Informal fallacy

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An informal fallacy (also presumption fallacy, soundness fallacy) is an argument that is formally valid but is unsound because of the lack of truth of one or more of its premises. Informal fallacies are characterised by the fact that although there is a connection between their premises and their conclusion — i.e. they have a valid form — their premises are unsupported. All informal fallacies are forms of question-begging. These tend to be more misunderstood and slightly more numerous than formal fallacies.

List of informal fallacies[edit]

The Math 101 (Spring 2007) handouts, Department of Mathematical Sciences, Northern Illinois University lists the following informal fallacies:[1][2]

  1. Appeal to Force: using force or the threat of force to gain acceptance to one's conclusion.
  2. Abusive (Ad hominem): instead of trying to disprove the truth of what is asserted, one attacks the person who made the assertion
  3. Circumstantial: An attempt to prove that an opponent ought to accept an argument because of the special beliefs and circumstances of your opponent.
  4. Argument from ignorance: Assertion that a statement is true because it has not been proven false.
  5. Appeal to pity: pity is appealed to for the sake of getting a conclusion accepted.
  6. Appeal to the People (Appeal to emotion): Attempt to win popular assent by arousing the feelings and enthusiasmWikipedia of the multitudes.
  7. False Authority: Use of the feeling of respect or admiration people have for a popular person to win assent to a conclusion, especially for matters outside the province of their special fields of authority.
  8. Accident: Attempt to discredit a general rule by taking a particular exception to that rule. What is true “in general” might not be universally true without qualification, because circumstances alter cases.
  9. Hasty generalization: Converse of the fallacy of accident, hasty generalization is when you make a conclusion based on atypical cases.
  10. False Cause (Post hoc, ergo propter hoc): Mistaking what is not the cause for a certain phenomenon for the real cause. Sometimes this fallacy occurs when one event precedes a second, and is therefore falsely claimed to be the cause of the second event.
  11. Begging the question: Assume as a premise for your argument the very conclusion you want to prove.
  12. Complex Question: presume a definite answer to a prior, unasked question.

Fallacies of ambiguity[edit]

  1. Irrelevant Conclusion: Argument purporting to establish a particular conclusion is directed to prove a different conclusion
  2. Equivocation: Use of expressions of double meaning in order to mislead.
  3. Grammatical Construction: Unclear statement because of the loose or awkward way its words are combined.
  4. Composition: Applying properties of parts of a whole to the whole itself.
  5. Division: Reverse of composition; what is true for the whole is true of its parts.

Other examples of informal fallacies are:

In example[edit]

P1: Half of all adult humans can grow beards.
P2: Sophia is an adult human female.
C: There is a 50% chance Sophia can grow a beard.

This is not a sound argument because the first premise is irrelevant — an irrelevance which means it is not a valid argument, either: the truth of its premises do not guarantee the truth of its conclusion. As such, it is a formal fallacy.

P1: The above argument is valid but unsound
P2: Arguments that are valid but unsound constitute an informal fallacy
C: The above argument constitutes an informal fallacy

This is not a sound argument because the first premise is not true — however, if it were true, the argument would be sound. As such, it is an informal fallacy.

Dixiecrat fallacy[edit]

See the main article on this topic: States' Rights Democratic Party

You know, it's really the Democrats who are racist. Want to know why? They're the party who started the KKK!

Usage of the Dixiecrat fallacy, and its lost irony[edit]

"Next time one of those stupid liberals tells you you’re a racist, you tell him it was the dirty, filthy, stinkin’ ni***r-lovin' democRats what started the KKK. You tell 'em that and it'll blow their minds because they'll realize it's the ni***rs that are the real racists."

Other informal fallacies[edit]

See also[edit]



  1. Informal Fallacies part 1 - Math 101, Spring 2007 handout, Department of Mathematical Sciences, Northern Illinois University
  2. Informal Fallacies part 2 - Math 101, Spring 2007 handout, Department of Mathematical Sciences, Northern Illinois University

External links[edit]