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# Critical Thinking Chapter 3 Notes.docx

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Ryerson University

Social Sciences and Humanities

SSH 105

Joseph Zboralski

Fall

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Critical Thinking Chapter 3 Notes Conditional statement is a statement of the form:
If P... then Q
Conditionals are compound statements composed of two parts:
Antecedent – what follows the word “if”
Consequent – what follows the word “then”
Necessary Conditions:
A is necessary for B. Without A, B would not be true
Sufficient Conditions:
A is a sufficient condition for B. If A is true, then B is true
Ex. If John is a bachelor, then John is unmarried.
"then John is unmarried" - is a Consequent, necessary condition
"John is a bachelor" - is a Antecedent, sufficient condition
Therefore:
Conditional Statement
1. Antecedent expresses a sufficient condition
2. Consequent expresses a necessary condition
Valid Conditional Arguments:
1. Affirming the Antecedent (Modus Tollens)
If P, then Q
P
Therefore, Q
Must be Valid. (true premises = true conclusion)
Ex. (1) If a shape is a square, then it has four sides
(2) The shape is a square
Therefore,
(3) It has four sides
2. Denying the Consequent
If P, then Q
Not Q
Therefore, not P
Must be Valid (true premises = true conclusion)
Ex. (1) If a shape is a square, then it has four sides
(2) The shape is not have four sides ___________________________________
Therefore,
(3) It is not a square
3. Hypothetical Syllogism (Chain Argument)
If P, then Q
If Q, then R
Therefore, if P, then R
Must be Valid (true premises = true conclusion)
Syllogism- an argument made up of three statements (two premises, one conclusion)
Not Valid Conditional A

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