Identifying Assumptions

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Identifying Assumptions
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• 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 pilots 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.
• .

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• 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

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• 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)

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• 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.

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• 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.

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• Example
• 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.
• 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?

R1



MC
IC
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• 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.

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• 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.

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C

• Lets look at this example
• 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 unemployed young men and, as
  most car accidents are caused by young men, the
  number of car accidents will rise.
• 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.

R1
R2
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• Example 3
• 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
• 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.

R1
R2
C
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• 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.

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• 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.

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• Look at the argument given
• Ben Ashas gone home early.
• Cal What makes you say that?
• Ben Her cars not in the car park.
• What is Bens argument?
• Bens argument is that Asha has gone home early.
• The reason he gives is that her car is not in the
  car park.

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• 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.

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• 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.

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R1
R2
R3

• 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.
• 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.

R4(IC)
MC
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• 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

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• 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.

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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
  babys hearing
• develops in the 30-34 week period. Given this new
• knowledge, we should encourage pregnant women to
  play
• music to their babies.

R3(IC)
MC
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• Which of the following is an underlying
  assumption of the above argument?
• Heart and movement responses cannot be detected
  in foetuses under 30 weeks old.
• Foetuses over 30 weeks old can distinguish
  between different types of sound.
• Foetuses are particularly responsive to
  computer-generated white noise.
• Hearing sounds such as music is beneficial to a
  foetus of at least 30 weeks old.

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• 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.

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• 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.

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• 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.

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• 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.

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• Many people today think that museums should be
  like 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 we must ensure that they are subsidized
  by the state rather than having to worry about
  being profitable.
• .

R1
R2
C
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• Which one of the following is an underlying
  assumption of the above argument?
• Museums cannot be run like private companies.
• The government is prepared to subsidies museums.
• Only museums can provide a balanced picture of
  our history.
• Museums cannot provide a balanced history without
  state subsidy.
• Museums which give a balanced picture of our
  history are more likely to be profitable.

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• 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.

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• 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.

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• 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.

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• 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.

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• 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 imagined.

MC
R1
IC (R2
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• Which of the following is the underlying
  assumption?
• There is no reason for anyone to be fearful of
  the internet
• Freedom of information is in the public
  interest.
• In the past publishers and booksellers told
  authors what to write.
• The internet will continue to grow
• Everyone has the right to express any opinion.

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• 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.

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• 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.

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• 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 authors 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.

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• The Internet has brought many advantages. It is a
  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 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.

C
R1
R2

What is the key assumption underlying this
argument?
It has to be assumed that unregulated exchange
of information is bad
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• Homework Assignment
• Read
• Critical Thinking John Butterworth.
• Chapter 9 - Assumptions