Informal fallacy

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An informal fallacy is an argument whose stated premises fail to support their proposed conclusion.[1] The deviation in an informal fallacy often stems from a flaw in the path of reasoning that links the premises to the conclusion. In contrast to a formal fallacy, the error has to do with issues of ratiocination manifest in language used to state the propositions; the range of elements that can be symbolized by language is broader than that which the symbolism of formal logic can represent. Informal fallacies of deductive reasoning contain a fundamental disconnect between the premises and the conclusion that renders the argument invalid. This disconnect often stems from the presence of a hidden co-premise that, if presented, would validate the argument.

Inductive informal fallacies are slightly different than their deductive counterparts, as 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 generalisation, 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.

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  1. ^ Kelley, D. (1994) The Art of Reasoning. W W Norton & Company, Inc. ISBN 0-393-96466-3

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