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Chapter 2: A Little Logic

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Desiderio IV Camitan

on 13 November 2016

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Transcript of Chapter 2: A Little Logic

LOGIC
Chapter 2:
A Little
the process of careful thinking
the science and the process of proper reasoning
a prerequisite of a good
argument
based on :
1. example
2. analogy
3. scientific research
4. vicious attack on
one's opponent
Arguments
Deduction
Induction
one argues for the truth of a conclusion by deducing a statement from a number of others
Some statements are assumed to be true from the outset.
All humans are mammals.
New statements are inferred
I am human. Therefore, I am a mammal.
Rule of Inference
A statement cannot be both true and false at the same time
a progression from one true statement to another
the second statement is established as true too because of the truthfulness of the first
Syllogisms
The major premise is a general claim, the minor premise is a particular claim.
All P's are Q's.
S is a P.
Therefore, S is a Q.
(major premise)
(minor premise)
(conclusion)
All birds have feather.
A chicken is a bird.
A chicken has feathers.
All cows are purple.
Socrates is a cow.
Therefore, Socrates is purple.
*Deduction assumes that if the premises are true then the conclusion will certainly be true.
*Arguments can be valid without being true!
if the argument follows:
All P's are Q's.
S is a P.
Therefore, S is a Q.
if it is coincides with reality.
in
All P's are Q's.
S is a Q.
Therefore, S is a P.
argument
All lemons are yellow.
Sam (the canary) is yellow
Therefore, Sam is a lemon.
All males have facial hair
Annie has facial hair
Therefore, Annie is a male.
*A sound argument needs to be both valid and true.
x
modus ponens
modus tollens
If P then Q.
P.
Therefore, Q.
If Socrates keeps annoying people, he will get in trouble.
Socrates won't stop annoying people.
Therefore, he will get into trouble.
If Dex drinks coffee after 6:00PM, he will have trouble sleeping
Dex drank coffee after 6:00PM
Therefore, Dex will have trouble sleeping.
If Paulene eats seafood, she will have allergies.
Paulene ate seafood
Therefore, Paulene will have allergies.
If P then Q.
Not Q.
Therefore, not P.
If you love me, you will wait for me.
You did not wait for me.
Therefore, you don't love me
If I am not Batman, then you should have a photo of Batman and I together.
You don't have a photo of us together.
Therefore, I am Batman.
fallacy of affirming the consequent
If Paulene eats seafood, she will have allergies.
Paulene has no allergies
Therefore, Paulene did not eat seafood.
If P then Q.
Q.
Therefore, P.
If you stay up too late, you'll miss breakfast.
You missed breakfast.
Therefore, you stayed up late.
If Paulene eats seafood, she will have allergies.
Paulene has allergies.
Therefore, Paulene ate seafood.
If today is Wednesday, then Mr. Camitan will be at iAcademy.
I saw Mr. Camitan at iAcademy.
Therefore, today must be Wednesday.
If P then Q.
Not P.
Therefore, not Q.
Kung bobotohan ninyo si Cayetano, may magsasabing "Mayor, mali iyan. Mayor, ito ang gawin natin."
Hindi ninyo binoto si Cayetano.
Wala tuloy magsasabing "Mayor, mali iyan. Mayor, ito ang gawin natin."
fallacy of denying the antecedent
If you report bad news about the war on drugs then you are biased.
You did not report bad news about the war no drugs.
Therefore you are not biased.
If you stay up too late, you will miss breakfast.
You did not stay up too late.
Therefore, you did not miss breakfast
this argument is an example of
reductio ad absurdum
or reduction to absurdity.
regardless of the apparent logic, the consequence is absurd.
does not guarantee the truth of their conclusions, even if all the premises are agreed to be true.
"It is common sense. Do you see animals mating with the same sex? Animals are better because they can distinguish male from female. If men mate with men and women mate with women they are worse than animals."
-Senator Emmanuel Pacquiao
Inductive arguments can be
strong
or
weak
depending on:
1. weight of the evidence for the conclusion
2. quality of the sample
3. the plausibility of the generalization
Generalization
from a number of particular cases is the most common form of inductive argument.
*no
inductive argument is ever deductively valid.
