Formal fallacy

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In philosophy, a formal fallacy or a logical fallacy is a pattern of reasoning which 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 more generally to mean an argument which is problematic for any reason, whether it be a formal or an informal fallacy.

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 (e.g. appeal to authority), 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.

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. Many of the fallacies in the list below are best understood as being fallacies in this sense.

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

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

As modus ponens, the above argument contains no formal fallacies. 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. Of course, an argument could contain both an informal fallacy and a formal fallacy, 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.

And 3 certainly wasn't true prior to the 20th century.

Common examples

For a list of types of formal and informal fallacy, as well as examples of fallacious arguments, see Fallacy. For a concise list of "appeal to" fallacies, see Appeal (disambiguation).

See also

References

• 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.
• T. Edward Damer. Attacking Faulty Reasoning, 5th Edition, Wadsworth, 2005. ISBN 0-534-60516-8
• 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

• Logical Fallacies — a semi-ordered list with definitions
• The Fallacy Files by Gary N. Curtis — real examples posted regularly.
• ESGE Logical Fallacies — European Society for General Semantics
• Logical Fallacies .Info
• Bruce Thompson's Fallacy Page
• Stephen Downes Guide to the Logical Fallacies
• Logical Fallacies and the Art of Debate
• Logical Fallacies Quiz Ten common fallacies in an interactive test format.
• 42 informal logical fallacies explained by Dr. Michael C. Labossiere, including examples.
• On Informal Fallacies is a collection of one-off fallacies coined for specific, rhetorical purposes.
• Marilyn vos Savant explains Logical Fallacies