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Square of Opposition-1

# Square of Opposition-1 - Todays Topics(12/2 I Immediate...

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3/4/11 Today’s Topics (12/2) I. Immediate Inferences a. Taking the Converse b. Conversion c. The Complement of a Class d. Taking the Obverse e. Obversion f. Taking the Contrapositive g. Contraposition I. The Square of Opposition a. Contradictories Contraries

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3/4/11 I. Immediate Inferences I mmediate I nferences : Arguments with exactly one premise. They may or may not be valid. Example: 1. If James drives drunk, he breaks the law. 2. If James does not break the law, he does not drive drunk.
3/4/11 I.a. Taking the Converse To take the converse of a categorical proposition, switch the subject and predicate terms. A Categorical Proposition The Converse Categorical Proposition All bananas are fruit. All fruit are bananas. No banana is a vegetable. No vegetable is a banana. Some people are musicians. Some musicians are people. Some teachers are not hipsters Some hipsters are not teachers.

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I.b. Conversion Conversion is a form of immediate inference in which: a. The premise is a categorical proposition; and A-Propositions: 1. All bananas are fruit. 2. All fruit are bananas. (I NVALI D) E-Propositions: 1.No banana is a vegetable. 2. No vegetable is a banana. (VALI D) I -Propositions: 1.Some politicians are corrupt people. 2. Some corrupt people are politicians. O-Propositions: 1.Some dogs are not Chihuahuas. 2. Some Chihuahuas are not dogs. Conversion is a valid form inference for E- and I-propositions. It is not a valid form of inference for A- and O-propositions
3/4/11 I. c. The Complement of a Class The Complement of a Class : The class of everything in the universe not included in the class. Examples : Ø The complement of the class of birds is the class of everything that is not a bird. Ø The complement of the class of everything that is not a triangle is the class of triangles.

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I. d. Taking the Obverse To take the obverse of a categorical proposition, a. replace the predicate term with its complement; and b. switch the quality of the proposition (from Categorical Proposition The Obverse of the Categorical Proposition All dogs are canines. No dog is a thing that is not a canine No penguin is a snake. All penguins are things that are not snakes.
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Square of Opposition-1 - Todays Topics(12/2 I Immediate...

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