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Title: Introduction to Logic

Table of Contents:

Informal Fallacies:
Lecture Notes and Fallacy Examples

-Nonplussed Student- [woodcut by S.J. Swinbourne], _Picture_Logic_(London: Longmans, Green, 1875), 2.

“Nonplussed,” 1875, woodcut (adapted) by Alfred James Swinbourne [1]

From a psychological point of view, a fallacy is often defined as a mistake in reasoning or argumentation. Often fallacies are used for deceptive purposes and many of the informal fallacies described here are used for the manipulation of opinion.

Many of these mistakes in reasoning occur so often they deserve special study.

This section investigates informal fallacies — those dependent upon language. An informal fallacy is one that arises from the content of an argument (the meaning what is declared), not a fallacy arising from the grammatical structure (the syntax of how the argument is expressed).

Our classification of fallacies, like that of I.M. Copi's, is arranged in terms of mistakes in reasoning arising from appeals to irrelevant factors as well as mistakes arising from unsupported assumptions.

Nevertheless, as Joseph says in his An Introduction to Logic: “Truth may have its norm, but error is infinite in its aberrations, and they cannot be digested in any classification.” [2]

Not all irrelevant appeals or unsupported assumptions are fallacies. Fallacies only occur in argumentative discourse. Thus, if no argument is present in a passage, no fallacy can be present.


1. Alfred James Swinbourne, “Image: Nonplussed,” Picture Logic; or, The Grave Made Gay,” (London: Longmans, Green: 1875), 2.

2. H.W.B. Joseph, An Introduction to Logic (London: Clarendon Press, 1916), 569.

  • Nature of Fallacies

    Informal and formal fallacies are characterized in an introductory manner.



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