Logical Fallacies

Unrepresentative Sample

Unrepresentative Sample

the sample relied upon in the premises is unrepresentative of the population in the conclusion

Overgeneralization

the conclusion is too broad for the premises used in support of it

Confuses a Sufficient and a Necessary Condition

Reversal without Negation or Negation without reversal of a principle (the argument fails to establish that a condition under which a phenomenon is said to occur is the only condition under which that phenomenon occurs)

Failure to Establish Sufficient Condition

A and B --> C. A exists, therefore C exists

Two Subabsolute Conditions Used to Draw Inference

Since some As are Bs and some Bs are Cs it follows that some As are Cs

Bad Analogy

Fails to take into account that two things that share a characteristic may have important differences between them

Rootless Analogy

when a comparative argument merely establishes a positive or negative comparison to a thing without also establishing that thing's objective relationship to the conclusion

Negative Analogy

Fails to take into account that just because two things are different doesn't mean they don't share important characteristics

Fails to Exclude Alternative Cause

assumes a causal relationship from a correlation when there is an explicit or implicit alternative cause

Mistakes Correlation for Causation

assumes a causal relationship from a positive or negative correlation (coincidence)

Common Cause

assumes a causal relationship from a positive or negative correlation when both the stated cause and stated effect might both be effects of a common cause

Causal Reversal

assumes a causal relationship from a correlation when it is just as likely that the stated effect caused the stated cause

Exclusive Causation

assumes that the establishment of a causal relationship means that there are no other causes for the effect and/or no other effects of the cause

Fails to Account for Degree of Effect

presumes that not all effects of a cause are equal in degree

Compound Effect

ignores the fact that effects are compound; what has happened in the past may not be possible today merely because it was possible before

Temporal Causal Flaw

presumes that just because one thing tends to occur after another that the first thing causes the second

Delayed Effect

assess the present of absence of causation without considering that the effect may be delayed / take longer to develop than the study allows

Inappropriate Authority

The authority relied upon does not have sufficient background in the subject in question

Biased Authority

relies upon an authority that has a vested interest in the outcome of the circumstance (they are self-reporting data that involves their performance; they are providing information about competitors or rivals)

Democracy Flaw

assumes that the opinion of the majority is sufficient authority in matters of fact

Missing the Point

arguing for a point that is not at issue or using irrelevant evidence

Absence of Evidence is not Evidence of Absence

failure to prove a claim as true does not constitute proof of the denial of the claim

Ad Hominem

attacking the proponent of a claim (personal behavior, associations, past actions) so as to avoid addressing the merits of their claim)

Circular

uses the conclusion to support the conclusion; assumes what it attempts to prove

Contradictory Evidence

uses two premises that cannot at the same time be true

Contradictory Conclusion

when the conclusion is at odds with a premise used to support it

Strawman

misdescribing an opponent's position in order to make it easier to disprove

Ambiguous Word Usage

allowing a key term or concept to change meaning over the course of the argument

Relative is Mistaken for Absolute

healthier does not mean healthy

A Change in Proportion is not a Change in Number

if a total is unknown, a proportional change of a component of that total may be caused by an increase in number of that component or a decrease in number of other components.

Frequency Flaw

presumes that two categories have equal frequencies in a population (usually related to likelihood of occurrence yielding higher or lower amounts in reality)

Substitutes One Group for a Different Group in the Statement of a Percentage

when comparing percentages of the same thing, do not change the group identity

False Equivalence

treats two different concepts as if they are identical

False Dichotomy

fails to account for a middle ground; assumes there are only two possible options

Correlation within Categories is Assumed to Exist Across Categories

The older you are the wiser you are. Greg is older than Mary. Therefore Greg is wiser than Mary

Crowded Primary Flaw

the best of a selection of three or more does not necessarily mean a majority approve of it

Part to Whole

assumes that just because each member of a set shares a characteristic, the set as a whole also shares that characteristic

Whole to Part

assumes that just because a set has a characteristic, each member of the set must also share that characteristic.

Flaw of Averages

presumes that an average describing a set also accurately describes each member of the set

English Department Economics

assumes money is not fungible in a bureaucracy

Can Be is not Must Be

uses premises that involve could, may, might, or the presence of incentives/motives and concludes that something will or must happen or that the incentive/motive will be acted upon.

Weakening is not Proving False

providing contrary evidence is not tantamount to demonstrating that the conclusion cannot be true, just that it is not proven true

Temporal Continuity

just because something has happened in the past does not mean it will happen in the future; the flaw of predicting the future without qualification

Perfect is the Enemy of the Good

assumes that any departure from the ideal is fatal to a project

A Partial Solution is not a Complete Solution

if any part of the problem remains, a proposed solution is therefore only partial

Mistakes Generalizations for Principles

generalizations are consistent with non-conforming cases, but principles are disproven by non-conforming cases

Arbitrary Preference

chooses one option over another without giving a reason

Fails to Run a Controlled Study

does not isolate the tested variable, making it impossible to know if another thing or combination of things affected the outcome

Incomplete Cost Benefit Argument

chooses one thing over another by giving an incomplete assessment of costs and benefits