Critical Thinking
Critical Thinking
1) Understanding the nature of
arguments
2) Reliable and unreliable arguments
Critical Thinking
We all argue but how well do we
do it? Are the arguments ‘sound’
or merely opinions with little
factual basis?
Critical Thinking
Look at the following four
arguments.
Which of these are well
structured?
Critical Thinking
We had to go to war, because:
If Saddam Hussein had gained chemical weapons he
either would have used them or made them
available to terrorist organisations.
Saddam Hussein was developing such weapons.
We could not allow him to gain such weapons.
Therefore, we had to prevent him from doing so, either
by peaceful means or by going to war.
We could not do it by peaceful means.
Critical Thinking
Those who would allow Saddam to
develop horrendous weapons in light
of his previous use of chemical
weapons against the Kurds are naïve
pacifists. War is a necessary evil – we
cannot let madmen do what they want
just because we do not want to get our
hands dirty. Remember what happened
in 1939!!
Critical Thinking
Blair is just Bush’s poodle, and GWB
was just out to finish his dad’s work.
It’s all about American imperialism
and the desire for control of oil.
Anyone who thinks that war is ever a
good idea is playing into the hands of
the American military-industrial
complex.
Critical Thinking
By going to war, the coalition was able to
oust Saddam Hussein.
Ousting Saddam Hussein was a good thing.
However, by going to war, it is likely that the
entire Middle East will be further
destabilised, fundamentalism will grow, and
religious intolerance will increase.
These consequences outweigh the benefits of
ousting Saddam Hussein.
Therefore, we should not have gone to war.
Critical Thinking
There are three main reasons for
developing our critical skills.
They are…
Critical Thinking
1) Avoid being led into error by
others.
2) Develop skills that will increase
our skills of persuasion.
3) The pursuit of truth.
The Wason & Johnson-Laird Test
Exercise 1 (p.5)
How do we solve this problem?
The Wason & Johnson-Laird Test
Don’t worry if you got it wrong or
didn’t know. In the original test,
only 5 out of 128 USA college
students got it right. By the end of
the unit you will know the
answer.
The ‘Conjunction Fallacy’.
Jacob is a 35 year old exphilosophy student who is
politically active and highly
intelligent. While at university, he
was very active in the animal
rights movement. Which is more
likely?
The ‘Conjunction Fallacy’.
1) Jacob is a computer
programmer for a large
multinational company.
2) Jacob is a computer
programmer for a large
multinational company and a
vegetarian.
(85% will get it wrong).
1) The purpose of an argument
Philosophy is about being able to
evaluate the arguments for and
against beliefs i.e. the existence of
God or the killing of animals. If we
cannot do this we will never be able
to put across good arguments.
Purpose of argument
We need to be able to
1) Provide others with good reasons
to accept a claim you believe to
be true.
2) Evaluate whether there are good
reasons to accept/reject claims put
forward by others.
Purpose of argument
Philosophy is as much concerned
with why we might believe
something as it is with what it is
we believe.
Look at the following discussion
Purpose of argument
John: it is wrong to kill animals, even
to eat them.
Kevin: no it isn’t. There’s nothing
wrong with eating them, hunting
them or using them for sport.
John: That’s rubbish.
Kevin: Watch it or I’ll give you a
slap.
Purpose of argument
This is an important area in
philosophy: morality or what should
be or could be.
However, it is a bad argument.
But why?
Look at this argument
The purpose of argument
Lucy: There is never any good reason
to kill animals.
Mira: Not true. Sometimes humans
need to kill animals in order to
survive. Animals sometimes attack
people and sometimes we have to kill
them for food.
Purpose of argument
Lucy: Maybe: but you are assuming
that human life is more valuable than
the lives of animals. All life is equally
important.
Mira: Human life is more valuable
because we are more developed than
animals. We suffer more, think more
and feel more.
Purpose of argument
Did you notice the differences?
Instead of just stating a view they
start to offer reasons for their beliefs.
They also start to engage with the
claims made by the other and respond
to it. This is philosophical thinking.
Purpose of argument
Critical Thinking involves the study
of ‘arguments’ and not shouting
matches or fights.
So what is a good argument?
Spotting arguments
Exercise 2 (p.8)
Which of the following do you think
contain arguments? For each passage,
try to explain the answer you gave
2) The distinction between
arguments and statements
a) Statements
Arguments are made up from
statements (claims, propositions).
