Logical Fallacies

This is a brief description of many of the logical fallicies that exist. It is taken from Stephen Downes (http://www.datanation.com/fallacies/index.htm). Unfortunately the link has since been deactivated. If you want more information, please use refer to a textbook or search on the internet.

Fallacies of Distraction

  • False Dilemma: two choices are given when in fact there are three options
  • From Ignorance: because something is not known to be true, it is assumed to be false
  • Slippery Slope: a series of increasingly unacceptable consequences is drawn
  • Complex Question: two unrelated points are conjoined as a single proposition
Appeals to Motives in Place of Support Changing the Subject
  • Attacking the Person:
    • (1) the person's character is attacked
    • (2) the person's circumstances are noted
    • (3) the person does not practise what is preached
  • Appeal to Authority:
    • (1) the authority is not an expert in the field
    • (2) experts in the field disagree
    • (3) the authority was joking, drunk, or in some other way not being serious
  • Anonymous Authority: the authority in question is not named
  • Style Over Substance: the manner in which an argument (or arguer) is presented is felt to affect the truth of the conclusion
Inductive Fallacies
  • Hasty Generalization: the sample is too small to support an inductive generalization about a population
  • Unrepresentative Sample: the sample is unrepresentative of the sample as a whole
  • False Analogy: the two objects or events being compared are relevantly dissimilar
  • Slothful Induction: the conclusion of a strong inductive argument is denied despite the evidence to the contrary
  • Fallacy of Exclusion: evidence which would change the outcome of an inductive argument is excluded from consideration
Fallacies Involving Statistical Syllogisms
  • Accident: a generalization is applied when circumstances suggest that there should be an exception
  • Converse Accident : an exception is applied in circumstances where a generalization should apply
Causal Fallacies
  • Post Hoc: because one thing follows another, it is held to cause the other
  • Joint effect: one thing is held to cause another when in fact they are both the joint effects of an underlying cause
  • Insignificant: one thing is held to cause another, and it does, but it is insignificant compared to other causes of the effect
  • Wrong Direction: the direction between cause and effect is reversed
  • Complex Cause: the cause identified is only a part of the entire cause of the effect
Missing the Point
  • Begging the Question: the truth of the conclusion is assumed by the premises
  • Irrelevant Conclusion: an argument in defense of one conclusion instead proves a different conclusion
  • Straw Man: the author attacks an argument different from (and weaker than) the opposition's best argument
Fallacies of Ambiguity
  • Equivocation: the same term is used with two different meanings
  • Amphiboly: the structure of a sentence allows two different interpretations
  • Accent: the emphasis on a word or phrase suggests a meaning contrary to what the sentence actually says
Category Errors
  • Composition: because the attributes of the parts of a whole have a certain property, it is argued that the whole has that property
  • Division: because the whole has a certain property, it is argued that the parts have that property
Non Sequitur Syllogistic Errors Fallacies of Explanation
  • Subverted Support (The phenomenon being explained doesn't exist)
  • Non-support (Evidence for the phenomenon being explained is biased)
  • Untestability (The theory which explains cannot be tested)
  • Limited Scope (The theory which explains can only explain one thing)
  • Limited Depth (The theory which explains does not appeal to underlying causes)
Fallacies of Definition
  • Too Broad (The definition includes items which should not be included)
  • Too Narrow (The definition does not include all the items which shouls be included)
  • Failure to Elucidate (The definition is more difficult to understand than the word or concept being defined)
  • Circular Definition (The definition includes the term being defined as a part of the definition)
  • Conflicting Conditions (The definition is self-contradictory)
References
For Educators... Please feel free to download the entire text (50 K) in plain-brown wrapper HTML (does not contain the last three sections - sorry). Permission is granted to use, abuse and reproduce this document in any way you wish provided (a) you don't claim copyright over it, (b) you don't charge anyone for using it, and (c) you indicate its original authorship. Read more on my views about copyright if you're curious.

13 August 1996