Obstacles to critical thinking:
- Egocentrism – Inability to see things at others’ points of view. I want you to support me and tell
me that I’m right. I don’t want your rational analysis. Just support me no matter what. Adults
are more egocentric
- Ethnocentrism – Or sociocentrism. My society, my ethnic background, etc.
- Stereotyping – Although there is a cognitive compensity to do this.
- Fear / Psychological Defensiveness – fear of questioning the beliefs
- Dogmatism – This is faith. I can’t prove it but I accept it.
- Bigotry –
- Propaganda – usually distorted information
- Resistance to change –
- Unquestioned Loyalties –
- Blind obedience to authority –
- Mindless conformity –
- Willed Ignorance –
- Demagoguery – Take facts and spin them to your advantage not in a way that accurately reflects
the truth. Or to spin them reversely to oppose your opponent. To raise emotions, prejudice, and
ignorance in poorer and less-educated. Lecture 3:
In order to have an argument we need two related claims. One claim supports the other. The supporter
claim is premise. The supported is the conclusion. The process is inference. A claim is a statement that
can be true or false.
- Questions are not claims. Unless they’re rhetorical questions.
- An opinion is a claim
- Ought Imperative – something you ought to do. Making a claim about what you should or
should not do.
o You should not smoke!
1- Keep off the grass = a command
o Commands are things that we ought to do
2- Abraham Lincoln was the first president of the United States. = claim
3- If Sally calls, tell her I’m at the library. = request
4- Can’t you see that pornography demeans women? = a rhetorical question and a claim
5- Toby, never throw a pen at your sister! You could put an eye out! (said byToby’s mother)= ought
imperative. (you ought not throw a pen because you could put an eye out!)
6- Never raise your hands to your kids. It leaves your groin unprotected.(George Carlin)= ought
7- Why don’t we eat at El Grande Burrito tonight. I feel like Mexican.= a proposal
8- In batting practice you must make a point of leaving the bad pitches alone. You don’t want your
refl exes to get into bad habits. (Mickey Mantle) = ought imperative
9- Life changes when you least expect it to. The future is uncertain. So seize this day, seize this
moment, and make the most of it.( Jim Valvano, quoted in Mike Krzyzewski, Leading with the
Heart ) = ought imperative
10- Take care of a good name: for this shall continue with thee, more than a thousand treasures
precious and great. (Ecclesiasticus 41:15) = ought imperative
11- You want to be very careful about lying; otherwise you are nearly sure to get caught. (Mark
Twain, “Advice to Youth”)= ought imperative
12- Democracy has at least one merit, namely, that a member of Parliament cannot be stupider than
his constituents, for the more stupid he is, the more stupid they were to elect him. (Bertrand
Russell, Autobiography )= ought imperative (namely = let me explain) for is the key word
Does it contain an argument? (do they try to proof something or explain sth?
1- I’m trading in my Ford Explorer for a Toyota Corolla because they’re more reliable and get better
gas mileage. – No! It is an explanation
2- Dinosaurs became extinct sixty-fi ve million years ago, probably as a result of dramatic global
cooling that resulted from the impact of a large asteroid. – an explanation because it is widely
spread and accepted a. Explanations can be wrong. But they are not arguments. The passage does not argue but
3- Dogs make better pets than cats because they’re more intelligent and obedient. – an argument
4- The rich and famous tend not to be happy, well-adjusted personalities. Look at Britney Spears. –
5- I stayed home from school because I was sick. – explanation
Enthymemes – an implicit claim. An Argument containing unstated claims. (premise/conclusion)
- Implicit (not explicit) – assumed, understood but not stated.
- Missing claim is part of the argument and the argument can’t be properly understood without it.
An untold assumption that the whole argument is based on.
- Example: “The bigger the burger, the better the burger. The burgers are bigger at Burger King.”
The implicit statement (unstated conclusion) is: the burgers are better at Burger King.
- Through a series of claims, you will be led to an obvious conclusion which is actually missing.
- Example: Herman couldn’t be the robber. He didn’t have a tattoo on his left arm. Implicit: the
robber had a tattoo on his left arm.
Simple vs Complex Arguments:
Simple argument – an argument with one and only one conclusion and at least one supporting premise.
- Example1: She’s armed so she’s dangerous. (p1 = She’s armed. C = so, she’s dangerous.)
Standard form – main conclusion always goes at bottom. Supporting premise(s) always go above the
conclusion they’re meant to support.
Example2: in view of the fact that (Toronto Raptors traded away their best player), (they will not make
the NBA play-offs.)
