Formal fallacy

In philosophy, a formal fallacy is a pattern of reasoning that is always wrong. This is due to a flaw in the logical structure of the argument which renders the argument invalid. A formal fallacy is contrasted with an informal fallacy, which may have a valid logical form, but be false due to the characteristics of its premises, or its justification structure.

The term fallacy is often used generally to mean an argument that is problematic for any reason, whether it is formal or informal.

The presence of a formal fallacy in a deductive argument does not imply anything about the argument's premises or its conclusion. Both may actually be true, or even more probable as a result of the argument, but the deductive argument is still invalid because the conclusion does not follow from the premises in the manner described. By extension, an argument can contain a formal fallacy even if the argument is not a deductive one; for instance an inductive argument that incorrectly applies principles of probability or causality can be said to commit a formal fallacy.

"Fallacious arguments usually have the deceptive appearance of being good arguments." Recognizing fallacies in everyday arguments may be difficult since arguments are often embedded in rhetorical patterns that obscure the logical connections between statements. Informal fallacies may also exploit the emotional, intellectual, or psychological weaknesses of the audience. Having the capability to recognize fallacies in arguments is one way to reduce the likelihood of such occurrences.

A different approach to understanding and classifying fallacies is provided by argumentation theory. In this approach, an argument is regarded as an interactive protocol between individuals which attempts to resolve their disagreements. The protocol is regulated by certain rules of interaction and violations of these rules are fallacies.

Such fallacies are used in many forms of modern communications where the intention is to influence behavior and change beliefs. Examples in the mass media today include but are not limited to propaganda, advertisements, politics, newspaper editorials and opinion-based “news” shows.

In contrast to informal fallacy

As modus ponens, the following argument contains no formal fallacies.

1. If P then Q
2. P
3. Therefore Q

If statements 1 and 2 are true, it will absolutely follow that statement 3 is true. However, it may still be the case that statement 1 or 2 is not true. For example:

1. If a scientist makes a statement about science, it is correct.
2. Albert Einstein states that all quantum mechanics is deterministic.
3. Therefore it's true that quantum mechanics is deterministic.

In this case, statement 1 is false. The particular informal fallacy being committed in this assertion is argument from authority. By contrast, an argument with a formal fallacy could still contain all true premises:

1. If Bill Gates owns Fort Knox, then he is rich.
2. Bill Gates is rich.
3. Therefore, Bill Gates owns Fort Knox.

Though, 1 and 2 are true statements, 3 does not follow because the argument commits the formal fallacy of affirming the consequent.

An argument could contain both an informal fallacy and a formal fallacy yet have a correct conclusion, for example, again affirming the consequent:

1. If a scientist makes a statement about science, it is correct.
2. It's true that quantum mechanics is deterministic.
3. Therefore a scientist has made a statement about it.

Common examples

Main article: List of fallacies

See also

• Apophasis
• Cogency
• Cognitive bias
• Demagogy
• Fallacy
• Fallacies of definition
• False statement
• Informal logic
• Invalid proof
• Paradox
• Sophism
• Soundness
• Validity

References

Notes

Bibliography

• Aristotle, On Sophistical Refutations, De Sophistici Elenchi.
• William of Ockham, Summa of Logic (ca. 1323) Part III.4.
• John Buridan, Summulae de dialectica Book VII.
• Francis Bacon, the doctrine of the idols in Novum Organum Scientiarum, Aphorisms concerning The Interpretation of Nature and the Kingdom of Man, XXIIIff.
• The Art of Controversy | Die Kunst, Recht zu behalten — The Art Of Controversy (bilingual), by Arthur Schopenhauer
• John Stuart Mill, A System of Logic — Raciocinative and Inductive. Book 5, Chapter 7, Fallacies of Confusion.
• C. L. Hamblin, Fallacies. Methuen London, 1970.
• Fearnside, W. Ward and William B. Holther, Fallacy: The Counterfeit of Argument, 1959.
• Vincent F. Hendricks, Thought 2 Talk: A Crash Course in Reflection and Expression, New York: Automatic Press / VIP, 2005, ISBN 87-991013-7-8
• D. H. Fischer, Historians' Fallacies: Toward a Logic of Historical Thought, Harper Torchbooks, 1970.
• Douglas N. Walton, Informal logic: A handbook for critical argumentation. Cambridge University Press, 1989.
• F. H. van Eemeren and R. Grootendorst, Argumentation, Communication and Fallacies: A Pragma-Dialectical Perspective, Lawrence Erlbaum and Associates, 1992.
• Warburton Nigel, Thinking from A to Z, Routledge 1998.
• Sagan, Carl, The Demon-Haunted World: Science As a Candle in the Dark. Ballantine Books, March 1997 ISBN 0-345-40946-9, 480 pgs. 1996 hardback edition: Random House, ISBN 0-394-53512-X, xv+457 pages plus addenda insert (some printings).

External links

• The Fallacy Files by Gary N. Curtis – real examples posted regularly
• ESGE Logical Fallacies – European Society for General Semantics
• Logical Fallacies .Info
• Stephen Downes Guide to the Logical Fallacies
• Marilyn vos Savant explains Logical Fallacies