer-
generated white noise

It is not C. This is a bit like A, in that it may be true or not
and is certainly not in the original passage. However, the
conclusion is about playing music to babies in the womb,
so again we have a statement that is not in the original
passage, but is not needed for the argument to work, which
means it is not an assumption.
D. Hearing sounds such as music is beneficial to a foetus
of at least 30 weeks old.



D is the correct answer. By stating that there is a benefit to
foetuses we suddenly are given a reason why pregnant
women should play music to their unborn babies. This is
the missing step in the argument – in other words the
underlying assumption that is needed to make the
argument.
Many people today think that museums should be like R1
private companies, concentrating only on activities which
are profitable. In this way, it is seen as acceptable for
museums to ignore the unfashionable or less popular parts
of our history. The proper function of museums, however, is
to provide a balanced picture of our history. Therefore weR2
must ensure that they are subsidized by the state rather
than having to worry about being profitable.         C
.
Which one of the following is an underlying assumption
    of the above argument?

A.   Museums cannot be run like private companies.
B.   The government is prepared to subsidies museums.
C.   Only museums can provide a balanced picture of our
     history.
D.   Museums cannot provide a balanced history without
     state subsidy.
E.   Museums which give a balanced picture of our history
     are more likely to be profitable.
A.Museums cannot be run like private companies.



A is not assumed. The passage does not suggest that
museums cannot be run like private companies but that
they should not be run in that way for the reasons given. If
they could not be run like private companies there would
not be no need to ensure that they were not. A would be a
very odd assumption to make and therefore can be safely
ruled out.
B. The government is prepared to subsidies museums.



B is not assumed either. The argument is trying to show
that the government should subsidize museums. It does
not take for granted that the government is prepared to
subsidize them. You can argue that the government ought
to do something even if you know they have no wish or
intention to doe so.
C. Only museums can provide a balanced picture of our
history



C is nor assumed. There could be many other institutions –
publishers, libraries, universities and so on – that could
provide balanced histories. Museums are not the only
possible providers.
E. Museums which give a balanced picture of our history
are more likely to be profitable.

E is not assumed. The author contrasts museums that
simply concentrate on being profitable with museums
carrying out their main function of providing a balanced
picture of our history. If anything, the author sees museums
that provide a balanced picture of our history as less likely
to be profitable. E therefore contradicts the other premises
rather than underlying them. No claim that contradicts a
main premise could also be an underlying assumption.
In the days before the arrival of the Internet, publishers
and booksellers effectively controlled what people read,
since very few would-be authors could afford the high
financial risks of publishing themselves. The Internet has
changed all that. Now anyone can express views publicly,
or distribute information, at little or no cost. Those who
are fearful of the Internet should therefore stop dwelling
on its faults, and acknowledge that its continued growth
is, on balance, in the public interest, not against it. For,
almost at a stroke, it has given us freedom of information
on a scale that could never previously have been
                                                   MC
imagined.              R1

                             IC (R2
Which of the following is the underlying assumption?

A.   There is no reason for anyone to be fearful of the
     internet
B.    Freedom of information is in the public interest.
C.    In the past publishers and booksellers told authors
     what to write.
D.   The internet will continue to grow
E.    Everyone has the right to express any opinion.
The step from the intermediate conclusion to the main
conclusion works only if we assume that freedom of
information is itself in the public interest, since that is the
sole reason given for saying that the Internet benefits the
public. If it could be shown that on balance freedom of
information was not in the public interest – i.e. that it did
more harm than good – then the argument would be fatally
damaged.

B is the one that expresses this assumption. It states
plainly ‘Freedom of information is in the public interest.’
none of the other claims is required for the argument to
succeed.
A does not have to be assumed; there could be reasons to
be wary of the Internet whilst still concluding that on
balance it was a good thing.


C Is not necessary for the argument. We are told that
publishers, booksellers etc. may have controlled what was
read by deciding to print this or sell that; but that is not the
same as telling authors what to write.
D does not have to be assumed either. The argument is
about whether the Internet is good for people, not how long
it will last. It does not really even imply that it will last,
though it is plainly the author’s hope that it will.

E cannot be assumed. It is beyond the scope of the
argument, which claims only that the Internet gives people
the ability to express their own opinions this does not imply
that they have a right to express any opinion, as E claims.
The Internet has brought many advantages. It is a C
wonderful source of knowledge and, used intelligently, it
provides for a healthy exchange of views. But history will
prove that the Internet is a far greater force for harm than R1
for good. Its great flaw is that the information on it is not,
and indeed cannot be, regulated. Anyone can access it and
anything can be published on it, freely and at little or no
cost.                                                      R2


What is the key assumption underlying this argument?


   It has to be assumed that unregulated exchange of
                    information is bad
Homework Assignment

Read
Critical Thinking – John Butterworth.
Chapter 9 - Assumptions

				
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