Complex argument – arguments with more than one conclusion.
- There is one main conclusion and one an intermediate one.
- Each intermediate conclusion can be a claim to prove the main conclusion.
- Example: “Jesse breaks bones so easily and he dislocates his shoulder with every hard hit. So,
let’s face it, he’s too fragile. Because of this, we’re forced to conclude that Jesse will not make it
to the National Football League.”
o Premise One: Jesse breaks bones too easily
o Premise Two: He dislocates his shoulder with every hit. o Premise Three (and Conclusion1): He’s too fragile.
o Conclusion Two (main): Jesse will not make it to the National Football League.
o During the exam instead of numbers write full sentences for the standard form diagram.
- Linked and Joined Premises: “they work together, they depend each other”. If the first one is
irrelevant, the second is.
o “Contest winners will go to Florida. Michelle won the contest. She goes to Florida”. None
of the facts alone can’t state that Michelle goes to Florida. It’s the joint link between
two facts that infers that Michelle goes to Florida. Lecture 4:
Two kinds of Reasoning:
1- Non-deductive reasoning (inductive, non-formal) –
o Uses ordinary language
o Conclusions do not follow necessarily but probably
o Arguments are weaker or stronger by degree. Not either right or wrong.
2- Deductive reasoning (formal) –
o Form (structure) vs content (language, topic, substance)
o Valid logic. Always leads to a necessary conclusion. Either 100% valid or 100% invalid. Lecture 5 – Formal Deductive Logic
Valid forms of logic:
1, 2, 3 are hypothetical arguments. (Meaning that they involve if, then)
1) Modus Ponens – If P then Q. P = Antecedent Q = Consequent
- If it’s cold (P), I’ll wear a coat (Q). It’s cold (Affirmed the Antecedent), so I’ll wear a coat
- Invalid form of Modus Ponens – If P then Q. Q so P. (Affirming the consequent)
o If it’s a chair (P), it has 4 legs. It has 4 legs, so it’s a chair.
2) Modus Tollens – If P then Q. Not Q. So, Not P.
- If it’s winter, then it is cold. It is not cold, so it is not winter.
- If you are in Toronto, then you’re in Canada. You are not in Toronto. So, you are not in Canada.
- Invalid form of Modus Tollens – If P then Q. Not P. So, Not Q.
o If I’m in Toronto, then I’m in Canada. I’m not in Toronto. So, I’m not in Canada.
3) Chain Argument – If P then Q. If Q then R. Therefore, if P then R.
- If I study, then I’ll pass the test. If I pass the test, then I’ll pass the course. So, If I study, I’ll pass
- Invalid forms of Chain Argument:
a. Fallacy of Common Antecedent – If P then Q. If P then R. So, if Q then R.
i. If I smoke cigarettes, then I’ll be cool. If I smoke cigarettes, then I’ll get cancer. If
I’m cool, then I’ll get cancer.
b. Fallacy of Common Consequent – If P then R. If Q then R. So, If P, then Q.
c. Fallacy of the Reverse Conclusion – If P then Q. If Q then R. So, If R then P.
i. If I get AIDS, then I’ll die. If I die, then I’ll get buried. If I get buried, then I’ll get
4) Disjunctive Syllogism – Either A or B. Not A. So, B.
a. I’m either alive or dead. I’m not dead. So, I must be alive.
b. A is called a disjunct and B is called a disjunct.
c. Invalid form – Either A or B. A, so not B. (affirming the “inclusive” disjunct.)
i. Either I’m a man (A) or I’m Canadian (B). I’m a man. So, I can’t be Canadian.
5) Categorical Syllogism – All A is B. C is A. C is B.
a. All men (A) are mortal (B). Socrates (C) is a man (A). So, Socrates (B) is mortal (B).
i. Major Premise (major premise) – All men are mortal
ii. Minor Premise (factual premise)– Socrates is a man
iii. Conclusion – Socrates is mortal
b. We talk about categories. All of something, some of something, none of something.
c. Invalid Form –
6) Practical Syllogism – a. Hurting people (S) is wrong(P). Gossiping (Q) is hurting people(S). So gossiping (Q) is
You’re violating the norms of rational thought. STOP!
Non-formal, non-deductive logic.
Evaluating deductive arguments
Validity – refers to structure/form of an argument
- 100% valid or nvalid
- Point or claims are not valid or invalid. It’s the structure (form) of an argument that can be valid
- Planets are made of cheese; earth is a planet so it’s made of cheese. (valid argument)
- Necessary: only one possible conclusion
Truth – refers to claims. They are ether true or false.
