Critical Thinking

PHILOS 2CT3

Valid Conditional Argument Forms

Affirming the antecendent

denying the consequent

hypothetical syllogisms

disjunctive syllogism 

conditional statement

“if - then” statement

antecendent

first statement (if part)

consequent

second statement (then part)

affirming the antecedent

modus ponens

• if p, then q

• p. therefore, q

p implies q

denying the consequent

modus tollens

• if p, then q

• not q. therefore, not q

hypothetical syllogisms

• if p, then q

• if q, then r

• therefore, if p, then r

3 statements → 2 premises & 1 conclusion

disjunctive syllogism

• either p or q

• not p. therefore, q

either disjunct (parts separated by “or”) can be denied

invalid conditional argument forms

denying the antecedent

affirming the consequent

denying the antecedent 

• if p, then q

• not p

• therefore, not q

denying p doesn’t mean q can’t happen other ways

affirming the consequent

• if p, then q

• q. therefore, p

p implies q

→ doesn’t say anything about what q implies

independent premise

doesn’t depend on other premise to support conclusion

if removed, support that other premise’s give to conclusion isn’t affected

dependent premise

depends on at least one other premise to provide joint support to conclusion

if removed the support the linked premise provides to conclusion is undermined

underlined in diagram

statement

assertion that something is or is not the case (asserting the way the world is)

reasons

provide support for statement

argument

group of statements in which some of them (premises) are intended to support another of them (conclusion)

premise

statement/reason given in support of the conclusion

conclusions

the statement the premises are intended to support

inferences

the mental process of reasoning from the premise/ premises to a conclusion based on those premises

indicator words

words that frequently accompany arguments and signal that a premise/ conclusion is present

premise indicators

because, in view of the fact, since, as indicated by, given that

conclusion indicators

therefore, so, consequently, which means that, as a result

Critical Thinking

the systemic evaluation or formulation of beliefs or statements

barriers of critical thinking

because of how we think

because of what we think

because of HOW we think

• accepting a claim solely bc it furthers your interest

• epistemic partiality

  • believing smth determined by considerations that arise from friendship

• ex: if from objective perspective your friend is guilty but they say they didn’t do it

• peer pressure

• appeal to popularity

peer pressure

group pressure to accept/ reject a claim solely on basis of what one’s peers think / do

because of WHAT we think

• subjective relativism

• social relativism

social relativism

truth is relative to societies (instead of individuals)

ex: our society believes sky is blue today so it is.

argument forms

deductive

inductive

deductive argument

intended to provide logically conclusive support for conclusion

• valid deductive arguments are truth-preserving  because the truth of the conclusion is guaranteed if the premises are true

valid deductive argument

if premises are true, conclusion must be true

• the conclusion follows logically from premises

ex: all humans are mortal. socrates is human. therefore, socrates is mortal

can have:

• false premise, false conclusion

• false premises, true conclusion

• true premises, true conclusion

can’t have:

• true premises, false conclusion

  • bc deduction requires true conclusion based on premise

invalid deductive argument

the conclusion does not follow logically from premises

ex: if socrates has horns, he is mortal. socrates is mortal. therefore, socrates has horns.

can have a true conclusion but the argument is invalid bc there is no support from premises offered

inductive argument

premises intended to provide probable not conclusive support for its conclusion

• not truth-preserving bc truth of conclusion isn’t guaranteed by truth of premises

• can be strong: conclusion is rendered probable and worthy of acceptance

ex: almost all humans are mortal. socrates is human. therefore, socrates is probably mortal

difference between deductive & inductive

• deductive provide obsolete conclusion (either true of false)

• inductive provide conclusions that can vary from very weak to extremely strong

Sound Argument

deductively valid argument with true premises. 

