LOGIC Immediate Inference Three kinds of immediate inferences Conversion Obversion Contraposition Conversion is an inference that proceeds by interchanging the subject and predicate terms of the proposition No men are angels converts to No angels are men and these proposition ID: 1010136
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1. LOGICImmediate Inference
2. LOGICImmediate Inference: ( Three kinds of immediate inferences)ConversionObversionContraposition
3. Conversion is an inference that proceeds by interchanging the subject and predicate terms of the proposition. “No men are angels” converts to “No angels are men,” and these propositions may be validly inferred from one another. Conversion is perfectly valid for all E propositions and all I propositions.
4. In this immediate inference the premise is called converse and the conclusion is called convertend.Thus “ No idealists are politicians” is the converse of “ No politicians are idealists,”which is its convertend. The conversion of an O proposition is not, general valid.
5. The A Proposition presents a special problem here. For example, from ”All dogs are animals” We certainly may not infer that “All animals are dogs.” From “All S is P” to “Some P is S” this pattern of inference , called conversion by limitation.
6. ObversionOVERVIEWObvertend Obverse A: All S is P E: No S is non-PE: No S is Obversion A: All S is non -P I: Some S is P O: Some S is not non- PO Some S is not P I: Some S is non -PTo obvert a proposition, we change its quality and replace the predicate term with its complement.
7. CONTRAPOSITIONA third type of inference, contraposition can be reduced to the first two, conversion and obversion. To firm a contrapositive of a proposition,We replace its subject term with the complement of its predicate term, and we replace its predicate term with the complement of its subject term. Neither the quality nor the quantity of the original proposition is changed
8. The contrapositive of A proposition is an A proposition, the contrapositive of an O proposition is an O proposition.