Logic Practice
An argument can be both invalid and sound. True or False
False
Disjunctive syllogism
Valid use of "or"
Invalid "if... then"
1. Affirming the consequent 2. Denying the antecedent 3. Hypothetical fallacy
Soundness
1. An argument that is always valid 2. Must have the premises and be true
Valid argument
1. Conforms to rules of deduction 2. Has correct form 3. Has nothing to do with truth
The two general fallacies
1. Mere assertion 2. Non-sequitur
Valid: if... Then...
1. Modus Ponens (affirms by affirming) 2. Modus Tullens (The way that denies by denying 3. Hypothetical syllogism (chain argument)
1. If people are bipeds, then they walk on two legs. 2. People are bipeds. 3. Therefore, they walk on two legs.
A -> B A B Valid; sound; modus ponens
1. If Socrates was wise, then he lived a good life. 2. Socrates lived a good life. 3. Therefore, Socrates was wise.
A -> B B A Invalid; Unsound; Affirming the Consequent
1. If Bush is President, then a Republican is President. 2. A Republican is President. 3. Then Bush is President.
A -> B B A Invalid; Affirming the consequent
1. If the tortoise wins the race, the hare will not. 2. The tortoise does not win the race. 3. Therefore, the hare will win the race.
A -> B ~A B Invalid; Unsound; Denying the antecedent
1. If Socrates drank the hemlock, he died as a martyr. 2. He did not die as a martyr. 3. Therefore, Socrates did not drink the hemlock.
A -> B ~B ~A Valid; Unsound; Modus tollens
1. If Obama is the President, then Bieber is not the President. 2. Obama is the President. 3. Bieber is not the President.
A -> ~B A ~B Valid; Sound; modus ponens
If Salem is the capital of Oregon, then it is not the capital of California. 2. Salem is not the capital of California. 3. Therefore, it is the capital of Oregon.
A -> ~B ~B A Invalid; Unsound; affirming the consequent
1. If Salem is the capital of Oregon, then it is not the capital of California. 2. If Salem is not the capital of California, then Sacramento is the capital of California. 3. Therefore, if Salem is the capital of Oregon, then Sacramento is the capital of California.
A -> ~B ~B -> C A-> C Valid; Sound; Hypothetical syllogism
A v B
A or B; A or B or both; A unless B; either A or B;
Salem is either the capital of California or it is the capital of Oregon. 2. Salem is not the capital of California. 3. Therefore, it is the capital of Oregon.
A v. B ~A B Valid; Sound; Disjunctive syllogism
The sky is blue or it is green. 2. The sky is not blue. 3. Therefore, it is green.
A v. B ~A B Valid; unsound; disjunctive syllogism
And you can ignore whatever Freud said because he did cocaine.
AD HOMINEM ABUSIVE ATTACK
Don't trust the government; it is full of lousy lying politicians who only care about themselves.
AN APPEAL TO VESTED INTEREST, AN AD HOMINEM ABUSIVE ATTACK, OR A HASTY GENERALIZATION. IT'S CHOCK-FULL OF FALLACIES.
I saw that Jessica Simpson uses Proactiv, so it must be worth trying. She has really nice skin.
APPEAL TO CELEBRITY
The President said that the economy is in good shape, therefore it is in good shape.
APPEAL TO DUBIOUS AUTHORITY.
Without OnStar you will probably die because your car won't be able to call 911 if you're in a car crash
APPEAL TO FEAR
For distinguishing tastes, like yours.
APPEAL TO VANITY
Beggin the Question and circular reasoning
Arguer assumes the conclusion in one or more premises or reiterates one or more premise in his or her conclusion.
Emotional Appeals
Arguer preys upon the emotions of audience, rather than appealing to reason. a. Pity b. fear. c. Vanity (happiness) d. Guilt
Red Herring
Arguer tries to distract the attention of the audience by raising an irrelevant issue.
Poisoning the well
Arguer undercuts the credibility of an opponent so much that the audience will not believe the opponent ever tells the truth.
Equivocation
Arguer uses a key word in two or more different senses.
How do I know my dream was accurate? Because it was a clairvoyant dream!
CIRCULAR REASONING
Past-life memories experienced by children prove that past lives exist because the children could have no other source for their memories besides having lived in the past.
CIRCULAR REASONING
Hasty Generalization
Drawing a general conclusion from a sample that is biased or too small
Censorship should not be a bad word. It is necessary for society to have censorship. Where would we be without stop signs and seatbelt laws? That is healthy censorship. So, there is nothing wrong with censoring the lyrics in music.
EQUIVOCATION ON THE WORD 'CENSOR'
The end of a thing is perfection. Death is the end of life. Therefore, death is the perfection of life.
EQUIVOCATION ON THE WORD 'END.'
Denying the antecedent is a valid argument form. True or False
False
Deductive Argument
Formal, truth of evidence, truth of conclusion. "If, then"
People over the age of 65 tend to be awful drivers. Haven't you noticed that most times when you're behind an awful driver, it's a little old person with glasses and gray hair?
HASTY GENERALIZATION
Anteaters and aardvarks have long noses. Therefore, all animals with names beginning with 'a' have long noses.
HASTY GENERALIZATION.
A-> B
If A, then B; A only if B; B, if A; B provided that A; A is sufficient for B; B is necessary for A; A implies B
Affirm the disjunct
Invalid use of "or"
A -> B ~B ~A
Invalid; modus tollens Unsound
I'm not sure Jill's opinion really matters during this meeting; she has only worked here for two weeks.
