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Rhetorical Fallacies: Non Sequitur and Post Hoc, Ergo Propter Hoc

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Presentation on theme: "Rhetorical Fallacies: Non Sequitur and Post Hoc, Ergo Propter Hoc"— Presentation transcript:

1 Rhetorical Fallacies: Non Sequitur and Post Hoc, Ergo Propter Hoc
By: Jazmin Impastato

2 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.

3 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.

4 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.

5 Post Hoc, Ergo propter Hoc (False-cause 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.

6 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.

7 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.

8 Bibliography “Fallacies.” Handouts and Links Creative Commons Attributions. 5 April <http://www.unc.edu/depts/wcweb/handouts/fallacies.html>. “Logical fallacies.” Philosophical Society Philosophical society. 5 April <http://www.philosophicalsociety.com/Logical%20Fallacies.htm#post-hoc>. “Non Sequitur.” Bambooweb dictionary. Wikipedia. 5 April <http://www.bambooweb.com/articles/n/o/Non-sequitur.html>. “Non Sequitur.” International Society for Complexity, information, and design April <http://www.iscid.org/encyclopedia/Non_Sequitur>. Nordquist, Richard. “Non Sequitur.” Grammar and Composition. The New York Times Company. 5 April <http://grammar.about.com/od/mo/g/nonseqterm.htm>. “Post Hoc.” Fallacy Files April <http://www.fallacyfiles.org/index.html>. Whitman, Glen. “Logical Fallacies and the Art of Debate.” Argumentation. 29 January April <http://www.csun.edu/~dgw61315/fallacies.html#Non%20sequitur>.


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