- Determines the “acceptability of claims”.
- Valid arguments can contain false claims.
Soundness – an evaluative criterion encompassing both validity and truth.
- A sound argument is valid in logical structure and contains true claims.
- The conclusion of a sound argument is necessarily true.
Exercise 3.2: (test case)
1- “If we’re in Los Angeles, then we are in the United States. We are in the United States. So, we
are in Los Angeles.”
a. *If we’re in Los Angeles+ (P), *then we are in the United States.+ (Q) *We are in the
United States.] (Q) [So, we are in Los Angeles.] (P) b. Invalid argument.
c. Name: affirming the consequent.
2- “If we’re in United States, then we are on earth. We are in United
States. So, we are on earth.”
a. *If we’re in United States+, (P) [then we are on earth.] (Q) [We are in United States.] (P)
[So, we are on earth.] (Q)
c. Modus ponens
d. Valid argument.
3- “Some students sell back this textbook at the end of the semester. So, it is likely that all students sell
back most of their textbooks at the end of the semester.”
- Weak arguments. How could you improve “some students” to “all students”?
- What do you mean by some? That’s vague!
5- “Many of the children in Ms. Santuzzi’s first-grade class can read. So, most children in the first grade
- Weak argument.
- “Many” is not necessarily the majority.
- Maybe she’s teaching a gifted class.
6- “Many of the unemployed steelworkers who hang out at the Dew Drop Inn are actively looking for
work. So, it must be that many unemployed steelworkers are actively looking for work.”
8- None of the many students Lisa knows at State College are majoring in anthropology. So, it may be
that not many students at State are majoring in anthropology.
Types of Claims:
1- Empirical Claims – factual claims (can be true or false in principal).
a. Descriptive. Describe about what is true, or what will be true, or what was true.
b. Empirical claims require verification through:
i. Sensory observation
ii. Correlational studies
iii. Past experience
iv. Expert testimony 2- Normative Claims – value-related (value-judgement) + ought imperatives
a. Value judgement: good/evil, right/wrong, praise/blame.
b. E.g.: Abortion is wrong.
i. Your authorities are only on people who share the same faith with you.
ii. Hitler was evil.
c. They require justification based on rational appeals and not authorities. Rational
appeals are principals:
ii. Respect for persons
iii. Freedom (Higher-order value)
iv. Happiness (Higher-order value)
v. Equality (Higher-order value)
3- Conceptual / Mixed Claims – involve matters of definition and meaning. Comparing concepts.
a. When you’re forced to ask questions. What do you mean by … ?
i. E.g.: Do you know war is pornographic? They’re both disgusting. (depends on
what you mean by pornographic).
ii. E.g.: Does God exist? (what do you mean by God?)
b. They require linguistic analysis.
i. The fetus is a person. (we need the criteria of personhood)
ii. Money can’t buy happiness (what do you mean by happiness)
iii. Human actions are not free
iv. Fair treatment is identical treatment
v. Religion and ethics are the same.
d. Solve conceptual questions on test: Verification, justification, analysis.
Practical syllogism (usually used for value analysis)
Lying out of self-interest is committing a wrong doing. Joe is lying out of self-interest. So, Joe is
committing a wrong doing.
4 tests to determine the acceptability of a value premise:
1- Role-exchange test – would you be prepared to take that and accept the negativity of that
principal? a. Take the principal, apply it to yourself as the one most negatively affected. If you refuse
to have it applied to you, you’re not justified in applying it to others.
i. If I lie to you out of self-interest, would you be happy?
2- New cases – take the principal used in one case and apply it to other similar cases. See whether
the principal holds up. If not, principal fails this test.
a. E.g.: Lying is always wrong. Truth is a high value but there are higher values such as life.
So giving up the truth to save life is right.
3- Consistency and Universalizability – what would be the universal implications if everyone has
a. E.g.: everybody but me should pay their income tax. When it is universalized, nobody
will pay their income tax. (Greece)
b. E.g.: making a promise with the intention of breaking it = inconsistency.
4- Higher-order principal – You justify a specific moral rule or moral statement by appealing to a
broader or higher statement.
a. e.g.: shouldn’t throw stones out of windows. You will damage people’s property. It is
violating the higher-order principal or respecting other people’s property rights.
b. E.g.: You should give her one more candy. Why? That would be fair. Appealing to higher-
order principal of fairness. Lecture ?
