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PHI1101- Test #2.docx

Course Code
PHI 1101
Laura Byrne
Study Guide

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PHI1101- Test #2
Critical Thinking
Deductively Valid Argument Forms
Modus Ponens
If p (Antecedent) then q (Consequent). p. Therefore, q.
“If, then” statements.
Affirming the Antecedent. (first condition)
Ex. If you live in Montreal, then you life in Quebec. You live in Montreal.
Therefore, you live in Quebec.
Modus Tollens
If p then q. ~q. Therefore, ~p.
Ex. If you live in Montreal, then you live in Quebec. You do not live in Quebec.
Therefore, you do not live in Montreal.
Denying the Antecedent. (second condition)
If the antecedent is true, the consequent will be true.
Clarifying Meaning
The Principle of Charity
Adopting the most charitable interpretation of your opponent’s words when there
are two or more possible interpretations.
Lacking a precise meaning  unable to tell if it is true or false.
Not that they lack a precise meaning but that they have two or more precise
 Two main types of Ambiguity
Semantic Ambiguity
A word or phrase with multiple meanings.
Two Types of Semantic Ambiguity
Distributive is referring to each and every member.
Collective is referring to the whole class.
Ex. Statistics show that Canadians have 2 ½ kids Collectively makes sense,
distributive does not.
Use and Mention
Use: Using a word in its normal function to refer to something else.
Ex. The dog is big (pointing outward, real dog)
Mention: Draw attention to the word itself.
Ex. “Dog” is “God” spelled backwards. (means the actual word)
Grammatical Ambiguity
A confusing grammatical construction rather than the meaning of words.
Other Useful Distinctions
Analytic Statements
True by definition. Ex. All triangles have three sides.
Synthetic Statements

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Statements whose truth or falsity does not depend merely on the meaning of the
terms. Ex. Socrates drank the hemlock in 399 BC (unable to tell if it is true on
false based off the words)
Contradictory Statements
False by definition. Ex All triangles have four sides. *Different from inconsistent
sets because there is only one statement.
Necessary and Sufficient Conditions
Antecedent: The conditional that has to be met for a claim to be true or for
something to occur.
Consequent: The outcome state.
Ex. What temperature must it be (antecedent) for snow to fall (consequent)?
Necessary Condition
No X, No Y. (Without X, Y cannot occur.)
Ex. You must be a male to be a citizen in ancient Athens. If you are not a male,
you are not a citizen.
How to show a necessary condition statement is false: Look for an instance of Y
that is not also an instance of X.
Sufficient Condition
X is a guarantee of Y.
When X is present, Y must occur.
Ex. Being a cat is a sufficient condition of being a mammal. If the animal is a cat,
it is guaranteed that it is a mammal.
How to show a sufficient condition statement is false: Instances when X did not
guarantee Y.
Conditions that are both Necessary and Sufficient
Having a grade of 50% or higher is both necessary and sufficient for passing
Individually Necessary and Jointly Sufficient Conditions
Necessary conditions, taken singly, are not sufficient conditions because they do
not guarantee the consequent.
Taken together, they might guarantee the consequent.
Ex. For Athenian citizenship, you must follow 6 characteristics: male, over 18,
completed military service, not a slave, not a foreign resident, do not owe debt to
the city.
You need to fit all the criteria to become a citizen. Ex. being male is necessary,
but not sufficient.
 In clarifying the meaning: Being male is a condition of being a citizen of
Athens. True if you meant necessary condition. False if you mean sufficient
The Republic
Thrasymachus’ Definition of Justice
He enters the argument seeking to dominate it.
“Justice is the advantage of the stronger.”
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