When someone makes a statement
they assert that something is the
case.
2) The distinction between
arguments and statements
a) Statements
Statements, are therefore, true or
false.
Here are some statements:
2) The distinction between
arguments and statements
a) Statements
Snow is white
The sky is blue
Edinburgh is the capital of Wales
Bolivia is larger than Argentina
God exists
Celtic are the best team in the world
2) The distinction between
arguments and statements
There are many statements which we
cannot tell if they are true or not
i.e. ‘there is life on at least three
planets in distant galaxies’. This
is either true or false but how can
we tell? Let’s look at other
language.
2) The distinction between
arguments and statements
Assertions or statements – the door is open.
Commands or imperatives – open the door.
Questions – who is the tallest in the room?
Expressions of emotion – Mmm, lovely
2) The distinction between
arguments and statements
Commands, questions and expressions of
emotion or feeling are not statements
because they cannot be true or false.
In order for a sentence to be a statement it
must be true or false. We need to be
able to recognise this.
Exercise 3
(page 10)
2) The distinction between
arguments and statements
b) Arguments
Arguments must have reasons to
support them. Think back to the
argument between Lucy and Mira
(p. 7). Both give reasons for their
beliefs.
2) The distinction between
arguments and statements
b) Arguments
All of Mira’s claims are statements. We can
think of an argument as a list of
statements linked together. The point
of this is to produce a conclusion that
will be true. An argument is designed
to prove the truth of a particular claim.
Here are some examples of arguments.
2) The distinction between
arguments and statements
b) Arguments
(p.11)
2) The distinction between
arguments and statements
b) Arguments
These are arguments because they are
attempting to prove that a
statement is true or false.
The statement after the word
‘therefore’ is the conclusion of the
argument.
2) The distinction between
arguments and statements
b) Arguments
To prove some claim, is to
demonstrate why it must be true,
given that other things are true.
Let’s think about Alice again.
2) The distinction between
arguments and statements
b) Arguments
All humans are mortal (true)
Alice is human (true)
Therefore, Alice is mortal (true)
The conclusion is true because the
statements are true.
2) The distinction between
arguments and statements
b) Arguments
The major difference between
statements and arguments are:
Statements are asserted
Arguments offer proof in their
conclusions
2) The distinction between
arguments and statements
b) Arguments
If we reject the truth of a statement
we deny it
If we offer an argument against it is
an attempt to refute it.
Look at the following example
2) The distinction between
arguments and statements
b) Arguments
‘Smoking is good for your health’. To
say ‘No, it’s not’ would be to
deny the statement. If someone
said ‘No it’s not – smoking causes
cancer, which can kill you’ they
would be attempting to refute it.
2) The distinction between
arguments and statements
b) Arguments
When we reach a conclusion based on
other claims that feature in the proof,
we are said to infer (deduce or draw)
the conclusion. ‘I infer from the fact
that Alice is human and the fact that all
humans are mortal, that Alice is
mortal’.
2) The distinction between
arguments and statements
b) Arguments
‘Infer’ does not mean ‘imply’. To
imply something is to hint at or
suggest it. This is a common
mistake, but a serious mistake
nevertheless.
Exercise 4 (page 12)
3) Argument structure
As we have seen, the conclusion of an
argument is the claim an argument seeks to
prove.
Statements used in the argument in support of
the conclusion are known as premises.
Lets look again at an example. (page 12)
3) Argument structure
The writer is trying to convince his audience
that it is Saturday – this is the conclusion
of the argument. The writer does this in 2
ways
a) If Doctor Who is on the TV, it must be
Saturday
b) Doctor Who is on TV.
c) These are the premises of the argument.
3) Argument structure
Arguments can have any number of premises
The premises need not be true.
A false premise (Edinburgh is in Wales) doesn’t
mean it’s not an argument because the
conclusion can still be true (p. 12).
It would be tempting to think that good arguments
will be those with true premises and a true
conclusion but this is not always the case. Look
at the following:
3) Argument structure
Grass is green (premise)
Snow is white (premise)
Therefore,
all dogs are mammals (conclusion)
This includes two premises and a conclusion,
so by the above definition it should count
as a good argument – but it clearly isn’t.
Why?
