Weaknesses in arguments

Causal arguments – post hoc

Causal arguments will attempt to reach a conclusion by assuming that a strong cause is proof.Last year’s summer was the hottest on record. Travel agents are reporting poor sales of foreign holidays this year. People are assuming that this year will be hot too and are going to holiday at home.

Sometimes causes can be very persuasive.The increase in bull bars on jeeps and the increase in deaths of pedestrians in car accidents might be developed into a strong argument but it rests on an assumption.

Exploring Weakness All the great thinkers have one thing in common.

• They all have beards. Therefore their

greatness must be attributable to this fact.

Exploring Weakness Necessary and Sufficient Conditions – some

relationships.

X may have no association with Y – may be coincidence (e.g. bearded greats!)

X is a necessary condition of Y – if X is not present Y cannot occur (e.g. you must be fairly fit to complete a marathon).

X is a sufficient condition for Y – if X is present Y MUST occur (e.g. the heir to the throne is the eldest son of the reigning monarch).

Exploring Weakness

Necessary Conditions – if a necessary

condition for X is not present, then X will not occur (i.e. false)

Sufficient Conditions – if a sufficient

condition for X is present then X must occur (i.e. true)

Exercises Work out if the relationship between X and Y is;

necessary,

sufficient,

neither necessary nor sufficient,

both necessary and sufficient

Exercise necessary,

sufficient,

neither necessary nor sufficient,

both necessary and sufficient

X smoking cigarettes

Y developing lung cancer

Exercise necessary,

sufficient,

neither necessary nor sufficient,

both necessary and sufficient

X driving above the legal alcohol-blood limit

Y being convicted of drunken driving

Exercise necessary,

sufficient,

neither necessary nor sufficient,

both necessary and sufficient

X having 3 A levels

Y getting a place on a degree course at university

Exercise necessary,

sufficient,

neither necessary nor sufficient,

both necessary and sufficient

X Labour winning a large majority of seats in the House of Commons

Y Labour forming a government

Exercise necessary,

sufficient,

neither necessary nor sufficient,

both necessary and sufficient

X having all six numbers in the National Lottery draw on a valid ticket

Y being at least one of the winners of the jackpot

Causes and Consequences A study of Leyland town centre showed that when it

was raining, a lot of people had umbrellas up. Therefore, people putting umbrellas up causes it to rain.

Causes and ConsequencesCigarette advertising on TV was banned 30 years ago.

Since then levels of smoking have fallen. If all smoking adverts were banned the level would fall even more.

Is the conclusion justified by the evidence?

What other explanations exist?

What assumptions must be made to draw this conclusion?

X: Having all six number in a National

Lottery draw on a valid ticket;

Y: being at least one of the winners of a

jackpot prize

Ad hominem – attacking the arguerPeople who demonstrate against the live export of animals say that the trade involves great cruelty. This is clearly not true. These people are just intent on stopping a lawful trade, if necessary by acting illegally and sometimes violently. They can’t have any regard for the law and their behaviour is just like that of a rabble of yobs.

The argument is a criticism of the opposition, not the validity of their point of view.

Straw MenAnti-vivisectionists say that animals should never be used for any type of research. But we need to use animals in developing new and better pet foods: how can we know what foods cats or dogs like best if we’re not allowed to use them in experiments on pet nutrition? It’s obvious that the anti-vivisectionists’ case is fundamentally flawed.

The argument is weakened and then attacked. The case does not tackle the full strength of the opposition’s view.

Slippery Slopes

Where an argument becomes more extreme and less logical as it advances

We all use these!!

There are too many people begging on the streets, and some of them are making a pretty good living at it. If we don’t stop people begging, we’ll soon find that most of the unemployed will start doing it to supplement their benefit. Once the unemployed are doing it in such large numbers, people on low wages will wonder why they should carry on working when so many are just sitting about and getting more money than them. And, once the low paid give up work and begging becomes more and more a way of life for so many, young people won’t bother about getting qualifications and thinking about their careers. They’ll start begging rather than go to school. It won’t be long before begging becomes the main option for a whole generation of young people. Our educational and economic systems will collapse, resulting in a catastrophic national decline. To avert this, we must make begging on our streets a criminal offence punishable by very harsh penalties.

Slippery slopes The argument goes too far and too fast so that the

conclusion ends up a long way from the initial reasoning.

As each point of the argument is developed the case becomes harder to justify.

A single weak link in the chain of thinking and the whole argument falls.

Tu quoque – you too!(also called two wrong don’t make a right)

When Charles Black was accused of driving at 105 mph, and with driving without due care and attention (he was using a mobile phone at the time), he told the court that thousands of people broke the speed limit every day and he was sure that many of them were doing things like adjusting the radio, lighting a cigarette or picking their nose at the time. So, he argued, the case against him should be dropped.

Circular Argument/ Begging the Question.Of all the natural healing methods, homeopathy is the one which is best able to provide a wide range of medicines for all types of disorders. These include digestive orders, muscular problems and allergies. Thus, compared to all other natural healing methods, homeopathy offers the most extensive set of options for any medical condition.

What was the question?!