*it can be used to support virtually any statement of fact.
Jose Rizal is Jack the Ripper
Rizal is an ophthalmologist, the ripper is suspected to be a doctor.
Rizal can speak English, the ripper is believed to be an Englishman.
Rizal went to London in 1888, the killings started in 1888. Rizal left London in 1889, the killings stopped that same year.
Rizal is known to have many lovers, the ripper killed women.
Both Rizal and the Ripper's initials are "JR"
Duterte is Lincoln's incarnate
Before assuming presidency, both were provincial lawyers.
Both are the 16th president of their respective country.
Both are fond of federalism.
Both used the same hand gesture.
Sherlocke Holmes'
"amazing power of deduction."
is just inductive reasoning.
He draws factual conclusions from scattered and sometimes barely noticeable evidences.
Criticize
How to
Use Counterexamples
Any claim that takes the form "All X's are Y's" or "No A's are B's" can be refuted by pointing out a single counterexample.
Check for inconsistencies
A philosophy is considered inconsistent if the conclusions of its different argument contradict one another.
Rizal left London on January 1889, the last reaper-related killing was recorded on June 1889.
If an argument results in a
paradox
an argument is considered absurd.
God can do absolutely anything. He can create a mountain, he can move a mountain.
Can He create a mountain so large that He can't move it?
God can do anything that is logically possible.
This sentence is false.
There is a barber who shaves everyone in town who does not shave himself.
If you save everyone, who saves you?
Point out incoherence
Note if claims have virtually nothing to do with each other, or mean very little, or can be interpreted only in an absurd way.
examine logical fallacies
Activity: Examining Arguments
Examine the following arguments. Are they inductive or deductive arguments? Are they valid and sound? If they are invalid or unsound, why? Is there anything else wrong with them?
1. The philosopher from northern Greece is a well-known homosexual. Therefore, his claim that the universe is ultimately made up of atoms should be ignored.
2. Every event in the world is caused by other events. Human actions and decisions are events in the world. Therefore, every human action and decision is caused by other events.
3. If God exists, then life has meaning. God does not exist. Therefore, life has no meaning.
4. All cows are purple. Socrates is purple. Therefore, Socrates is a cow.
5. William James and John Dewey both called themselves pragmatists. They are the leading American philosophers. Therefore, all American philosophers are pragmatists.
6.We haven’t seen a fox all day. Therefore, there must be no foxes in the area.
7. If you don’t agree with me, I’m going to hit you.
8. God must exist; the Bible says so.
9. If she were innocent, she would loudly proclaim her innocence. She is loudly proclaiming her innocence. Therefore, she must be innocent.
10. “I have terrible news for you. Mary is going out with Frank. I called Mary on Saturday night, and she wasn’t home. Then I tried to call Frank, and he wasn’t home, either!”
Lex Luthor's Logic
1- God, by definition, is a Maximally Great Being
2- If God is perfectly good He would not want humanity to suffer or experience evil.
3- If God is all-powerful He could prevent humanity from suffering or experiencing evil.
4- Humanity suffers and experiences evil.
5- Therefore, God is either not perfectly good or not all-powerful (or both).
6- Therefore, God is not a Maximally Great Being.
7- Therefore, God, by definition, does not exist.
1- If God does not exist, then objective moral values and duties do not exist.
2- Evil exists (Lex and many atheists offers it as evidence against God).
3- Therefore, objective moral values and duties exist (some things are morally evil).
4- Therefore, God exists.
In response to the second premise
In response to the third premise
I agree that God is all-powerful; however, I must add that I do not believe God can do ALL things! Now before I am accused of being self-contradictory at best or a heretic at worst, consider this: can God make a triangle with four corners? Can God create a “married bachelor?” Can God sin? The answer to all of the above is a resounding, “NO!”
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