CONTRAPOSITION Contraposition of A

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Course: UG Semester: 2 Paper code: PHILGE202 Paper name: Formal Logic/Symbolic Logic Topic: Contraposition Faculty name: Dr. Kumkum Rani Department: Philosophy Email Id: [email protected] CONTRAPOSITION Contraposition is a kind of Immediate inference in which from a given proposition we infer another proposition having for its subject the contradictory of the given predicate. The conclusion in Contraposition is called the Contrapositive; but there is no corresponding name for the given proposition. The Rule of Contraposition are the following: The subject of the conclusion is the contradictory of the predicate of the given proposition. The predicate of the conclusion is the subject of the given proposition. The quality is changed i.e , if the given proposition be affirmative the conclusion is negative and vice versa. No term can be distributed in the conclusion, if it be not distributed in the given proposition. Contraposition, is a compound form of Immediate Inference, which involves both Obversion and Conversion. The simple rule of Contraposition is First Obvert, then Convert. Contraposition of A An A proposition when obverted given E, and E when converted gives E. Therefore, the Contrapositive of A is E. A- All S is P. Obverse E- No S is not P. Converse of E is E-No not P is S. Contraposition of E. E obverted gives A, and A converted gives I. Therefore the contrapositive of E is I. Thus E- No S is P. Obverse A- All S is P Converse of A is I-Some P is S. In this case the given proposition is universal but the contrapositive is particular, because if we attempt to draw a universal proposition in the conclusion ,we shall have to distribute the subject not predicate, which is not distributed in the premise 2 that is A. Contraposition of I. All I proposition, when obverted gives O, but an O proposition cannot be converted . Hence an I proposition cannot be contraposed. Contraposition of O An O proposition when obverted gives an I proposition which when converted , gives an I proposition again. Therefore, the contrapositive of O is I. Thus, O – Some S is not P Obverse I- Some S is P Converse of I is I – Some P is S To sum up: By controposition A gives E , E gives I , O gives I but I cannot be contraposed. .

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