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 – liking 2.Philia –friendship (shared interests) 3.Eros – romantic desire 4.Agape / Caritas – self-sacrificing love (desires the good of the other) All are forms of wanting.

Step 1: Induction Induction 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 TERMS Minor 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 CONCLUSION Which 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 Truth the correspondence of thought to reality. Validity whether 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 girlsare nice. Sheis an SCA girl Thus, sheis nice.

Questions? End of PPT.