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Three Basic Fallacies. All the fallacies we deal with are forms of three basic fallacies:. - Irrelevant Reason . - Hasty Conclusion. - Problematic Premise . Irrelevant Reason (relevant?). Also called “Non-Sequitur” (“It does not follow”). The arguer puts forth a

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three basic fallacies
Three Basic Fallacies
  • All the fallacies we
  • deal with are forms of
  • three basic fallacies:

- Irrelevant Reason

- Hasty Conclusion

- Problematic Premise

irrelevant reason relevant
Irrelevant Reason (relevant?)
  • Also called “Non-Sequitur”
  • (“It does not follow”)
  • The arguer puts forth a
  • premise which, though it
  • may be true, has nothing to
  • do with the conclusion.
irrelevant reason
Irrelevant Reason

E.g.: A former Health

Minister, when asked in the

Commons about the food value

of Corn Flakes, responded:

“The milk you have with your

Corn Flakes has great

nutritional value.”

hasty conclusion sufficient
Hasty Conclusion (sufficient?)
  • Even when the premises are
  • relevant, they may not give
  • enough evidence to support
  • the conclusion.
  • Beware of anecdotal
  • evidence -- relying on only
  • one or two “incidents.”
hasty conclusion
Hasty Conclusion

E.g.: “University profs really

have it pretty easy. We have

a cottage next door to a prof, &

he’s there from late April right

through September, fishing and


problematic premise acceptable
Problematic Premise (acceptable?)
  • Each premise of an argument
  • should be defended, unless it
  • is already clearly true because
  • it is common knowledge, or
  • offered by an expert witness,
  • or is only being offered for
  • the sake of argument, etc.
problematic premise
Problematic Premise

E.g.: “Many young people who

today hold responsible jobs were

once the recipient of the lash, &

if there are any bleeding hearts

who think this is callous and

inhuman, let them read

Proverbs …”

to sum up
To Sum Up:
  • Irrelevant reason is a strong
  • charge: an argument guilty of
  • it must be abandoned, and
  • the arguer must start over.
to sum up1
To Sum Up:
  • Hasty Conclusion is a weaker
  • charge; it just means more
  • evidence needs to be given
  • before the conclusion can be
  • accepted -- not that the basic
  • argument and conclusion are
  • necessarily wrong.
to sum up2
To Sum Up:
  • Problematic Premise is the
  • weakest charge of all: it just
  • means the arguer needs to
  • supply more evidence for one of
  • his or her premises.

To SumUp:

  • an argument is not a fight;
  • it is an attempt to show
  • evidence in support of a
  • position or belief
  • an informal fallacy is an
  • argument with problems
  • in its premises
to sum up3
To Sum Up:


It is not enough to label an

argument a fallacy -- you

must be able to explain

why the argument is



Adapted from Johnson, R.H. and Blair, J.A. Logical Self-Defense (First Edition). Toronto, McGraw-Hill Ryerson, 1977