Reasoning Fallacies

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Reasoning Fallacies
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The Process of Hypothesis Testing
Inductive logic/reasoning

• Inspiration
• Case study?

Hypothesis
Test
Results
Theory
Deductive logic/reasoning

• In science, we use reasoning to develop our
  theories. Therefore, it is important that we
  avoid making errors in reasoning.

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Error 1

• Example
• Some of you have objected to the new test
  batteries that were purchased for our program,
  alleging that they have no demonstrable validity,
  were not adequately normed for the kind of
  clients we see, and are unusable for clients who
  are physically disabled. What you have
  conveniently failed to mention, however, is that
  they cost less than a third of the price for the
  other tests we had been using, are much easier to
  learn, and can be administered and scored in less
  than half the time of the tests we used to use.

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Error 1 Red Herrings

• Introducing or focusing on irrelevant information
  to distract from the valid evidence and
  reasoning.
• Its irrelevant whether or not a test is cheaper
  if the data from the test is worthless.
• The Its cheaper argument fails to address the
  opposing argument.

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Error 2

• Example
• The research and reasoning that supposedly
  supports this intervention are a joke. The
  researchers are people who are not
  methodologically sophisticated and there have
  been rumorsI have no idea whether they're true
  or notthat they faked some of the data. The
  advocates of this intervention are the worst kind
  of sloppy thinkers. They are fanatical adherents
  who already have their minds made up they've
  become true believers in their cause. They make
  arguments only a stupid person would accept, and
  mistakes in reasoning that would make an
  undergrad psych major blush. These are not the
  kind of people who deserve to be taken seriously.

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Error 2 Ad Hominem

• Discredit an argument or position by drawing
  attention to characteristics of the person who is
  making the argument or who holds the position.
• Again, this doesnt actually address the issues
  raised in an opposing argument.

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Error 3

• Examples
• In the 6 years that I have been practicing my new
  and improved brand of psychotherapy there has
  not been one published study showing that it
  fails to work or that it has ever harmed a
  patient. It is clearly one of the safest and most
  effective interventions ever devised.
• Since you cannot prove that ghosts do not exist,
  they must exist

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Error 3 Appeal To Ignorance

• There is no (or insufficient) evidence
  establishing that x is false. Therefore x is true.

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Error 4

• Example
• If we pass laws against fully-automatic weapons,
  then it won't be long before we pass laws on all
  weapons, and then we will begin to restrict other
  rights, and finally we will end up living in a
  communist state. Thus, we should not ban
  fully-automatic weapons.

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Error 4 Slippery Slope

• In order to show that a proposition is
  unacceptable, a sequence of increasingly
  unacceptable events is shown to follow from it.

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Mambo 5

• Is a catchy tune, but not what were studying.
• Just seeing whos awake.

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Error 5

• Examples
• My dentist argues that you only need to brush
  your teeth once a week
• Hollywood celebrities do it, you should too

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Error 5 Appeals to (Questionable) Authority

• An appeal to authority is inappropriate if
• the person is not qualified to have an expert
  opinion on the subject
• experts in the field disagree on this issue
• the authority was making a joke, drunk, or
  otherwise not being serious

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Error 6

• Examples
• My friend Wilf is a Newfie and he likes to drink
  a lot, therefore all Newfies must be big
  drinkers.
• I asked six of my friends if they thought
  Vancouver would do a good job hosting the
  Olympics. They all thought we would. Obviously
  Vancouverites have faith in their citys ability
  to host in 2010.

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Error 6 Hasty Generalizations

• The size of the sample is too small to support
  the conclusion
• Very important for scientists to watch out for.
• Must limit your conclusions to what actually
  follows from the data.

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Error 7

• Example
• To see how Canadians will vote in the next
  election we polled a hundred people in Calgary.
  This shows conclusively that the Conservative
  Party will sweep the polls.

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Error 7 Unrepresentative Sample

• The sample used is different than the population
  we want to generalize to
• If you want to generalize to all of Canada, get a
  sample from different parts of Canada

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Error 8

• Examples
• Immigration to Alberta from Ontario increased.
  Soon after, the welfare rolls increased.
  Therefore the increased welfare was caused by the
  increased immigration.

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Error 8 Coincidental Correlation

• (post hoc ergo
• propter hoc )
• It is assumed that because one thing follows
  another that the one thing was caused by the
  other
• Two things occurring in close temporal order do
  nor necessarily have a causal relationship.

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Error 9

• Examples
• An animal is human if and only if it has human
  parents
• Dad is behaving strangely because hes having a
  midlife crisis
• The law must be obeyed, because it is the law.

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Error 9 Circular Definitions

• The definition includes the term being defined as
  a part of the definition

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Error 10

• Examples
• There is no point in raising tuition at UBC
  because it will not fix all the problems
• There is no point in Teachers striking because
  that wont solve the problem with education
• The bargaining process is broken so we
  shouldnt bargain at alljust force them back to
  work.

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Error 10 Searching for Perfect Solutions

• Unless there is a perfect solution to a problem,
  we shouldnt bother trying.
• Similar to essentialism
• Discourages inquiry