In non-deductive reasoning, there are degrees of being good and bad. No argument is entirely good or
Informal Logical Fallacies:
1. Fallacies of relevance – Introducing things that are irrelevant to the argument.
i. Personal Attack Fallacies:
o Abusive Personal Attack (Ad Hominem) – rejecting a claim/argument by attacking the
character of the person making it. But the attack is irrelevant to the acceptability of the
o Attacking the Motive (Circumstantial Ad Hominem) – rejecting a person’s
claim/argument because of the motive. (Example: a person making the claim may
benefit if you accept it. It is in the interest of the person that you accept it.)
o Look who’s talking – rejecting an claim/argument because the person doesn’t practice
what they preach
o Genetic fallacy – rejecting an argument simply due to the source
o Poisoning the well – attacking somebody’s credibility. Not giving the person a way out.
ii. Two wrongs fallacy – trying to justify one act of wrongdoing by pointing to other similar
wrongdoings that went unpunished. But, this is irrelevant to the acceptability of the
iii. Inappropriate appeals to emotion:
o Scare tactics – A listener/reader/critic of a claim/argument is threatened to be harmed
if a claim or argument is not accepted. But, the threat is irrelevant to the acceptability
of the claim/argument.
o Appeals to pity – pulling on the heartstrings of someone to get them to accept your
o Bandwagon argument – accepting or rejecting a claim/argument because it’s either
cool or uncool. Coolness or uncoolness is irrelevant to acceptability of a claim.
o Straw man – The straw man fallacy is committed when an arguer distorts an
opponent’s argument or claim to make it easier to attack.
o Red herring – when an arguer tries to sidetrack his audience by raising an irrelevant
issue and then claims that the original issue has effectively been settled by the
E.g.: Many people criticize Thomas Jefferson for being an owner of slaves. But Jefferson was
one of our greatest presidents, and his Declaration of Independence is one of the most
eloquent pleas for freedom and democracy ever written. Clearly, these criticisms are
2. Fallacies of insufficient evidence – There is not enough support to warrant the conclusion
3. Fallacies of presumption – Presuming something that you ought not to presume
i. Begging the question:
o A because B where B = A o Circular reasoning
o The supporting premise is more problematic than the conclusion
ii. Equivocation – using one word in two different ways.
o E.g.: It is a crime to smoke grass. Kentucky bluegrass is a grass. Therefore, it is acrime to
smoke Kentucky bluegrass.
4. Fallacies of ambiguity – Problems with language.
i. A word could have multiple meaning, too broad, vague, etc.
ii. We can get different meanings with stressing on different words
5. Fallacies of diversion – changing the subject to divert attention
6. Inappropriate appeals to an emotion – using feelings to manipulate to accept some argument or
Fallacies of Insufficient Evidence:
- Inappropriate appeal to authority –
o traditional wisdom
o elite few
o one (e.g.: pope, dictator, president)
- Appeal to ignorance – something must be true because you haven’t proven it false. Or vice
- False alternatives – an arguer poses a false either/or choice.
- Loaded question – a claim is embedded in the question. The claim is problematic.
- Questionable cause –
o Post hoc – mere coincidence/superstition. (from the Latin post hoc ergo propter hoc
*“after this, therefore because of this”+) is committed when an arguer assumes, without
adequate evidence, that because one event, A, occurred before another event, B, A is
the cause of B.
o Mere correlation – when an arguer assumes, without sufficient evidence, that because
A and B regularly occur together, A must be the cause of B or vice versa.
o Oversimplified cause – when we assume, without adequate evidence, that A is the sole
cause of B when, in fact, there are several causes of B.
- Hasty generalization – statement that asserts that all or most things of a certain kind have a
certain quality or characteristic.
- Slippery slope – We often hear arguments of this sort: “We can’t allow A, because A will lead to
B, and B will lead to C, and we sure as heck don’t want C!” Arguments of this sort are called
slippery-slope arguments. Often, such arguments are fallacious. We commit the slippery-slope
fallacy when we claim, without sufficient evidence that a seemingly harmless action, if taken,
will lead to a disastrous outcome. Then the outcome is used to reject the argument. (A)
- Weak analogy – an arguer compares two (or more) things that aren’t really comparable in
relevant respects. - Inconsistency – Two statements are inconsistent when they both can’t be true. The fallacy of
inconsistency occurs when an arguer asserts inconsistent or contradictory claims.
