Homepage > Logic > Syllabus > Informal Fallacies

Summary of the Informal Fallacies

 Key to the Argument Structures L = Locutor, the person talking p, s = statements x, y = events, circumstances

1. Ad ignorantiam (argument from ignorance)

 p is unproved —————         Not p is true OR Not p is unproved. ——————— p is true.

E.g., There is absolutely no evidence to suggest that you won’t do well in logic; therefore, we may conclude that you will do well.

or

E.g., There of no evidence to suggest that you will do well in logic; therefore we may safely conclude that you will not do well.

2. Ad verecundiam (argument from authority)

Authority on x, L, says accept p.
p is outside the scope of subject x.
————————————––
p is true.

E.g., H. L. A. Jenkins, the noted international rose expert, has publicly stated that logic is essential to a life of excellence; consequently, it must be so.

3. Complex Question

How (or why) is p true?
————————————–
p is true.

E.g., When are you going to stop fooling around and begin to take you college education seriously? You will only benefit yourself if you start studying effectively.

4. Ad hominem (argument against the person)

L says p.
L is a bad (good) person.
—————————–
p is false (true).

E.g., You can’t believe what Professor Smith says about teacher’s salaries, because as a teacher himself, naturally he would be in favor of more money.

5. Accident

Rule or general statement p is true in circumstances x.
————————————–———————–
p is true in circumstance y.

E.g., Logic fulfills the Social Science Elective at Tennessee State, so a Logic course must be a social science.

6. Converse Accident (hasty generalization)

p is true in circumstance x.
——————————
p is true in more general circumstance y.

E.g., Not one person spoke to me on the way to the Library; Lander University is not as friendly as I was led to believe.

7. False Cause

x is related to (or is followed by) y
————————————–—
x caused y.

E.g., Since Jack sat in the back of the class and made an A on the last test, maybe I should sit there too.

or

E.g., Napoleon became a great emperor since he was so short.

8. Petitio principii (circular argument)

 p is true. q is true. r is true. ———– p is true OR p is true. ———– It is not the case that not p is true.

E.g., Logic is an essential course because it is required at many colleges. It is required because the ability to reason is vital, and it is vital because logic is essential.

9. Ad populum (argument from popular appeal)

 Snob Appeal:   L says p. L is in the elite. --------------------- p is true. OR Bandwagon: The majority believe p. ----------------------- p is true.

E.g., Snob Appeal: You have chosen the good life and a life of distinction, so now you need Four Roses Furniture to show that you have arrived.

E.g., Bandwagon: This logic course must be a good course because most people believe it is.

10. Ad misericordiam (argument from pity or misery)

L says p.
L deserves pity because of x.
———————————
p is true.

E.g., Mary will be broken hearted if she does not get an A in logic; therefore, she ought to get one.

11. Ignoratio elenchi (irrelevant conclusion)

More often, ignoratio elenchi is called a non sequitur. Since fallacies of relevance are informal, there is no complete standard classification of the ways people can make mistakes in arguments. This category of informal fallacy is a "catch all" type. If a fallacy of relevance does not clearly fit into one of the common fallacies described above, it should be identified as this fallacy.

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