Logical Fallacies
Robyn Adams, Study Advice Service, February 2011
What is an argument?
• When we hear the word argument, we often think
of a disagreement
• In an academic sense, the word argument has a
different meaning
What is an argument?
– a final conclusion, based on at least one other fact
(premise)or conclusion
What is an argument?
Example:
– Premise 1:
“One must study effectively to have academic
success.”
– Premise 2:
“Paul studied effectively.”
– Conclusion:
“Therefore, Paul had academic success”
Do you see problems with this example?
What if Paul studied effectively, but
his exam technique was poor?
What if Paul was late for an exam?
Are there any other factors that
may have been overlooked?
What is a good argument?
In a sound argument:
– the premises should be true, and
– the conclusion should be assured, or very likely, based on the
premises.
Poorly constructed arguments are called
logical fallacies
Understanding their nature helps us to:
y Evaluate information critically
y Write better arguments
Logical fallacies
• Errors in reasoning (arguments in which we can find flaws)
• Often referred to in Latin (we’ll use English)
• They are used:
– Unintentionally: by those who don’t know how to fit pieces of
evidence together to build a good quality argument
– Intentionally: by those who know that they have weak arguments
• ~ 80 different types; different classification systems
The following slides present some
examples of logical fallacies
1. Personal attacks
• Attack on the personality, qualifications or background of another
to justify an argument
“You claim that this man is innocent, but you cannot be trusted since
you are a criminal as well.”
“Tobacco company representatives should not be believed when they
say smoking doesn't seriously affect your health, because they're just
defending their own multi-million-dollar financial interests.”
(Wikipedia 2008) Can you
trust this source? Possibly!
Still, NEVER use Wikipedia
in your academic studies –
academics do not accept it
as a reliable source
2. Appeal to popularity
“Bandwagon” fallacy
y If everyone else does/believes/uses it, so should I
“Lloyds TSB: Britain’s most popular home insurance
provider” (Lloyds TSB Insurance Services 2009)
Does their popularity mean that their insurance products
are of good quality or value?
3. Appeal to Traditions
“We make our furniture in the best way; the old way.
(And it’s every bit as uncomfortable as it always was.)” (Pirie 1985)
John Lewis Gable Large Sofa with “old-school
elegance” (John Lewis 2009)
£1275
4. Anecdotal Evidence
“I suffered with migraines at least 3
times a week, irritable bowel
syndrome and an overall feeling of
fatigue. I had my first appointment
with you in March of 2004 and my
life has changed forever. Within one
month my headaches were nonexistent. I didn't have any of the IBS
problems and I am far less fatigued,
even at the end of a 12 hour work
day. I thank you for helping me have
a healthier and happier life.”
(Homeopathic Wellness Centre 2006)
4. Anecdotal Evidence
• Biased – based on an
unsubstantiated opinion
• Small sample size (Can the
treatment be deemed effective based
on one person’s description?)
• Guilty of other fallacies
– After it therefore because of it – see next
slide
• Often used in advertising: can you
find any other examples?
5. After it, therefore because of it
In the previous example:
The person’s condition improved after the homeopathic
treatment. Does this mean that it was the homeopathic
treatment that helped?
...or could there have been another reason?
5. After it, therefore because of it
• Another example: Peas and illegitimate birth
• “Immediately after the introduction of canned peas
to Britain, the illegitimate birthrate shot up to a
new high, from which it did not decline until frozen
peas edged canned peas out of the market. The link
is all too obvious.” (Pirie 1985)
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Logical Fallacies Resources
Here are some useful online logical fallacies resources:
Curtis, G.N. (2003) The Fallacy Files [online] Available: http://www.fallacyfiles.org/index.html (Accessed 14
February 2011)
Gracyk, T. (2003) Explanations of Basic Fallacies [online] Available:
http://www.mnstate.edu/gracyk/courses/phil%20110/fallaciesexplained.htm (Accessed 14 February
2011)
Holt, T. (2006) Logical Fallacies [online] Available: http://www.logicalfallacies.info/ (Accessed 14 February
2011)
Labossiere, M.C. (1995) ‘Fallacies’ [online] The Nizkor Project, Available:
http://www.nizkor.org/features/fallacies/ (Accessed 14 February 2011)
Purdue Online Writing Lab (2009) Logical Fallacies [online] Available:
http://owl.english.purdue.edu/owl/resource/659/03/ (Accessed 14 February 2011)
Yoder, B. (no date) The Fallacy Zoo [online] Available: http://www.goodart.org/fallazoo.htm (Accessed 14
February 2011)
References
Gracyk, T. (2003). Explanations of Basic Fallacies [online] Available:
http://www.mnstate.edu/gracyk/courses/phil%20110/fallaciesexplained.htm (Accessed 23 June
2008)
John Lewis (2011) John Lewis Sofas [online] Available:
http://www.johnlewis.com/Home+and+Garden/Sofas/Sofas/SubCategory.aspx (Accessed 2 April
2011)
Lloyds TSB Insurance Services (2009) Lloyds TSB Insurance [online] Available:
http://www.insurance.lloydstsb.com/personal.asp (Accessed 27 February 2009)
Homeopathic Wellness Centre (2006) Health & Balance Testimonials [online] Available:
http://www.homeopathicwellness.com/testimonials.htm (Accessed 24 February 2009).
Pirie, M. (1985) The book of the fallacy: A training manual for intellectual subversives, Routledge &
Kegan Paul, London
Wikipedia (2008) Fallacy [online] Available: http://en.wikipedia.org/wiki/Logical_fallacy (Accessed 20
June 2008)