Friday, December 2, 2011

Logical Fallacy of the Week: Week 18, Informal Fallacies


Informal fallacies - We will now begin to explore the Informal fallacies – arguments that are fallacious for reasons other than structural (formal) flaws and which usually require examination of the argument's content. An informal fallacy is an argument whose stated premises fail to support their proposed conclusion. 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 from 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 generalization, can be roughly stated as:

p) A is an X
p) A is also a Y
c) therefore, all Xs are also Ys

If the populations X and Y are both too large to sample completely, then the statement is inductive. In such a case, a hasty generalization occurs when the number of Xs and Ys 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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