Critical Thinking - Flaws

Definitions for argument flaws you will need to know for AS Critical Thinking with OCR (new spec. 2009)

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Straw Man

A straw man argument or flaw occurs when an arguer 'misses the point', distorts or exaggerates of an opposing argument. This may be done on purpose to make it easier to write a counter argument or it may be because the original argument was poorly written. For example:

Person A: I am for the war in Iraq as it has given Iraqis more freedom

Person B: Person A is in favour of our troops killing innocent Iraqi children and abusing children, this is wrong, therefore the war on Iraq is wrong.

Here Person B is guilty of a straw man argument by misrepresenting what was actually said by Person A in order to make it easier to create a counter argument.

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Necessary and Sufficient Conditions

A necessary condition is a condition which must be true in order for an event to happen. A sufficient condition is an condition which, if true, guarantees an event will happen.

By confusing necessary and sufficient conditions an argument is flawed. For example:

To buy drinks you need to be 18, Harry is 18 therefore he will buy drinks for us.

Here being 18 is necessary condition which needs to be met for Harry to buy drinks. It is however not sufficient to buy drinks, Harry will need money and be thirsty (amongst many other things!). Another example:

Radiation causes cancer, Kevin has cancer, therefore he was exposed to radiation.

In this example exposure to radiation is a sufficient condition to cause cancer, that is if it is true (i.e. Kevin has been exposed to radiation) then Kevin will get cancer. The flaw in the argument is that exposure to radiation is not a necessary condition to cause cancer, it can caused by other things such as asbestos.

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Ad hominem (Attacking the arguer)

Attacking the arguer is a very straight forward flaw. If an argument attacks an opposing view by attacking the person putting it forward rather than the reasons in the opposing argument then the argument is flawed. This is also known by the Latin phrase 'ad hominem' meaning 'argument against the man'. Attacking the arguer is not a good reason to accept an argument. For example:

Rachel is blonde and so doesn't know what she is talking about; therefore her views on abortion shouldn't be accepted.

Clearly the colour of Rachel's hair has no relevance on her argument on abortion.

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A circular argument uses a conclusion as one of its reasons so the argument goes around in circles getting nowhere. For example:

Your hair is brown because you have brown hair.

The problem with this argument is that if you believe the reason then you must already believe the conclusion rendering the argument pointless. On the other hand if you don't believe the conclusion then you cannot believe the reasons given to support it. Either way the end result is you believing what you started with.

Begging the question is a special type of circular argument where the reasons can only work if the conclusion is assumed to be true. For example:

You can trust me, I wouldn't lie to you.

To believe the reason, "I wouldn't lie to you" you must accept the conclusion, "You can trust me".

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Mistaking cause and effect

The flaw of causation or 'correlation not causation' flaw is committed by reasoning that because two events happen together there is a direct link between the two. In simple terms:

A happened before B, therefore A caused B.

The flaw here is not considering any other reasons or explanations for the two events happening together, it could something else, C, causes both A and B. The simple fact that there is a correlation between two things does not imply causation.

Post hoc is reasoning one thing to be the cause of something another, simply because it occurs before it.

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Slippery slope

One thing leads to another, setting off a chain of events or actions from a single original event. A slippery slope flaw reasons that because the 'last link' in such as a chain is bad so is the original event. If the original event could possibly lead to the last event then this reasoning is not fallacious, the flaw occurs when the original event is not properly linked to the last event by making extreme and unjustified jumps. For example:

You should do some revision, if you do not get a B in your A level exams you won't be able to go to University and so won't be able to get a job and die a homeless man.

Here the links between events are far too extreme to be valid, not getting a B may stop you from going to your university of choice however to jump from this to not being able to get a job is unjustified.

Slippery slopes aren't always negative, turning the above exam around:

You should do some revision, if you get a B in your A level exams you'll be able to go to University and get a job paying £100,000 and die a millionaire.

This argument is as bad as previous, even if the last link in the chain is seen to be 'good'.

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Reasoning from wrong actions

Reasoning from wrong actions uses a wrong action to justify another wrong action. There are two forms of this type of flaw.

Two wrongs don't make a right

A "two wrongs don't make a right" flaw justifies a bad action on the basis another bad, but different, action is accepted. For example:

James isn't doing his work in class therefore I can text in class.

Here James' wrong action doesn't justify your wrong action.

Tu quoque

Tu quoque means 'You too' in Latin. It is an attempt to justify a wrong action on the basis that someone or everyone else does it too. For example:

It doesn't matter that I speed, everyone else does it.

Everyone else's wrong actions are not a valid reason for you to do the same wrong thing.

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False dichotomy (Restricting the options)

This type of flaw is often also called a 'false dilemma'. It is an attempt to justify an action or conclusion by making it seem as though there aren't any other options. For example:

The big bang theory must be true, the only other option is some sort of super being 'creator' which is unlikely.

This argument ignores any other theories for the creation of the universe.

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A generalisation uses a specific case or specific evidence to support a general conclusion. For example:

I saw video footage of a police officer hitting a member of the public, therefore all police are thugs.

Here the flaw is quite obvious; we simply cannot use such a specific case about a single police officer to draw a conclusion about all police officers.

A generalisation may also be 'sweeping', which involves drawing a conclusion of all from many. For example:

Most men like football, therefore all men like football.

Again the flaw here is obvious, we cannot move from many to all.

Generalisations are often the result of stereotypes and prejudice.

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Fantastic, thanks!

Jake Small


Thanks alot this has been a big help :)



Thank You they are really helpful :D

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