3) Argument structure
1) Hidden or Implicit premises
Some premises remain unstated in everyday
arguments – usually because everyone accepts
them.
‘I think murderers should be hanged. That way they
will not be able to commit murder again, and the
existence of capital punishment will deter others
from taking life from another human being’.
3) Argument structure
1) Hidden or Implicit premises
What is the hidden or implicit premise?
If you are dead, you cannot kill.
Not if you live in Buffy the Vampire Slayers
world, or Resident Evil
The point is, that unless we state hidden or
implicit premises, we will be unable to
fully evaluate the argument in question.
3) Argument structure
So, grass is green (true)
Snow is white (true)
Therefore, all dogs are mammals (true)
These premises do not give us any reason or
justification to believe the conclusion is
true.
3) Argument structure
The structure or form of the argument is very
important as this provides the truth of the
premises and the truth of the conclusion.
Lets look at an example. (page 14)
3) Argument structure
(p1) If I work hard, then I will pass my exam
(p2) I did work hard
Therefore
(c) I will pass the exam
Look at Para 4 & 5 on page 14
3) Argument structure
It is very easy to identify the premises and the
conclusions of the examples we have
looked at so far. But in everyday life this
is not always the case.
Let’s look at 2 examples. (pages 14 & 15)
3) Argument structure
See if you can spot:
The premises
The conclusion
The implicit premises
The structure/form of the argument
3) Argument structure
‘Freedom of speech is more important to
society than the offence certain books
might cause to individuals. People can be
offended by anything, from nudity and
bad language to trivial things, such as a
person’s choice of clothes or haircut. This
shows that we should not ban books
solely because they cause offence’.
3) Argument structure
‘A baby is a lovely little gift from above. Who
would ever want to refuse a gift,
especially one from such a glorious
benefactor? If something is a gift from
above, then it should not be refused.
That’s why contraception should be
banned. It would be like refusing a lottery
win or a free two-week holiday abroad’.
3) Argument structure
Conclusions can appear at the end, in the
middle or at the beginning.
We must be able to identify it where ever it
appears.
In the first example, ‘this shows us that’ leads
us to see that the statement following this
‘we should not ban books solely because
they cause offence’ is the conclusion.
3) Argument structure
Other phrases that can help might be:
‘therefore’, ‘thus’, ‘this demonstrates that’ or
‘we can conclude’.
And although this does not work every time it
will help us establish the claims within the
argument through their connections.
3a) ‘If…then...’Conditional
statements
‘If and then’.
By asserting that ‘if’ (something-or-other) is
true (or happens), ‘then’ (something else)
will also be true (or will happen), the
speaker is drawing a link between the two
things. (p.12 (B) & (D))
Some examples (page 16)
3) Argument structure
•
•
•
•
•
•
•
If 2+2=4, then 4-2=2.
If the Conservative Party wins the election, then
Tony Blair will not be PM.
If Edinburgh is in Scotland, then it is in Britain.
If I let go of this pen, it will fall to the floor.
If I steal that book, then I will have committed a
crime.
If I go to visit my granny, I will not be going to
the cinema.
If I am dreaming, then this is not real.
3) Argument structure
What is being claimed here?
There is a direct connection between
the two statements, namely that if the
first statement is true, then so is the
second.
‘If I let go of this pen, it will fall to
the floor’.
3a) Conditional statements
• If…then… statements are known as
conditional statements because the truth of
the second claim is conditional on the truth
of the first.
• I didn’t pass the exam (p2)
• If I had worked hard, then I would have
passed the exam (p1)
3a) Conditional statements
• The statement on which the connection is
conditional – the one introduced by ‘if’ is
called
• The antecedent
3a) Conditional statements
• The other – coming after ‘then’ is called
• The consequent
3a) Conditional statements
• When the first statement is true, so is the
second. So…
• If 2+2=4 it is also true that 4–2=2
• There is no suggestion that the first causes
the second or makes it true: the claim is that
if the antecedent is true, then, so is the
consequent.
• All conditional statements have this form.
3a) Conditional statements
Conditionals often feature in arguments such
as (B) p. 12.
(p1) If Dr. Who is on TV, it must be Saturday
(p2) Dr. Who is on TV
Therefore
(c) It must be Saturday
3a) Conditional statements
There are two premises in this argument
Given the first premise, we need the second
premise, in order to have the right to infer
the conclusion
Sometimes the ‘then’ is left unstated and we
need to look out for this
3a) Conditional statements
Do conditionals tell us anything else?
