Rhetorical Fallacies: Non
Sequitur and Post Hoc, Ergo
Propter Hoc
By: Jazmin Impastato
Non Sequitur
Definition:
It is Latin for “It does not follow.”
A fallacy where the conclusion does not make sense with what
was previously said. When the evidence does not support the
claim.
There are two types of non sequitur:
-Affirming the consequent: When the argument doesn’t make
sense. The conclusion is not necessarily the cause of the
premises.
-Denying the antecedent: The second sentence denies the
first sentence.
Non sequitur can also be random comments that aren’t relevant to
the discussion.
Examples
Example of affirming the consequent:
1. If A then B. (If I am a monkey, I am a mammal.)
2. B. (I am a mammal.)
3. Therefore, A. (Therefore, I am a monkey.)
The argument does not make sense. There are different kinds of
mammals, not just monkey’s.
Example of denying the antecedent:
1. If A then B. (If I am in Tokyo, I am in Japan.)
2. Not A. (I am not in Tokyo.)
3. Therefore, not B. (Therefore, I am not in Japan.)
The speaker could be in other places in Japan.
If either of the these examples had “If and only if A, then B" as their
first premise, then they would be valid and non-fallacious.
More Examples
Many other types of known non sequitur argument forms have been classified
into many different types of logical fallacies. In everyday speech and
reasoning, an example might be: "If my hair looks nice, all people will love
me." There is no real connection. Advertising typically applies this kind of
'deduction'. Another example: "If I read a book it will rain."
Here is another example (By Jack Handey):
One in every five people is Chinese.
There are five people in my family.
There's me, my mom and my dad, my brother Colin, and my brother Ho-
Cha-Chu.
I think it's Colin.
Post Hoc, Ergo propter Hoc (Falsecause fallacy)
Definition:
Means “after this, therefore because of this.”
The Post Hoc Fallacy is when you assume that the first thing
caused the second thing, but that is not always the case. If you
think the first thing caused the second thing, then you have to test
it somehow, you can’t just assume. For example, if you see
lightning and then it snows, you can’t assume the lightening
caused it to snow, you have to test it out somehow and prove your
claim.
Example: When a sick person is treated by a witch doctor, or a
faith healer, and becomes better afterward, superstitious people
conclude that the spell or prayer was effective. Since most
illnesses will go away on their own eventually, any treatment will
seem effective by Post Hoc thinking.
Examples
If Jack sneezes and Jill jumps, it does not necessarily mean
that the sneezing caused Jill to jump. Jill’s seeing of a mouse
might have caused her jumping.
A young man walks by a neighbor's house and sees a cat
scurrying away; he looks up and sees a giant hole in the
window. The hole, he infers, must have been caused by the
cat, who fell through the pane. The inference is hasty, because
the hole might have been caused by a number of things.
More Examples
President Jones raised taxes, and then the rate of
violent crime went up. Jones is responsible for the rise
in crime. This might not be true. The increase in taxes
might or might not be one factor in the rising crime
rates, but the argument hasn't shown us that one
caused the other.
To avoid this post hoc fallacy, you need to give some
explanation of the process by which the tax increase is
supposed to have produced higher crime rates.
Bibliography
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<http://www.unc.edu/depts/wcweb/handouts/fallacies.html>.
“Logical fallacies.” Philosophical Society. 2001. Philosophical society. 5 April 2009.
<http://www.philosophicalsociety.com/Logical%20Fallacies.htm#post-hoc>.
“Non Sequitur.” Bambooweb dictionary. Wikipedia. 5 April 2009. <http://www.bambooweb.com/articles/n/o/Non-sequitur.html>.
“Non Sequitur.” International Society for Complexity, information, and design. 2001. 5 April 2009.
<http://www.iscid.org/encyclopedia/Non_Sequitur>.
Nordquist, Richard. “Non Sequitur.” Grammar and Composition. The New York Times Company. 5 April 2009.
<http://grammar.about.com/od/mo/g/nonseqterm.htm>.
“Post Hoc.” Fallacy Files. 2001. 5 April 2009. <http://www.fallacyfiles.org/index.html>.
Whitman, Glen. “Logical Fallacies and the Art of Debate.” Argumentation. 29 January 2001. 5 April 2009.
<http://www.csun.edu/~dgw61315/fallacies.html#Non%20sequitur>.