From a psychological point of view, a fallacy is often
defined as a mistake in reasoning used for deceptive purposes; however, many
fallacies are, in fact, not deceptive to most persons. Even so, many
of the informal fallacies are often used in 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 said, not the grammar in terms of how
the argument is expressed).
Our account of fallacies is in the tradition of I. M. Copi's
presentation: he reveals that some mistakes in reasoning arise from appeals to irrelevant factors
and others from unsupported assumptions.
Nevertheless, as Joseph says in his Introduction to Logic (569):
"Truth may have its norm, but error is infinite in its aberrations, and
they cannot be digested in any classification."
Not all irrelevant appeals and unsupported assumptions are fallacies. Fallacies
occur in argumentative discourse. Thus, if no argument is offered, no fallacy
Links to Lecture Notes:
Informal and formal fallacies and characterized in an introductory
FALLACIES OF RELEVANCE
The argument from ignorance is
The argument from irrelevant appeal
to authority is characterized.
The argument concerning the attack of a
person's character or circumstances is characterized.
The argument based upon what most or
all people think or believe is characterized.
The argument concerning the appeal to
pity or a related emotion to gain the acceptance of a conclusion is
- Ad Baculum
The argument based upon the appeal to force
or threats in order to bring about the acceptance of a conclusion is
The fallacy involving an irrelevant
conclusion is discussed here as a "catch-all" category for
fallacies not clearly identifiable as any of the other fallacies
FALLACIES OF PRESUMPTION
The fallacy of complex question is
discussed, and several typical examples are presented.
- False Cause
The fallacy of false cause and its forms as non
causa pro causa and post hoc ergo propter hoc is disussed
Petitio principii (viciously
circular reasoning) is described and several examples are noted.
The fallacy of Accident is based upon the
limited applicability of a "glittering generality"—from a
generalization as a premiss, an atypical particular conclusion is
claimed to follow.
Converse Accident or hasty
generalization is the fallacy of drawing a general conclusion based on
one or several atypical instances.
Twenty-five self-test questions are
presented with links to other exercises.
A summary of some
common informal fallacies is outlined, and examples are provided.