Logical fallacies
When constructing or analysing an argument it is important to examine any errors in logic related to the claim.
Source of the information
Some arguments rely on analysing the source of other information. While it is important to consider the source, the specific claims and evidence should also be examined.
This argument involves attacking the person making the claim instead of addressing the claim itself.
Example: "Johnson (2006) does not have a PhD in nuclear physics, so his argument must be incorrect."
This argument suggests that an idea is correct because many people believe it is true, or because it has been popular or traditional.
Example: "Slavery has always been legal, therefore it must be moral."
This argument uses the authority of the source as proof of the validity of the argument.
Example: "O'Neill (2006) has been a film critic for forty years, and calls Jaws the greatest film ever made, so Jaws is the greatest film ever made."
Connection between claim and evidence
The most crucial part of an argument is the link between the proof (the evidence) and the assertion being made (the claim). Some arguments fail because this link is imperfect.
This argument suggests that because two events happen at the same time, or one after the other, they must be related.
Example: "Crime increased following the Rainbow Warrior bombing, so the bombing must have caused an increase in crime."
This type of argument assumes too much or too little based on the evidence.
Example: "The weather forecast said it would rain today, and it did, so the weather forecast is always correct."
An appeal to ignorance is when lack of evidence is seen as proof for the opposite position.
Example: "No-one saw Amelia Earhart die, so she must still be alive."
Consideration of other evidence
No piece of evidence exists in a vacuum - it is all a part of a larger body of evidence. When making an argument, it is important to consider the 'big picture'.
Concentrating on evidence that supports the argument while ignoring evidence that disagrees.
Example: "The results from experiments 1 and 2 show that the mean is the same as that predicted, which confirms the hypothesis; experiments 3 and 4 produced data not consistent with this, so they should be disregarded."
Considering only the extremes of the argument and ignoring other alternatives, such as a more reasonable approach in the middle.
Example: "In order to be successful in business you either have to focus on customer satisfaction or employee satisfaction."
Misrepresenting a counter-argument and then arguing against that weaker form instead of paying attention to the strongest counter-argument.
Example: "Taxes should be raised. Those who want taxes kept low want unemployed people to starve."
A statement that has some truth, but doesn't tell the whole story and can therefore lead to false conclusions.
Example: "Fat is bad for you, so you shouldn't eat any fat."