Pg 155 – 6.1
- “I can’t believe I failed my chemistry test. I knew I should have worn my lucky sweatshirt to take
o Fallacy of questionable cause. Post hoc. (1 mark for fallacy, .5 mark for questionable
cause, .5 mark for post hoc)
- “Did you vote for the idiot or the liar in the last presidential election?”
o Fallacy of loaded question.
- “Skeptics have tried for centuries to prove that reincarnation is a myth, and no one has ever
succeeded. Therefore, we must conclude that reincarnation is a fact.”
o Fallacy of appeal to ignorance.
- “I’ve long been convinced that nothing exists outside my own mind. Indeed, the arguments for
this seem so obvious to me that I can’t understand why everybody else doesn’t believe it, too.”
o Fallacy of inconsistency. If we accept the first argument (nothing exists outside my
mind) then, there would be no “everybody else” to believe it or not.
- Police detective: Did you get a good look at the bank robber? Witness: Yes, I saw his face clearly.
It was Willie, the night watchman. Detective: And were you also able to recognize his voice?
Witness: No, I couldn’t really hear what he said very well. His voice was muffled by the full ski
mask he wore.
- Either you support preferential treatment for disadvantaged minorities in university admissions,
or you’re a racist. But surely you’re not a racist. Therefore, you support preferential treatment
for disadvantaged minorities in university admissions.
o Fallacy of false alternatives.
- Students have asked that we extend residence hall visitation hours by one hour on Friday and
Saturday nights. This request will have to be denied. If we give students an extra visitation hour
on weekends, next they’ll be asking us to allow their boyfriends and girlfriends to stay over all
night. Eventually, we’ll have students shacking up in every room.
o Fallacy of slippery slope
- There is no information in Private Baker’s service record that indicates that he is not a
homosexual. Consequently, I can only assume that he is.
o Fallacy of appeal to ignorance
- I’ve searched my car carefully, and I haven’t found my lost car keys there. It’s reasonable to
conclude, therefore, that my car keys aren’t in the car.
o No fallacy
- You’re not seriously thinking of voting for that bum, are you? Why don’t you wake up and smell
o D - Why all the fuss about preserving old-growth redwood forests? Redwood trees are like Motel
6’s. Once you’ve seen one, you’ve seen them all.
o Fallacy of weak analogy. Comparing two things that are similar in some aspects. So they
are similar in more aspects.
- The volcano erupted shortly after the king abandoned worship of the ancient tribal spirits. The
tribal spirits must be angry.
o Fallacy of post hoc.
- If a large asteroid had struck China in AD 1200, it’s likely that some historical records of the
disaster would have been preserved. But there is absolutely no mention of any such catastrophe
in any of the numerous Chinese historical records that survive from that period. Therefore, it’s
reasonable to conclude that a large asteroid did not strike China in AD 1200.
o No Fallacy
- Why do you find it so difficult to be fair and impartial?
o Fallacy of loaded question.
- Since the 1960s promiscuity, divorce, abortion, teen suicide, and out-of wedlock births have all
risen sharply. Clearly, we need to restore prayer in public schools.
o Fallacy of oversimplified cause
- A benevolent, all-powerful Creator may exist. On the other hand, a benevolent, all-powerful
Creator may not exist. No one knows for certain which of these claims is true. But one thing is
certain: one of these claims must be true.
o Fallacy of false alternatives. There may be two Gods.
Fallacies of ambiguity
1- Equivocation – an ambiguity caused by a shift between two legitimate meanings of the term.
a. e.g.: if you believe in the miracles of the science then, you should also believe in the
miracles of bible.
2- Amphiboly – an ambiguity caused by faulty sentence structure. (the fallacy involves the whole
sentence, not one word)
a. e.g.: I voted for the independent candidate with the highest hopes.
3- Fallacy of accent – a statement that is ambiguous because its intended tone of voice is
uncertain. Secondly, its stress is unclear. Or third, it is quoted out of context.
a. E.g.: I will be taking the best philosophy course in September
b. If stress is on “I” = who
c. If stress is on “will” = whether
d. If stress is on “best” = quality of course
e. If stress is on “philosophy” = which course
f. If stress is on “in September” = when
4- Reification / hypostatization – treating abstract terms like concrete ones or ascribing human-
like properties to them. a. E.g.: even when he was home, the job would call to him seductively asserting its
dominance, luring him back to its embrace.
5- Fallacy of Division – the false assumption of what is true of the whole or group, must be true of
the individual members.
a. E.g.: this is the richest sorority on campus. Mary is a member so, she must be one of the
richest on campus
b. E.g.: Most rich people of Canada live in Oakville. Tony lives in the Oakville so he’s one