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Stephen Downes

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Many kudos are owed to Stephen Downes, the logician who originally authored this list of fallacies and made it freely available on the Web. His basic structure remains. A mirror of Downes' original site can be found here.

Accent

Emphasis is used to suggest a meaning different from the actual content of the proposition. ... » Go

Division

Because the whole has a certain property, it is argued that the parts have that property. ... » Go

Conjunction (and)

The proposition P and Q is true if and only if both P and Q are true. It is false otherwise. ... » Go

Conditional (if-then)

The proposition If P then Q is true if and only if either P is false or Q is true. It is false only when ... » Go

Disjunction (or)

The proposition P and Q is true if and only if either P or Q are true. It is false only if both P and ... » Go

Too Broad

The definition includes items which should not be included. ... » Go

Composition

Because the parts of a whole have a certain property, it is argued that the whole has that property. ... » Go

Insignificance

One thing is held to cause another, and it does, but it is insignificant compared to other causes of the effect. ... » Go

Joint Effect

One thing is held to cause another when in fact both are the effect of a single underlying cause. ... » Go

Failure to Elucidate

The definition is harder to understand than the term being defined. ... » Go

Non-Support

The explained phenomenon does not in fact occur, or there is no evidence that it does occur. ... » Go

Amphiboly

An amphiboly occurs when the construction of a sentence allows it to have two different meanings. ... » Go

Irrelevant Conclusion

An argument which purports to prove one thing instead proves a different conclusion. ... » Go

Straw Man (Invidious Comparison)

The author attacks an argument which is different from, and usually weaker than, the opposition's best argument. ... » Go

Four Terms

The fallacy is committed when a standard form categorical syllogism contains four terms. ... » Go

Undistributed Middle

The middle term in the premises of a standard form categorical syllogism never refers to all of the members of the category it describes. ... » Go

Illicit Major

The predicate term of the conclusion refers to all members of that category, but the same term in the premises refers only to some members ... » Go

Circular Definition

The definition includes the term being defined as a part of the definition. ... » Go

Propositions

A logical operator joins two propositions to form a new, complex, proposition. ... » Go

Truths

A proposition is true if and only if what it says about the world is in fact the way it is. ... » Go

Negation (not)

The proposition Not P is true if and only if P is false. It is false only if P is true. ... » Go

Biconditional (if-and-only-if)

The proposition P if and only if Q is true if and only if both P and Q are true, or if both P and ... » Go