LACK OF EXPERIENCE
Inductive Argument
Likely hypothesis
Argument? A plebian is a commoner.
NO
Argument? For a long time, Pluto was considered to be the ninth planet in the solar system. That is no longer the case
NO
Argument? I do not want to eat vegetables because I do not like how they taste.
NO
Argument? Please do not sit on that chair because it's very rickety. I am afraid you will get hurt.
NO
Argument? You should be more careful.
NO
Argument? You would be healthier if you ate more vegetables.
NO
Smith lied to her parents when she was caught red handed. So what makes you think she is telling the truth now?
POISONING THE WELL
It is foolish to talk about a national preventative health insurance program. It can easily be shown that there will always be people around with infirmities and health problems, no matter what program we have in place.
RED HERRING.
If we ban assault rifles, surely this will lead to the loss of our Second Amendment Rights.
SLIPPERY SLOPE
If we leave natural resources to the masses, they will pursue their interests rampantly without restraint and lead to the complete depletion of natural resources.
SLIPPERY SLOPE
Senator Jones says that we should not fund the attack submarine program. I disagree entirely. I can't understand why he wants to leave us defenseless like that.
STRAW MAN. JONES NEVER ARGUED THAT WE SHOULDN'T HAVE A DEFENSE BUDGET.
Disjunctive syllogism is a valid argument form. True or False
True
Modus Tollens is a valid argument form. True or False
True
Distinguished nutritionists believe that adding walnuts to your diet is beneficial no matter your current diet or exercise regime; therefore everyone should eat lots of walnuts.
UNSPECIFIED AUTHORITY
~A -> B ~A B
Valid; modus ponens unsound
Argument? Recycling is not cost effective. It actually causes our city to lose money. The process of recycling is quite expensive. Additionally, recycling interferes with an individual's right to choose whether or not to recycle. So, we should do away with the recycling program.
YES
Argument? Vegetables contain many vitamins, minerals, antioxidants and fiber. Therefore they are good for you and you should eat them.
YES
Argument? We need ethical standards because power, knowledge and information are not equally distributed among the population.
YES
Argument? Methane is more harmful than most people realize, so we should focus our efforts on composting rather than recycling.
YES
Ad hominem- guilt by association
a claim that a type of group membership invalidates the person's argument. It's because she's from the south.
Non Sequiter fallacy
an argument where the conclusion doesn't follow presieses. Ex. If you buy this model, your family will be safer.
Non-Sequitur
an argument where the conclusion doesn't follow the premises
Appeal to the few
arguer appeals to a small, select population
celebrity
arguer appeals to celebrities to make his or her case
Appeal to the masses
arguer appeals to popularity of 'sheer numbers'
Appeals to tradition- tradition
arguer appeals to traditions or length of tie something has been in place. ex. you can be assured of our expertise at the body shop, we have 100+ yrs. of expertise
Unspecified authority- unspecified
arguer appeals to vauge authorities such as 'scientists' or 'studies' without providing specifics. ex. no wonder pediatricians are recommending vicks vaporub.
Inappropriate authority- Dubious
arguer appeals to wrong kind of authority. President said the economy will be fine in six months.
Mere assertion
arguer asserts claim without support, treating a single claim as an argument. Ex. I think war is wrong.
Mere assertion Fallacy
arguer asserts claim without support, treating a single claim as an argument. ex. I think war is wrong
Ad hominem attacks
arguer attacks the person who made the original argument instead of the person's argument.
Ad hominem-lack of experience
arguer claims opponent doesn't have enough experience to make the argument
Ad hominem- Vested interest
arguer claims opponent has ulterior motives for making the argument. ex. Of course he wants higher salaries for his teachers, his wife is a teacher.
Ad hominem- Tu quoque
arguer claims opponent is doing what she has been accused of ex. you're accusing me of losing my things all the time? You spent 45 minutes looking for your keys yesterday.
Appeal to Novelty
arguer claims that because something is newer, it must be better
Appeal to ignorance
arguer claims that something is true or false because it hasn't been proven wrong
Appeals to inappropriate authority
arguer inappropriately uses an authority to foster an argument
Ad hominem-abusive
arguer irrelevantly insults another ex. you're a jerk
Straw man
arguer misrepresents an opponent's view. (play on words)
Appeals to force
arguer threatens a reader or listener
Oversimplified Cause
because one thing appeared to cause another, it is the only factor that caused it, but there's actually more to the story. ex. Columbine shootings were because of violence on tv
False Cause/ Post Hoc Ergo Propter Hoc
because one thing happened after another thing, it must have resulted because of it.
Slippery slope
claiming, without sufficient evidence, that a seemingly harmless aciton if taken, will lead to a disastrous outcome
Affirming the consequent is a valid argument form. true or false
false
Affirming the disjunct is a valid argument form. True or false
false
An argument can be invalid and sound. true or false
false
Denying the antecedent is a valid argument form. True or false
false
A -> B B A
invalid, affirming the consequent Unsound
A -> B ~A ~B
invalid; denying the antecedent Unsound
~A
is not true
False dilemma
posing a false choice when there are more options than what is presented
Identifying argument words
since, firstly, secondly, for, as, afterall, assuming that, follows from, as shown, indicated by
Identifying conclusion words
therefore, so, it follows that, consequently, hence, thus, suggest, demonstrates, proves, entails, implies
Any kind of fallacy renders an argument useless. True or false
true
Modus ponens is a valid argument form. true or false
true
A V B ~A B
valid, disjunctive syllogism Unsound
Argument by Analogy
whole argument revolves around proving something wrong
