Post on 04-Jan-2016
transcript
LOGIC
A Very Short Introduction
Words
We need to define words!
Example:
Jack: “I love you.”Mary: “Wow!”
Mary thinks: Love means staying forever and getting married!
Jack thinks: Love means I’m really attracted to you at this particular moment.
Awkward.
DEFINE LOVE
Some say there are four different kinds…
1. Storge – liking2. Philia –friendship (shared interests)3. Eros – romantic desire4. Agape / Caritas – self-sacrificing
love (desires the good of the other)All are forms of wanting.
Step 1: InductionInduction starts with experience.
• Over the years, I meet a couple dozen people from Omaha and they are in every case extremely nice and kind.
• I call my friend and she doesn’t answer three times.• I didn’t think I would like books by Charles Dickens, but it turns
out that I really enjoyed David Copperfield and Great Expectations.
• I thought everybody from the South was polite, but then somebody with a Southern accent rammed me with her grocery cart.
Exercise 1:What is something you learned or concluded from repeated
experiences?
Repeated experiences lead to
INDUCTIVE LEAPS
Step 2: Forming Premises
• ALL people from Omaha are nice.• NO phone-calls to my friend get
answered.• SOME of Dickens’ books are
enjoyable.• SOME people are NOT polite.
Exercise 2: Express what you learned from repeated experiences as a simple statement.
A note about universals(all-statements):
If it’s not inherent to the thing, it could be otherwise:
For example: All squirrels are brown.There’s nothing about a squirrel that it
means it HAS to be brown.When it is inherent, that’s different.For example: All material things have a
gravitational pull.Gravitational pull is an intrinsic property of
matter.
DEDUCTION
Which now leads us to Step 3 in the reasoning process, namely…
Deductive Reasoning
Based on propositions derived from our experiences, we come to conclusions.
For example:All humans are mortal.
I am a human.Therefore, I am mortal.
The Pieces of Syllogisms
3 TERMSMinor term, Middle Term, Major Term
(Each appears twice.)
2 PREMISES (i.e., syllogistic propositions)Major premise contains the major term and the middle
term.Minor premise contains the minor term and the middle
term.
1 CONCLUSIONWhich joins the major and the minor terms.
Example Syllogism 1
Major Premise: All humans are risible.
Minor Premise: X is a human.Conclusion: Therefore, X is
risible.
Middle Term = “human”Major Term = “risible” (able to laugh)
Minor Term = “X”
Truth & Validity
• Is the conclusion of that syllogism VALID? Beings
that laugh
Humans
X
Is it TRUE?
Do we need a syllogism?
Logic can be somewhat like grammar:1. It reveals what we are already doing.2. As knowing about language can make
us better at using language, knowing about logic can make us better thinkers.
Thus: Onward!
Truth vs. Validity
Truththe correspondence of thought to
reality.
Validitywhether or not the syllogism holds.
Let’s look at some more examples.
Analyze these syllogisms:
Some men are dishonest.Joe is a man.
Therefore, Joe is dishonest
All girls are kind.Mary is a girl.
Therefore, Mary is kind
Enthymeme
An enthymeme is a rhetorical syllogism. It’s abbreviated, and premises are left out.
Example: “She’s coming from SCA, so she’ll be really nice.”
What is the implicit syllogism?
The implicit syllogism:
All SCA girls are nice.She is an SCA girl----------------------------------------------Thus, she is nice.
Questions?
End of PPT.