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Ryerson University

Social Sciences and Humanities

SSH 105

Catherine Ellis

Winter

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Critical Thinking – CHAPTERS 1,2,3,4,5,6 STUDY GUIDE
CHAPTER 1:
What is Critical Thinking?
- The systematic evaluation or formulation of beliefs, or statements, by rational standards.
- It’s systematic because it involves distinct procedures and methods (not just gut feelings).
- It’s used to evaluate existing beliefs and formulate new ones.
- It evaluates beliefs in terms of how well they are supported by reasons.
Assertion (Statement):
- An assertion is a declarative sentence that is intended to make a claim of some sort. (Ex. I have
3 coins in my pocket.)
- Sometimes these are called statements or propositions.
“I am taller than you.”
“It is raining.”
“She will win the race.”
- Assertion can be true or false.
Premise:
- A premise is a statement that is offered in support of a conclusion.
Conclusion:
- A conclusion is a statement that is held to be supported by a premise or premises.
- Example:
Premise: All whales are mammals.
Premise: Moby Dick is a whale.
_____________________
Conclusion: Moby Dick is a mammal.
Argument:
- An argument is a set of statements one of which (the conclusion) is taken to be supported by
the remaining statements (the premises).
- Here’s another way of saying this:
An argument is a group of statements in which some (the premises) are intended to support another
(the conclusion).
The conclusion is what the speaker wants you to accept.
The premises state the reasons or evidence for accepting the conclusion.
Inference:
- An inference is the move from a premise (or premises) to a conclusion (or conclusions).
- Critical thinking is all about inferences
- Inferences are identified and evaluated
Don’t confuse arguments with explanations.
- An explanation tells you why something happened.
- An argument tells you why you should believe something.
- Arguments have something to prove; explanations do not. Example:
1) Adam stole the money, for three people saw him do it. (Argument)
2) Adam stole the money because he needed to buy food. (Explanantion)
Be aware that NOT all series of statements contain arguments.
- So how do we recognize arguments?
- Look for a conclusion (a statement that is being supported), and look for premises.
- Often we can identify these by the use of certain indicator words
Conclusion-Indicators
- Thus
- Therefore
- Hence
- Entail(s)
- … it follows that …
- … we may conclude …
- Consequently
- So
Premise-Indicators
- Since
- Because
- For
- As
- … given that …
- … inasmuch as …
- … for the reason that …
Two Points about Indicator words:
- First: They may not actually be present in arguments.
- Second: In arguments, premises do not always come before conclusions; conclusions do not
always come after premises
“textual priority versus logical priority”:
- “Religious beliefs cannot be proven. If something is a matter of faith, it cannot be proven, and
religious beliefs are obviously a matter of faith.”
Truth versus Logical Strength:
- Premises and conclusions may be true, or they may be false.
- Evaluating the truth-value of premises and conclusions is distinct from evaluating the logical
strength of arguments. 1) Ryerson University is in Guelph, ON.
2) The RAC is located within Ryerson U.
___________________________
Therefore,
3) The RAC is located in Guelph, ON.
Deductive Arguments
- A deductive argument is intended to provide conclusive support for its conclusion.
- A deductive argument that succeeds in providing conclusive support for its conclusion is said to
be valid.
- One that fails to provide conclusive support is said to be invalid.
- A valid argument is such that if its premises are true, then its conclusion must be true.
- For this reason, deductively valid arguments are said to be truth-preserving.
- An argument is deductively valid if and only if it is not possible for the premises to be true and
the conclusion false.
- i.e., if all the premises were true, the conclusion would have to be true too.
- An argument is deductively invalid if and only if it is not deductively valid.
Validity and Soundness:
Deductive Validity:
A deductively valid argument:
(1) All bachelors are unmarried.
(2) Ivan is a bachelor.
____________________________
Therefore,
(3) Ivan is unmarried.
An invalid argument:
(1) Some politicians smoke marijuana.
(2) Jones is a politician.
__________________________
Therefore,
(3) Jones smokes marijuana.
