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Crictical Thinking

Arguments; Inferences; The Impact of Additional Evidence; Flaws; Principles; Assumptions.
by

Simon James

on 2 September 2013

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Transcript of Crictical Thinking

Three ways to avoid wrestling with difficult issues:

1. Refuse to think about them.
2. Dogmatism
3. Relativism; who is to say?

Why are each of these a bad idea?
Why Reason?
Critical Thinking is the analytical thinking which underlines all rational discourse and enquiry. As an academic discipline, it is unique in that it explicitly focuses on the process involved in being rational.
Critical Thinking
Are the following arguments?
If so, what's the conclusion?

Pets are good for you. Research has shown that pet owners are less likely than other people to be depressed or to suffer from high blood pressure.
"An argument is a connected series of statements to establish a definite proposition"
You do your thing, I'll do mine.
Estimate the total number of deaths per year in the US (200 million people) from:
Tornado
Fireworks
Asthma
Drowning


There is a lottery in which only 10 tickets are being sold. The prize is £20, the prize will go to one of the 10 ticket-holders, and you are allowed to buy one ticket which will cost you £1. Will you buy this lottery ticket?
Argument Indicators
Reason Indicators
Conclusion Indicators
BECAUSE
IF
SINCE
FIRSTLY, SECONDLY
SO THEREFORE
HENCE THUS
THEN MUST (NOT)
OUGHT (NOT) / SHOULD (NOT)
IN CONSEQUENCE / CONSEQUENTLY
ACCORDINGLY
IN CONCLUSION
Children who are good at spelling usually
have good visual memory. Poor spellers have not
learnt to look at words carefully. Practice in reading does not necessarily help poor spellers.
The presence of security cameras has been shown to reduce crime in areas such as shopping malls. But security cameras are not an unqualified success. Law-abiding citizens do not wish to have all their activities observed, and criminals may commit just as much crime, but do so in areas where there are no cameras.
Tidying up an argument
People on diets lose weight. Jenny has lost weight, so she must be on a diet.
As well as looking for indicator words, it may help to see if the argument can be reordered like so:
Reasons therefore Conclusion
Examples on hand-out.
Then...
Exercise 1, Pg 11 - 13.
Are You Rational?
NB
Conclusions can appear anywhere in the argument.
First identify an argument, then we can evaluate it.
Inferences
We should increase the tax on cigarettes even further. Smoking harms health, meaning smokers are more frequent users of the NHS.
NB Indicates intermediate conclusion
To infer is to come up with a conclusion from the reason(s) presented
A Recent study found that school-age children who participate in school-related sports activities fight less during school and school related activities than do those children who do not participate. It was concluded that sports must satisfy an aggressive impulse which would otherwise be released through fighting.

Which of the following, if true, weakens the conclusion above?
a. School-related activities are always supervised by adults
b. supervisors of school-related sports activities discourage participants from being extremely aggressive.
c. Children who participate in school-related sports activities tend to be more aggressive physically than those who do not participate.
d. approximately 85% of fights children get in to at school take place during break times.
e. Most schools suspend those who fight during school / school related activities from the schools' sports teams
What can you infer in the following?
The pond is frozen this morning. It was not frozen yesterday.
Jane arrived before Jim, although they set off at the same time, and they were both travelling by car
The murder victim died at 9 p.m. on Saturday. It is not yet known whether it was poison or the blow to the head which killed him. The injury to the head would have caused death instantly, had he still been alive when he was hit. It has now been discovered that Ms Brown, the chief suspect, was with friends 5 miles away from the murder scene between 7 pm and 10 pm on Saturday.

If any prisoner can figure out and say to the jailer what colour hat he has on his head all four prisoners go free. If any prisoner suggests an incorrect answer, all four prisoners are executed.
N.B. Being aware of alternative reasoning will help you to decide on the strength of your inference.
Attempt exercise 15, compare answers in small groups.
Additional Evidence
Flaws
The quality of an argument can be altered by additional reasoning or additional evidence.
[Must be judged in relation to the main conclusion]
Nice
conclusion indicator!
Debate:

This house would ban single sex schools

Exercise 10.
In preparing for the debate:

Establish what your conclusion is.

Come up with reasons for believing your conclusion.

Construct your opening argument using reason and conclusion indicator words.

Think about the opposition's case. What information would most weaken their argument?

Think about your case. What information would most weaken your argument? Can you think of rebuttals?
A: One Method of reducing serious crime in the US is to adopt the English system of providing free heroin to heroin addicts.