cogent argument

strong inductive argument with all true premises

• good inductive arguments are cogent

• bad inductive arguments are not cogent

Fallacies

• Genetic fallacy

• Appeal to the person

• Composition

• Division

• Equivocation

• Appeal to popularity

• Appeal to tradition

• Appeal to ignorance

• Appeal to emotion

• Red herring

• Straw man

Genetic Fallacy

arguing a claim is true / false solely because of its origin (who/where it comes from)

• can be relevant factor (e.g., expert witness in courtroom)

ex: Russel’s idea about tax hikes came to him in a dream, so it must be silly

Appeal to the Person

rejecting a claim by criticizing the person who makes it rather than the claim itself

• special case of genetic fallacy sometimes call ad hominem attack — an insult

• unless we can show how a person’s faults translate into faults in claim 

• ex: famous philosopher Martin Heidegger was a Nazi party member, so we can’t take his philosophy seriously —> must show Nazi ideas implicated within philosophy

ex: we should reject Chen’s argument for life on other planets. he relies on fortune-tellers for financial advice

1. circumstantial

2. hypocrisy

3. poisoning the well

1. Circumstantial

(based on circumstance)

someone deduces a claim as false because the person making it, given their circumstances, would be expected to make it

ex: Madison says she’s in favour of higher levels of immigration, but you can’t take her seriously. That view goes against everything her whole family believes

2. Hypocrisy

Tu quoque

Ex: “Ellen claims X, but doesn’t practise/ live by/ condone X by herself - so X is false”

• whether someone is hypocritical about their claims can have no bearing on the truth of those claims

• their views must stand/ fall on their own merits

3. Poisoning the Well

ex: “X has no regard for the truth or has non-rational motives for espousing a claim, so nothing that X says should be believed - including the claim in question/ possibly any claim in the future

• fact that someone has dubious reasons for making a claim doesn’t make it false, no mean everything that comes from them can be automatically dismissed 

pre-emptive attack person & dismiss their argument — could be true but may have no relation between information & claims being made

Difference Between Ad Hominems & Genetic Fallacy

• AH dismiss claims while GF offers origin in favour of claim

• AH are dialectical fallacy’s - always involve another person

• GF is in air of actual argument - doesn’t make appeal to another person

Composition

arguing what is true of the parts must be true of the whole

• not always fallacious (e.g., since all parts of house are made of wood, house itself is made of wood)

sometimes the whole doesn’t share same properties as parts

ex: “atoms that make up human body are invisible. Therefore, the human body is invisible.”

Division

arguing that what is true of the whole must be true of the parts

ex: “a university degree is a valuable thing to have! so how can you possibly think that this course in underwater basket weaving isn’t valubale”

Equivocation

using a word in two different senses in an argument

• the word has one meaning in one premise and another meaning in another

Appeal to Popularity

arguing a claim must be true merely because a substantial number of people believe it

• what many other ppl believe can be an indication of truth if they are experts/ have expert knowledge in issue at hand

appeal to common practice

• argument about what many ppl do

ex: “Most people approve of the provincial government’s decision not to pay for in vitro fertilization treatment. So I guess that decision must be a good one.”

Appeal to Tradition

Arguing a claim must be true just because its part of a tradition

ex:  “acupuncture has been used for a thousand years in China. It must work.”

Appeal to Ignorance

arguing that a lack of evidence proves something

• think claim is true bc not proven false

ex: “it’s clear that God exists because science hasn’t proved that he doesn’t exist.”

burden of proof: weight of evidence of argument required by one side in debate/disagreement

Appeal to Emotion

use of emotion in place of relevant reasons as premises in argument

• appeals to ppls guilt, anger, pity, fear, compassion, resentment, pride

• but not good reasons that logically support your case

Red Herring

Deliberately raising irrelevant issue during and argument

• subtle change of subject

Straw Man

Distorting, weakening, or oversimplifying someone’s position so it can be more easily attacked / refuted

general form:

• reinterpret claim X as weak/ absurd claim Y

  • Attack claim Y

    • Conclude X is unfounded