Remember, a valid argument need not have true premises, and it need not have true conclusions:
what’s important is the logical relationship between the premise(s) and conclusion(s).
(1) All Americans are ten feet tall.
(2) Prof. Hunter is an American .
Therefore,
(3) Prof. Hunter is ten feet tall - Not all deductively valid arguments have true premises and true conclusions.
- In fact, a valid argument may have any of the following combinations:
(These are all VALID ARGUMENTS)
1) False Premises, False Conclusion
(1) All human beings can fly.
(2) All things which can fly are red.
(3) Therefore, All human beings are red.
2) False Premises, True Conclusion
(1) All dogs are reptiles.
(2) All reptiles are mammals.
(3) Therefore, All dogs are mammals.
3) True Premises, True Conclusion
(1) If you’re taller than 10 feet, you’re taller than 5 feet.
(2) If you’re taller than 5 feet, you’re taller than 2 feet.
(3) Therefore, If you’re taller than 10 feet, you’re taller than 2 feet.
- The only combination a valid argument may not have is true premises and false conclusion.
- A deductively valid argument with true premises is said to be sound.
Deductive Soundness:
- An argument is deductively sound if and only if it is deductively valid and all its premises are
true.
Deductive Versus Inductive Arguments:
- In a deductively-valid argument, the truth of the premise(s) guarantees the truth of the
conclusion(s). But, not all arguments are deductive:
- Inductive Strength:
An argument is inductively strong if and only if the conclusion is probably true, given
the premises.
An argument is inductively weak if and only if it is not inductively strong.
Inductive Strength: An argument is inductively strong if and only if the confusions is probably true, given
the premises.
Inductively Strong Argument:
(1) Quitting smoking usually improves your health.
(2) Mary has quit smoking.
Therefore, probably
(3) Mary’s health will improve. Inductively Weak Argument:
(1) A few police officers are corrupt.
(2) Jim is a police officer.
Therefore, probably,
(3) Jim is corrupt.
CHAPTER 2:
- Impediments to critical thinking classified
Common impediments to critical thinking:
Category 1: hindrances that arise because of how we think.
Category 2: hindrances that occur because of what we think.
Category 1 Impediments to Critical Thinking:
(a) Self-Interested thinking:
- Accepting a claim solely on the grounds that it advances, or coincides with, our interests.
- Overcoming self-interested thinking:
Watch out when things get very personal.
Be alert to ways that critical thinking can be undermined (ex: wishful thinking).
Ensure that nothing has been left out:
o Avoid selective attention.
o Look for opposing evidence.
(b) Group Thinking:
- Peer pressure Fallacy: an argument form that is both common and defective.
Fallacy of appeal to popularity
Fallacy of appeal to common practice
Fallacy of appeal to tradition
Genetic fallacy
- Stereotyping:
Drawing conclusions about people or groups without sufficient reasons.
Some Terminology Concerning Knowledge.
- Different uses of “knowledge”:
Knowledge by acquaintance
Knowledge-how
Propositional knowledge (knowledge-that)
- Three key ingredients in propositional knowledge:
Belief
Truth
Justification
Category 2 Impediments to Critical Thinking
(a) Subjectivism:
- The view that propositions have no truth-value (i.e. they are neither true nor false).
e.g.: Moral subjectivism: the view that moral claims have no truth-value.
(b) Relativism:
- The view that propositions have a truth-value, but that what this is depends upon (i.e. is relative
to) some person or social group.
i) Subjective Relativism:
- The view that the truth-value of a proposition depends solely upon (is relative to) what some
subject believes.
“that’s true for you “
“that’s my truth”
Objections:
(a) This is implausible: consider the jar of jelly beans
(b) This view would make us infallible
(c) This view is self-defeating (i.e. if it’s true, then it is an example of a truth that is not relative)
ii) Social Relativism:
- The view that the truth-value of a proposition depends solely upon (is relative to) societies.
Objections:
(a) Implausible
(b) Intolerant views
(c) Would make societies infallible
(c) Self-defeating (c) Philosophical Skepticism:
- The view that propositions have truth-values, but that we know what very few, or none, of them
are. (In other words, we know a lot less than we think or nothing at all.)
Consider the following argument for skepticism:
Objections:
(a) Requiring absolute certainty for a belief to count as knowledge is asking too much.
