Informal Reasoning
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Agenda
Introduce Informal Reasoning
Reflect on Informal Reasoning
END GOAL: Is informal reasoning reliable?
Question 1
What is the difference between a prejudice, a generalization, and a scientific law?
Informal Reasoning
Post hoc ergo hoc
Ad hominem
Circular Reasoning
Special Pleading
Equivocation
Ad Ignorantiam
False Analogy
False Dilemma
Hasty Generalization
Loaded Questions
Post hoc ergo propter hoc
Literally, “after this, therefore on account of this”
Because one thing (b) follows another thing (a), then A must be the cause of B.
EXAMPLE:
Murder rate goes up after abolition of the death penalty. Therefore, getting rid of the death penalty increased the murder rate.
FLAW: it COULD be the case, but it might not be
Post hoc ergo propter hoc
Even when one event USUALLY follows another, it is still does not NECESSARILY mean the two are connected.
CAREFUL: claiming something is a fallacy when not
Tobacco Company
Casual Connection vs. Fallacy (red wine and heart)
Ad hominem
Literally: “Against the man”
Attack/Support the person rather than the argument (VESTED INTEREST)
Rather than critique an idea or argument, a person is being attacked
USUALLY used to attack someone, but can also be done to support….Einstein liked it, so it has to be good!
Question 2
Are we ever justified in rejecting what someone says solely on the basis of who they are?
Circular Reasoning
You assume the truth of something that you are supposed to be proving
What at first looks like an argument is really just a reassertion of their position
EXAMPLE: I know that Jesus is the Son of God because he said he was, and the Son of God would not lie.
Special Pleading
Double standard – making an exception in your own case that you would not find acceptable for someone else
Example: I know there is a drought and we need save water….but MY flowers are prize winning daffodils!
Equivocation Syllogisms with different senses/meanings
A hamburger is better than nothing
Nothing is better than good health.
Therefore a hamburger is better than nothing.
Two different definitions of nothing (not having anything vs. there is not anything)
Ad Ignorantiam
Something is true on the grounds that there is no evidence to disprove it
Loch Ness Monster
Bog Foot?
False Analogy
Assume that because two things are similar in one respect they must also be true in other ways
“Just as in time the gentle rain can wear down the tallest mountains, so, in human life, all problems can be solved by patience and quiet persistence.”
False Dilemma
The fallacy of deciding there are only two options, when in reality there are a wide range of possibilities
Do those who advocate an increase in military funding what to see schools and hospitals close?
Loaded Questions
A question that contains a built in assumption that has not been justified and may be false.
Do you always cheat on exams?
Can be a statement: That teacher was not drunk today.
Quote 1
“What’s so fascinating about New Yorkers is that each person has a whole lexicon of personal logic in the way that they decipher and do what has to be done to enjoy, stay alive, take pleasure in this place.” –Spalding Gray
What does this quote mean?
Is it true only of New Yorkers?
Quote 2
“When dealing with people, remember you are not dealing with creatures of logic, but creatures of emotion.” – Dale Carnegie
What does this quote mean?
Agree/Disagree?
How does this quote and your position on it affect your answer to yesterday question about perception vs. reasoning?
Quote 3
“All of our reasoning ends in surrender to feeling.” –Blaise Pascal
What does this quote mean?
Do you agree or disagree?
What are some examples you see in our society/in your own life?
