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An informal fallacy is an argument whose stated premises fail to support their proposed conclusion. Informal fallacies often come about because of an error in reasoning. The premises are then erroneously linked to the conclusion. In contrast to a formal fallacy, the error has to do with issues of inference because language is used to state the propositions; natural language allows to say more than the symbolism of formal logic can represent. All informal fallacies of deductive reasoning contain a fundamental disconnect between the premises and the conclusion. This makes the argument invalid. The disconnect often arises because there is a hidden co-premise. If this co premise were stated, it would validate the argument.
Inductive informal fallacies are slightly different from their deductive counterparts, because their merit rests in the inductive strength of the premise-conclusion link rather than in the presence of hidden premises. For instance, the fallacy of hasty generalization, can be roughly stated as:
- p) S is a P
- p) S is also a Q
- c) therefore, all Ps are also Qs
If the populations of P and Q are both too large to sample completely, then the statement is inductive. In such a case, a hasty generalization occurs when the number of Ps and Qs is insufficient to represent the respective populations. It is important to distinguish between a principle of reasoning (deductive or inductive) and the premise of an argument.
References[change | edit source]
- Kelley, D. (1994) The Art of Reasoning. W W Norton & Company, Inc. ISBN 0-393-96466-3
- In other words, when you fail to mind your Ps and Qs!
- Damer, T. E.; Rudinow, J.; Barry, V. E.; Munson, R.; Black, A.; Salmon, M. H.; Cederblom, J.; Paulsen, D.; Epstein, R. L.; Kernberger, C.; Others, (2009). Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (6E ed.). Wadsworth. ISBN 9780495095064. http://www.duxbury.com/cengage/instructor.do?product_isbn=9780495095064&disciplinenumber=5.