Assume that (p1) is true – ‘if Dr. Who is on
TV, it must be Saturday’. But…
What if you are told it is not Saturday?
(Forget that it could be a repeat or on Sky).
What can we infer from this?
3a) Conditional statements
Exercise 5 – Conditional statements 1
(page 17)
3a) Conditional statements
There are two legitimate conclusions that we can
draw based upon a conditional statement.
If we know the conditional and know that the
antecedent is true, then we can infer the
consequent
(p1) If Dr. Who is on TV, it must be Saturday
(p2) Dr. Who is on TV
Therefore
(c) It must be Saturday - BUT
3a) Conditional statements
If we know the conditional and know that the
consequence is false, then we can infer that the
antecedent is also false
(p1) If Dr. Who is on the TV, it must be Saturday
(p2) It is not Saturday
Therefore
(c) It is not the case that Dr. Who is on TV
3a) Conditional statements
If we know the conditional and know that the consequent is
true, does this tell us anything?
(p1) If Dr. Who is on TV, it must be Saturday
(p2) It is Saturday
(c) Dr. Who is on TV
N0,NO,NO,NO
But Why?
3b) ‘Or’ statements
‘Or’ is often used with ‘either’
• The baby will be male or it will be female.
• Either John will win the election or David will.
• You can have the chocolate or the cake.
• I will go to the cinema or the concert.
• To gain entry to the college, you need three Bs
or two As.
• I will become a teacher or a social worker.
3b) ‘Or’ statements
Such statements have an important place to play
within critical thinking. Just as with
conditionals, this is because they serve to
connect the truth of two statements, although in
a very different way from ‘if… then…’. Rather
than saying that the second statement is true if
the first is, ‘or’ statements claim that at least one
of the statements is true. So the following are
true:
3b) ‘Or’ statements
•
•
•
•
•
Either the Allies won the war in Europe or
Germany and Italy did.
Either Tony Blair won the election or Michael
Howard did.
Killing is always wrong or it is not always
wrong.
Lee Harvey Oswald shot John Fitzgerald
Kennedy or someone else did.
You can get into university with three Bs or you
can get into university with 2 As.
3b) ‘Or’ statements
In critical thinking or
connects two
statements:
I will get Mr. Fyfe for
philosophy or I will get
Mr Cassie
3b) ‘Or’ statements
•
These are not true
•
The moon is made of cheese or it is made of
glass.
Edinburgh is in Germany or it is in France.
Killing is always acceptable or theft is always
acceptable.
•
•
3b) ‘Or’ statements
•
But we have to be careful of ‘or’ in arguments
•
(page 20)
3b) ‘Or’ statements
•
Exercise ‘Or’ statements
•
(page 21)
3c) ‘And’ statements
•
•
•
These statements are also known as
conjunctions
They are used to join two statements
(try to explain why!)
Statements joined by ‘and’ are called
conjuncts
3c) ‘And’ statements
•
Some examples (p22)
Grass is green and snow is white.
Grass is green and snow is purple.
2+2=5 and 3-1=3.
Ask yourself: which of these are true?
3c) ‘And’ statements
It seems that only the first of these
sentences is true – why?
It is the only example that has two true
statements joined by ‘and’.
An ‘and’ statement can only be true when it
contains two true statements
3d) ‘all’ and ‘some’
• The fourth group of statements we will
consider here are those using the words ‘all’
and ‘some’. These words are called
quantifiers, as they are used to discuss
quantities – more than one example – of a
particular kind of thing: all dancers are fit;
some animals lay eggs; some Scots can
speak Spanish; all Spaniards can speak
Spanish
3d) ‘all’ and ‘some’
• Exercise p. 23 & 24
3d) ‘all’ and ‘some’
• Exercise p.27 & 28
4. Recognising everyday arguments
• A baby is a lovely little gift from above.
Who would ever want to refuse a gift,
especially one from so glorious a
benefactor? If something is a gift from
above, then it should not be refused. That’s
why contraception should be banned. It
would be like refusing a lottery win or a
free two-week holiday abroad!
4. Recognising everyday arguments
• Exercise p.29 & 30
• Conclusions for
everyday arguments