CHAPTER 3:
Deductive Argument Patterns
- There are some common patterns shared by many deductive arguments.
- They form a frame that is common to many arguments.
- Understanding some basic argument patterns helps to determine (a) whether an argument is
deductive and (b) whether it is valid or invalid.
- Many of these patterns involve two kinds of statements:
Conditionals & Disjunctions
Conditional Statements
- A conditional statement is a statement of the form
If p, then q.
- Examples:
If it rains, then the picnic will be cancelled.
If Jones didn’t commit the murder, the butler did.
- Conditionals are compound statements composed of two parts:
The antecendent – what follows the word “if”
The consequent – what follows the word “then” Conditional Statements and Necessary Conditions vs. Sufficient Conditions
- “A is a necessary condition for B”, means “without A, B would not be true.”
- “A is a sufficient condition for B”, means “If A is true, then B would have to be true as well.”
(e.g.) If John is a bachelor, then John is unmarried.
The consequent – “John is unmarried”
- Expresses a necessary condition for its being true that John is a bachelor; if it was false, then
he could not possibly be a bachelor.
- But being unmarried is not sufficient for being a bachelor. One must also be male.
The antecedent– “John is a bachelor”
- Expresses a sufficient condition for its being true that John is a unmarried; if it is true that John
is a bachelor, then it would have to be true that he is unmarried.
- But being a bachelor is not a necessary condition for being unmarried. Women are often
unmarried, although they are never bachelors.
o The antecedent of a conditional statement expresses a sufficient condition for the consequent.
o The consequent of a conditional statement expresses a necessary condition for the
antecedent.
Disjunctive Statements
- A disjunctive statement is a statement of the form
Either p or q.
- Examples:
Either the picnic was cancelled or it rained.
Either Jones committed the murder or the butler did.
- Disjunctions are compound statements composed of two parts called the disjuncts.
Some VALID conditional argument patterns
1) Affirming the antecedent (Modus Ponens):
If p, then q.
p.
Therefore, q.
- Example:
(1) If the Conservatives won the election, then Stephen Harper is the new Prime
Minister.
(2) The Conservatives won the election.
______________________________________________
Therefore,
(3) Stephen Harper is the new Prime Minister. (From premise (1) and premise (2) by
Modus Ponens) 2) Denying the consequent (Modus Tollens)
If p, then q.
Not q.
Therefore, not p.
- Example:
(1) If the Liberals won the election, then Paul Martin is the new Prime Minister.
(2) Paul Martin is not the new Prime Minister.
________________________________________________
Therefore,
(3) The Liberals did not win the election. (From premise (1) and premise (2) by Modus
Tollens)
3) Hypothetical Syllogism
If p, then q.
If q, then r.
Therefore, if p, then r.
- Example:
(1) If the Conservatives won the election, then Stephen Harper is the new Prime
Minister .
(2) If Stephen Harper is the new Prime Minister, then someone from Alberta is the new
Prime Minister.
______________________________________________
Therefore,
(3) If the Conservatives won the election, then someone from Alberta is the new Prime
Minister. (From premise (1) and premise (2) by Hypothetical Syllogism)
Some INVALID conditional argument patterns
4) Denying the Antecedent
If p, then q.
Not p.
Therefore, not q.
- Example:
(1) If Einstein invented the computer, then he’s a genius.
(2) Einstein did not invent the computer.
_____________________________________
Therefore,
(3) He’s not a genius. (From premise (1) and premise (2) by ???) 5) Affirming the Consequent
If p, then q.
q.
Therefore, p.
- Example:
(1) If Einstein invented the computer, then he’s a genius. (Expresses a sufficient
condition)
(2) Einstein is a genius.
_____________________________________
Therefore,
(3) He invented the computer. (From premise (1) and premise (2) by ???)
• The antecedent expresses a sufficient condition for the consequent. (FOR QUIZ 3)
• The consequent expresses a necessary condition for the antecedent. (FOR QUIZ 3)
A VALID disjunctive argument pattern
6) Disjunctive Syllogisms
(i) Either p or q.
Not p.
Therefore, q.
(ii) Either p or q.
Not q.
Therefore, p.
Example:
(1) Either the Liberals won or the Conservatives did.
(2) The Liberals did not win.
_______________________________________
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