Logical Fallacies
A question to get us started…
• Tell me about what is logically wrong with this statement.
Why isn’t it convincing? What other problems does it have?
• “Every year in California, many students fail to pass the exit
exam. I believe that laziness is the reason for so many
failures. I have known several students who were unable to
pass, even after two or three tries, and all of them spent
more time doing other things than studying. I don’t think
schools should waste money helping lazy students like the
ones I know pass the test when they take it a second time.
Besides, if they’d paid attention in the first place in school
they wouldn’t have a problem passing the test. I paid
attention, and the test was easy for me.”
What is a fallacy?
• The previous slide contained an example of a
logical fallacy.
• Definition of fallacy: a misleading or unsound
argument. Any of various types of erroneous
reasoning that render arguments logically
unsound. (“erroneous” means “containing an
error”)
• See the handout for some common logical
fallacies
Why are logical fallacies tricky?
• Logical fallacies are tricky because they sound
good on the surface. At first glance, why
might the statement from our class example
be a little bit convincing? Look at the example
fallacies provided on the handout. Which ones
look good on the surface?
Logical Fallacies in the Media
• Where do we see logical fallacies? In the
media? In advertisements?
• Logical fallacies are not always as easy to spot
as the ones that I have provided for you. Be a
savvy reader. Be aware of author biases and
of these patterns we have discussed. If you
see these fallacies in something you read,
question them.
How can you fix a logical fallacy?
• If you catch yourself or a peer in a logical fallacy, how
do you fix it?
• Moderate your language. One of the fundamental
rules of persuasive writing is “Don’t make claims you
can’t prove.” Also, if you make a sweeping
generalization and the audience can think of even ONE
example that disproves your generalization, you’ve lost
credibility with your reader.
• Give more specifics – this especially helps with proof
by too few examples, allness, and oversimplification
Fixing logical fallacies
• Allow for complexity – this definitely helps with
oversimplification and either/or reasoning
• Avoid common, over the top phrasing – say
things in a new way
• Build credibility – your own, and that of your
sources. Show yourself to be knowledgeable and
reasonable, and your sources to be trustworthy.
• Look at the big picture – think of various
people/issues who might be affected by your idea
and consider them before making blanket
statements.