B. That's absurd. It's just like giving free cars to automobile thieves.

Which of the following, if true, would most strengthen A's argument?

a) Heroin addicts are more likely to be violent under the influence of drugs than when they are anticipating using those drugs.
b) The amount of money needed annually to supply heroin to heroin addicts is less than the amount lost annually by the victims of drug-related crime.
c) It is cheaper to provide addicts with drugs than to jail them after they have committed crimes.
d) The amount of serious crime committed by non-addicts is roughly equal in England and the US.
e) A substantial amount of serious crime is committed by heroin addicts in order to support their habits.
An argument is flawed if it gives no support or weak support for its conclusion. This may be due to flawed logic or an implausible assumption.
Violence on TV:

Some people say that the depiction of violence on television has no effect on viewers' behaviour. However, if what was shown on television did not affect behaviour, television advertising would never influence viewers to buy certain products. But we know that it does. So it cannot be true that television violence does not affect behaviour.
Identifying flaws in arguments
1. Main Conclusion.
Reason: TV Advertising affects viewers' behaviour.
2. Main Reasons and how they are meant to support the conclusion.
3. Does the (main/intermediate) conclusion follow from the reason?
4. Explain why the conclusion does not follow (even if reasons are true). Refer to subject matter, don't just state the name of a fallacy.

Intermediate Conclusion: So, what is shown on TV affects viewers' behaviour.
Main Conclusion: So, violence shown on TV must affect viewers' behaviour.

The fact that some things which are shown on TV affect viewers' behaviour is not a good reason for thinking that violence shown on TV must affect viewers' behaviour.
There have been improvements in the health of the population over the past 30 years, a period during which there has been an increase in the affluence of the country. So the increased affluence of the country has produced the improvements in the health of the population
Reason: Improvements in health have coincided with an increase in wealth.
Assumption (unstated): because the two things occured together, one must have caused the other.
Conclusion: Increased affluence caused improved health.
Flawed because the argument assumes, without producing evidence, that because the increase in wealth occurred during the same period as the improvement in health that it caused it.
Fallacies
Straw Man
The arguer sets up a weakened version of the opponent's position, which is easy to knock down
Ad Hominem
In the ad hominem ("against the person") fallacy, the arguer attacks his or her opponent instead of their argument.
Slippery Slope
The arguer claims that a sort of chain reaction, ending in some dire consequence, will take place; that if we take even one step along the 'slippery slope" we will end up sliding all the way to the end; they assume that we can't stop halfway down the hill.
Post Hoc Ergo Propter Hoc
"Post hoc, ergo propter hoc" translates as "after this, therefore because of this". Assuming that because B comes after A, A caused B is to confuse correlation with causality.
Appeal to Authority
X is true because someone says so.
Ad Populum
If the majority believes that proposition X is true, then it’s presumed to be true.
Begging the Question
"Begging the question" refers to the issue ("question") being debated. In a debate, one may ask for certain points to be conceded in order to speed up the proceedings. To "beg" the question is to ask that the very point at issue be conceded, which is of course illegitimate. It is a circular argument.
Weak Analogy
A is like B.
B has property P.
Therefore, A has property P.
(Where the analogy between A and B is weak.)
Exercise 9.
Bad Science
Principles
A statement with general applicability that sometimes forms the basis of reasoning.

A piece of reasoning may use such a principle without explicitly identifying it as such.

Principles may function in an argument as reasons, as conclusions or as unstated assumptions.
Sometimes, application of a principle to other cases may show that the principle needs to be modified or rejected.
Identify the general principles underlying the following arguments. Are these principles generally applicable?

The United States should abolish the death penalty outright. Capital punishment involves the deliberate taking of human life and all killing is wrong.

‘We should not give high priority to expensive heart treatments for smokers, because they have brought their illness on themselves.’
Killing is wrong.
We should not give high priority to the treatment of self-inflicted illness
Arguments based on principles can be evaluated by applying the principle to other cases, if a principle can form the basis of an unsatisfactory conclusion then the principle will need to be rejected or modified and the original argument is weakened.
Do Exercise 17....
Leviticus 19.28
Ye shall not make any cuttings in your flesh for the dead, nor print any marks upon you: I am the LORD.
Exercise 9. 1-5
Assumptions

A plumber is the father of an electrician’s son. How is this possible?

The electrician is the son’s mother

•Faulty Assumption :
Assuming that the electrician is a man.
Connect all 9 dots using just 4 straight lines
Faulty Assumption :
Straight lines had to be within the confines of the the box of dots.
For the purpose of analysing arguments, we take an assumption (sometimes referred to as presumption) to mean something which is taken for granted, but not stated explicitly.

Assumptions are distinct from reasons or conclusion and may function in the argument as:
In giving support to the basic reasons.
As a missing step/ link in the argument
There are some assumptions which form the whole context in which an argument is presented, so that someone unfamiliar with the context will find it more difficult to understand the argument (ie specialist fields)
Identify the assumption:

The bay is infested with box jellyfish, do not swim there today.
[Box jellyfish are dangerous]
The Negative Test:
The negative test can be used to see if an assumption is required - make the assumption negative, and see if the conclusion of the argument still follows.
The bay is infested with box jellyfish, [box jellyfish are NOT dangerous] do not swim there today.
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